Comparison devices metrology. State metrological service

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INTRODUCTION

The entire history of mankind has been and is accompanied by the use of measurements: without them, not a single scientific discovery or invention is possible. More M.V. Lomonosov wrote: "To measure through geometry, to hang through mechanics, to look out through optics." Measurements are the source of our scientific knowledge. “In physics, there is only that which can be measured” (Max Planck).

The production of industrial products is accompanied a large number all kinds of measurements. By means of measurements, the conformity of manufactured parts and products as a whole to the requirements is determined. design documentation. It has been calculated that the share of expenditures on measuring equipment is at least 15% of the expenditures on equipment in mechanical engineering and over 25% in radio electronics, aircraft building, chemical and some other industries.

The improvement in product quality is largely due to how well the measuring service of the enterprise is organized. It is impossible to manage this or that process without monitoring its indicators.

The improvement of measurement techniques, which is manifested in an increase in the accuracy of measurements and in the creation of new methods and instruments, contributes to new achievements in science.

So, for example, an increase in weighing accuracy by one sign led to the discovery in 1892-1984. new argon gas, which, due to the inaccuracy of measurements, could not be detected before. The introduction of the microscope into experimental practice created exceptional opportunities for the study of microorganisms and led to the creation of microbiology. Often the need to study certain phenomena necessitates the creation of new, more advanced equipment. New discoveries in science, in turn, lead to the improvement of measurement techniques, as well as to the creation of new instruments.

First attempts at quantitative research electrical phenomena in nature required the creation of special measuring instruments for this purpose. Back in 1744, M.I. Lomonosov expressed the remarkable idea that "electricity can be weighed." To this end, he, together with G.V. Richman created the world's first electrical measuring device - "pointer electrical force", which had a pointer and a scale.

Later, as the theory of electricity developed, new laws were discovered, on the basis of which new methods of measurement and instruments were developed, and the practice of measurement was improved.

Before the opening of radio A.S. Popov, the measurement developed only in the region direct current and low frequency. But already in 1905 A.S. Popov proposed a differential bridge for measuring small capacitances, which was used to take into account the influence of rigging on the operation of ship antennas. In the same year, at a meeting of the Physics Department of the Russian Physico-Chemical Society, he made a report "On the Determination of the Wavelength and the Period of Oscillations", in which he reported on the resonant wavemeter he had invented.

With the advent of measuring instruments and the development of measurement methods, arose new area sciences - metrology - as a science of precise measurements.

A great contribution to the development of domestic metrology was made by D.I. Mendeleev, who in 1893 headed the Main Chamber of Measures and Weights, whose tasks included not only storing standards and ensuring verification of measuring instruments against them, but also conducting scientific research in the field of metrology. Local verification chambers began to be created.

Academician M.V. Shuleikin, who in 1013 organized the first factory laboratory for the production of radio measuring instruments. A great contribution to the development of radio measurements was made by Academician L.I. Mandelstam, who created a prototype of a modern electronic oscilloscope at the beginning of the 20th century.

The theoretical basis of measurements is metrology - the science of measurements, methods and means of ensuring their unity and ways to achieve the required accuracy.

The concept of "measurement" is found in various sciences(mathematics, physics, chemistry, psychology, economics, etc.), but in each of them it can be interpreted differently. In this study guide only problems related to measurements of physical quantities in the field of radio electronics are considered.

These include:

measurement of the parameters of parts or elements that make up the measured object;

measurement of the modes of individual parts, assemblies and the entire measured object;

Graduation or verification of graduation of scales of various instruments;

Removal of characteristics that determine the properties of instruments and devices;

Determination of signal distortions as they pass through various devices;

· measurement of parameters of modulated signals;

measurement of the intensity of electromagnetic fields, both useful and interfering;

Finding faults in radio equipment and determining their nature.

In addition, this includes measurement errors, ways to take them into account and reduce them, and evaluate measurement results.

1. BASIC TERMS AND DEFINITIONS IN THE FIELD OF METROLOGY

In any science, an arbitrary interpretation of the terms used is unacceptable. Terminology in the field of metrology is regulated by GOST 16263-70 “Fuels and Lubricants. Metrology. Terms and Definitions". For each concept, one standardized term is established, which is given an appropriate definition.

Metrology is the science of measurements, methods and means of their unity and ways to achieve the required accuracy. In this regard, we can formulate the main tasks of metrology: theoretical questions ensuring the uniformity of measurements and achieving the required accuracy; establishing binding rules, requirements and organizational measures aimed at achieving these goals.

There are theoretical and legal metrology.

Theoretical metrology includes the development and improvement theoretical foundations measurements and measuring equipment, scientific foundations for ensuring the uniformity of measurements in the country. It includes the following main issues:

development of the general theory of measurements and the theory of errors, including the creation of new measurement methods and the development of ways to eliminate or reduce errors;

creation and improvement of systems of units of physical quantities;

Creation and improvement of the system of standards;

· Creation and improvement of the scientific bases for transferring the sizes of units of physical quantities from standards to working measuring instruments.

Legal metrology is a section of metrology that includes complexes of interrelated and interdependent general rules, requirements and norms, as well as other issues requiring regulation and control by the state, aimed at ensuring the uniformity of measurements and the uniformity of measuring instruments. Its main tasks:

Creation and improvement of the system state standards, which establish the rules, requirements and norms that determine the organization and methodology for carrying out work to ensure the unity and accuracy of measurements;

organization and functioning of the relevant public service.

The purpose of the measurement is to determine the size of the quantity, and the result of the measurement must be expressed as a number.

A possible working description of the term "measurement", consistent with our intuition, is: "Measurement is the acquisition of information." One of the most essential aspects of measurement is the collection of information. This means that the measurement result should describe the state or phenomenon in the world around us that we are measuring. Although obtaining information is obvious, it is only necessary, but not sufficient, to determine the measurement: when someone reads a textbook, he accumulates information, but does not take measurements. The second aspect of measurement is that it must be selective. It can only provide us with information about what we want to measure (about the quantity being measured) but does not tell us anything about any of the many other states or phenomena around us. The third aspect is that the measurement must be objective. The outcome of the measurement should not depend on the observer. Any observer must extract the same information from the measurements and come to the same conclusions.

Measurement is a set of operations for the use of a technical means that stores a unit of a physical quantity, which consists in comparing (explicitly or implicitly) the measured quantity with its unit in order to obtain the value of this quantity (or information about it) in the most convenient form for use.

A physical quantity is a characteristic of one of the properties of a physical object, which is qualitatively common for many physical objects ( physical systems, their states and the processes occurring in them), but quantitatively individual for each object.

The measurement process consists in comparing the measured quantity with some of its value, taken as a unit.

The measurement result is a number showing the ratio of the value of the measured quantity to the unit of measurement.

A unit of measurement is a physical quantity with numerical value"1", taken as the basis for comparison with quantities of the same kind. Units of measurement are divided into basic and derived. To be able to compare the results of measurements performed in different time and in different places, the system of units is established by law (GOST 8.417-81 GSI). We have accepted International system units (SI), built on seven basic units: meter, kilogram, second, ampere, candela, kelvin, mole. Based on these values, derived SI units are formed (table 1.1).

Table 1.1 - SI derived units



			m -1хkgхs-2
			m -2хkgхs-2
			m -2хkgхs-3

			m 2xkgxc3xA-1
			m -2хkgхs-3хА-2
			m 2хkgхs-2хА-2
			m -2xkg-1xc3xA2
			m 2хkgхs-2хА-1

			m2hkghs-2hA-2

			m-2hkdhsr
becquerel

In communication technology, the off-system logarithmic unit decibel (DB) is widely used, with the help of which the relative values of gain, attenuation, non-linear distortion, and uneven characteristics are determined.

1 dB is equal to 10 lg of the ratio of two energy quantities of the same name (power, energy) at P1/P2 = 101/10 = 1.259. For "power" quantities (voltage, current, field strength) 1 dB is equal to 20 lg of their ratio, if U1 / U2 \u003d 101/20 \u003d 1.22.

To express the quantitative difference between the quantities of the same name, the concept of the size of a physical quantity is used - the quantitative content in given object properties corresponding to the concept of "physical quantity". The size of a quantity exists objectively, regardless of whether we know it or not, whether we can measure it or not.

The dimension of a physical quantity is an expression in the form of a power monomial, composed of the products of the symbols of the basic physical quantities in various degrees and reflecting the relationship of this physical quantity with the physical quantities accepted in this system of quantities as the main ones, and with a proportionality coefficient equal to one.

Not every physical quantity can be measured, since not every physical quantity can be compared with its values. A measurable quantity can only be such, from the definition of which the concepts of "more" and "less" and the possibility of comparing values follow. Obviously, the measured value can take the value "0".

Most physical quantities satisfy these requirements. For example, mass, length, inductance, resistance, etc. But such a quantity as hardness requires a special definition in order to be able to measure. Indeed, if we judge hardness by whether diamond, corundum, topaz, quartz, feldspar, etc., successively leave scratches on the test object, as is customary in mineralogy, then such a definition of hardness does not contain necessary elements to carry out the measurement. But Brinell's definition, according to which hardness is measured by the diameter of a recess in the test object, obtained under known conditions, already satisfies the requirements of measurability.

The value of zero for a number of cases is conditional. For example, when measuring the degree of heating of bodies, we are forced to agree on the "reference point" ( zero value) and, in essence, measure not body temperature, but only a conditional temperature interval, a temperature difference.

The above definition of the measurement process assumes that the unit of measurement is an obligatory link in this process.

All of the above assumes the legitimacy of the accepted terminology and the associated existence of such concepts as the unity of measurements and the uniformity of measuring instruments.

Unity of measurements - the state of measurements, in which their results are expressed in legal units and measurement errors are known with a given probability.

Uniformity of measuring instruments - the state of measuring instruments, characterized by the fact that they are graduated in legal units and their metrological properties comply with the standards.

To organize ensuring the uniformity of measurements and uniformity of measuring instruments, a metrological service has been created in the country.

Metrological service - a network of state and departmental bodies and their activities aimed at ensuring the uniformity of measurements and the uniformity of measuring instruments in the country. These bodies supervise the state of measuring instruments and ensure the transfer of the size of units of physical quantities from standards to working measuring instruments.

Any measurement must be preliminarily considered, a plan for carrying out measurements must be drawn up. In this regard, in the theory of measurements, such a concept as a measurement technique is introduced.

Measurement technique - a detailed schedule of the measurement process with a selected scheme and a set of instruments, including rules, sequence of operations, number of measurements, etc. With regard to the same measurement scheme and a given set of equipment, different methods are possible, and vice versa, for measurements using one method, you can use various schemes measurements and equipment.

In the process of measuring or setting the parameters of signal sources, the operator takes readings or readings.

The countdown is the number indicated by the instrument indicator. In pointer instruments, the reading is the number written at the division of the scale on which the arrow was set; in digital - the number observed on the front panel in the form of luminous numbers; sometimes the reference is the number written at the division of the limb, located against the hairline.

Indication - a physical quantity corresponding to the reading. The reading is obtained by multiplying the reading by the conversion factor.

For example, if the reading on the voltmeter scale is 20 V, the “Multiplier” switch is set against 0.1, then the reading of the device will be 2 V.

2. CLASSIFICATION OF MEASUREMENTS

The information obtained in the process of measurements is called measuring.

According to the method of obtaining measurement information, measurements are divided into direct, indirect, cumulative and joint.

Direct measurement is a measurement in which the desired value of a physical quantity is found directly from experimental data (for example, measuring the current strength with an ammeter). Mathematically direct measurements can be written by the elementary formula

where Q is the desired (true) value of the physical quantity;

X - the value of a physical quantity found by measuring it and called the measurement result.

Indirect measurement - a measurement in which the desired value of a quantity is found on the basis of a known relationship between this quantity and the quantities subjected to direct measurements. Indirect measurements are expressed by the following formula:

Q = F(X1 X2,... Xm) (2.2)

where X1 X2, ... Xm are the results of direct measurements of quantities related to the known functional dependence F with the desired value of the measured quantity Q (for example, when measuring resistance using the ammeter-voltmeter method, the results of direct measurements are voltage and current strength, and the result of indirect measurements will be the resistance found according to Ohm's law).

Cumulative measurements - simultaneous measurements of several quantities of the same name, in which the desired values \u200b\u200bof the quantities are determined by solving a system of equations obtained from direct measurements various combinations these quantities (for example, determining the mass of individual weights of a set from the known mass of one of them).

Joint measurements - simultaneous measurements of two or more dissimilar quantities to determine the relationship between them (for example, taking the current-voltage characteristic of a diode).

Aggregate measurements are based on known equations that reflect an arbitrary combination of quantities, and joint measurements are based on equations that reflect the existence of a relationship between the measured quantities.

If the measured value remains constant during the measurement process, the measurements are called static, if it changes - dynamic. Dynamic measurements can be continuous (if the technical means allow you to continuously monitor the values of the measured quantity) and discrete (if the values of the measured quantity are recorded only in individual moments time).

According to the method of expressing the results of measurement, they are divided into absolute and relative.

Absolute measurement - a measurement based on direct measurements of one or more basic quantities and (or) the use of the values of physical constants. The measurement result is expressed directly in units of a physical quantity.

Relative measurement - measurement of the ratio of a value to a value of the same name, which plays the role of a unit, or a change in a value with respect to a value of the same name, taken as the initial one (for example, determining the gain as the ratio of the voltages at the input and output of the device). The value obtained as a result of relative measurements can be either dimensionless or expressed in relative logarithmic units (bel, octave, decade) and other relative units.

Depending on the conditions that determine the accuracy of the result, measurements are divided into three classes:

one). measurements of the highest possible accuracy achievable with the current state of the art:

reference (the maximum possible accuracy of reproduction of the size of a physical quantity is achieved);

measurement of physical constants;

· astronomical;

2). control and verification measurements - measurements, the error of which should not exceed a certain set value. For such measurements, exemplary measuring instruments are used, and the measurements themselves are carried out in special laboratories;

3). technical (working) measurements - measurements in which the error of the measurement result is determined by the characteristics of the measuring instrument. Measuring instruments used for this purpose are called working.

In turn, technical measurements are divided into operational ones, used to control the operating equipment and performed by standard factory-made measuring instruments; production, carried out in workshops and serving to measure the parameters of parts from which components and blocks of equipment are assembled; measurements of the modes established in blocks and knots; characterization of these nodes and the entire device as a whole; measurements during installation, adjustment and adjustment; acceptance test measurements finished products, installations and objects and performed mainly by standard measuring instruments; laboratory, produced at scientific research and development of new systems, devices and devices.

3. CLASSIFICATION OF MEASURING INSTRUMENTS

Measuring instrument - technical means(or their complex), intended for measurements, having normalized metrological characteristics, reproducing and (or) storing a unit of physical quantity, the size of which is assumed to be unchanged (within the established error) for a known time interval.

According to their technical and metrological purpose, according to GOST 16263-70 GSI, measuring instruments are divided as follows:

measures - measuring instruments designed to reproduce a physical quantity given size;

· measuring instruments- measuring instruments designed to obtain measurement information in a form accessible to direct perception by an observer;

· measuring transducers- measuring instruments designed to generate a signal of measuring information in a form convenient for transmission, further transformations, processing and (or) storage, but not amenable to direct perception by the observer.

In addition, a combination of various measuring instruments can form:

measuring installations - a set of measuring instruments located in one place and functionally combined with each other, designed to generate a signal of measuring information in a form convenient for direct perception by the observer;

· measuring systems- a set of measuring instruments designed to generate measurement information signals in a form convenient for automatic processing, transfer and (or) use in automatic systems management.

By metrological purpose, measuring instruments are divided as follows:

standards - measuring instruments (or a set of measuring instruments) that ensure the definition, reproduction and storage of a unit of physical quantity in order to transfer the size of a unit of physical quantity to exemplary, and from them to working measuring instruments and approved as a standard in in due course;

exemplary measuring instruments - measures, measuring instruments or measuring transducers that have high precision and intended for verification and calibration of other measuring instruments, duly approved as exemplary;

· workers - measuring instruments used for measurements not related to the transfer of the size of units.

4. CLASSIFICATION OF MEASUREMENT METHODS

Measurements are based on certain principles.

Measuring principle - totality physical phenomena on which the measurements are based.

Method of measurement - a combination of the use of principles and means of measurement.

There are two main measurement methods: the direct evaluation method and the comparison method.

Direct evaluation method - a measurement method in which the value of a quantity is determined directly from the reading device of a direct-acting measuring device. This method is sometimes referred to as the direct conversion method.

Comparison method - a measurement method in which the measured value is compared with the value reproduced by the measure.

The comparison method can be implemented in following modifications:

· zero method (compensation) - a method in which the resulting effect of the impact of quantities on the comparator is brought to zero;

differential method - a method in which the difference between the measured and the known value, reproducible by the measure, is formed and measured;

Coincidence method - a method in which the difference between the measured and known quantities is measured using the coincidence of scale marks or periodic signals;

· opposition method - a method in which the measured and known quantities simultaneously act on the comparison device, with the help of which the ratio between these quantities is established.

Depending on the measurement method and the properties of the measuring instruments used, all measurements can be performed either with single or multiple observations.

Here it is also appropriate to define the observation and the measurement algorithm.

Observation is a single experimental operation, the result of which - the result of observation - is always random.

The measurement algorithm is a prescription on the procedure for performing operations that ensure the measurement of the desired value of a physical quantity.

5. CLASSIFICATION OF ERRORS

Any measurement is always performed with some error, which is caused by the imperfection of the methods and means of measurement, the inconsistency of the observation conditions, as well as the insufficient experience of the experimenter or the peculiarities of his senses.

Measurement error - deviation of the measurement result X from the true value of the measured quantity Q: ? = X - Q.

Since the true value of the physical quantity Q is unknown in practice,

in the calculations, the so-called real value of Xg is used, which is found experimentally and is so close to the true value that it can be used instead.

Depending on the nature of the manifestation of errors, they have the following components:

Random error - an error that varies randomly for repeated measurements of the same quantity (for example, the error resulting from rounding);

systematic error - an error that remains constant or regularly changes during repeated measurements of the same value (for example, an error that appears due to a discrepancy between the actual and nominal values of the measure);

Gross error - an error that significantly exceeds what is expected under given conditions.

All these errors appear at the same time.

Depending on the nature of the influence on the measurement result, the following errors are distinguished:

· additive - errors, the values of which do not depend on the value of the measured value;

· multiplicative - errors, the values of which change with a change in the measured value.

These errors can be both systematic and random at the same time.

Depending on the source of occurrence, errors are classified as follows:

· methodical - errors arising from the imperfection of measurement methods and processing of their results. As a rule, these are systematic errors;

instrumental (hardware) - errors, which are determined by the errors of the measuring instruments used;

external - errors due to the deviation of one or more influencing quantities from normal values (for example, temperature, humidity, magnetic and electric fields, etc.). These errors are systematic;

Subjective (personal) - errors due to the individual characteristics of the experimenter. They can be either systematic or random.

6. ERRORS OF MEASURING INSTRUMENTS

The error of measuring instruments is the difference between the readings of the measuring device and actual value measured value. It includes in general case systematic and random components.

GOST 8.009-84 GSI "Normalized metrological characteristics of measuring instruments" provides for the following indicators of accuracy of measuring instruments:

· limit, mathematical expectation and root-mean-square deviation of the omitted systematic component of the error;

limit of permissible standard deviation and autocorrelation function or the spectral density of the random component of the error.

The errors of measuring instruments can be presented in the following forms:

absolute error - the difference between the measured X and the true Q value of the measured quantity:

In this case, a correction is introduced into the measurement result - the value of the quantity of the same name as the measured one, added to the value of the quantity obtained during the measurement in order to eliminate the systematic error:

Relative error - the ratio of the absolute error to true value measured quantity

Often in measurement technology they use such a concept as measurement accuracy - a characteristic of the quality of a measurement, reflecting the closeness of their results to the true value of the measured value. Quantitatively, this is the reciprocal of the modulus of the relative measurement error

reduced error - the ratio of the absolute error to some normalizing value XN

AT this case XN is a conditionally accepted value, which can take various meanings depending on the type of scale. In the case when the scale of the device is uniform and "0" is at the beginning of the scale (the most common case in measurement technology), the measurement limit is taken as XN.

If "0" is in the middle of a uniform scale, then the sum of the modules of the measurement limits is used as Xn, and if the scale does not have zero (for example, a medical thermometer), then the normalizing value is taken equal to the difference between the modules of the measurement limits. The situation is more complicated with uneven scales, i.e. such scales, in which the same interval corresponds different meanings measured value. In this case, either the difference between the modules of the limits of the uniform sections of the scale, or the length of the scale in millimeters is taken as the normalizing value. Last case introduces certain difficulties, since in this case the value of the measured physical quantity must be reduced to the dimension of length.

The error values are set for normal conditions, i.e. such conditions for the use of measuring instruments, under which the quantities influencing the measurement process have the values specified in the relevant standards for measuring instruments of this type. The following conditions are generally accepted as normal: temperature environment(20±5) °С, relative air humidity (65±15)%, Atmosphere pressure(100000 ± 4000) Pa. The error value is also influenced by the position of the instruments, electromagnetic fields, stability external conditions etc.

The error inherent in measuring instruments located in normal conditions, is called the basic error.

The deviation of external conditions from normal leads to a change in errors, and then there is an error, called additional.

The basic error of the measuring instrument is normalized by setting the limits of the permissible main and additional errors, i.e. the greatest error of the measuring instrument (without taking into account the sign), at which it can be recognized as fit and allowed for use. Methods for normalizing the limits of permissible measurement errors are regulated by GOST 8.009-84 GSI and GOST 8.401-80 GSI.

Depending on the nature of the change in the error within the range, as well as on the conditions for using a measuring instrument of this type, the errors of measuring instruments are normalized as follows:

a) in the form of an absolute error:

One value

where a=const, for additive error;

For multiplicative error;

Table?n for different levels(or ranges);

b) in the form of a relative error:

One value for additive error;

The value for the multiplicative error;

where Hk - final value range. The values q, c, d are selected from the series

(1; 1.5; 2; 2.5; 4; 5; 6)x10n (6.5)

where n=+1,0,-1,-2,...;

If the measurement range includes zero, then in this case the relative error tends to infinity, and the basic error of the measuring instrument is normalized by the reduced error

Depending on the limits of permissible error, all measuring instruments are divided into accuracy classes (table 6.1).

The accuracy class of a measuring instrument is a generalized characteristic of a measuring instrument, determined by the limits of permissible basic and additional errors, as well as other properties of the measuring instrument that affect the accuracy, the values of which are set in the standards for certain types measuring instruments.

The value of the accuracy class is also selected from the series (6.5).

The method of designating the accuracy class is determined by the form of expression of the basic error.

Table 6.1 - Examples of designation of accuracy class

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7 SYSTEMATIC MEASUREMENT ERRORS

7.1 Classification of systematic errors

Errors that do not change over time or are functions of certain parameters that do not change over time are called systematic errors. Them hallmark is that they can be predicted and, therefore, almost completely eliminated by the introduction of appropriate corrections.

Systematic additive errors, for example, can arise from an extraneous load on the scale pan, from inaccurate setting of the device to "0" before measurement, from thermo-EMF. in DC circuits. To eliminate them, the devices have a zero corrector. Systematic multiplicative errors are, for example, a change in the gain of an amplifier, a change in the stiffness of the membrane of a pressure gauge sensor or a spring of an instrument, or a reference voltage on a digital voltmeter.

Depending on the causes of occurrence, systematic errors are divided into instrumental, external, personal, as well as method errors.

Instrumental errors are caused by the aging processes of certain parts of the equipment (discharge of power supplies; aging of resistors, capacitors; deformation mechanical parts, shrinkage of paper tape in recorders, etc.). Their peculiarity lies in the fact that they can be adjusted by introducing an appropriate correction only at a given point in time, and then increase again unpredictably. As a result, a continuous repetition of the correction is required, the more frequent, the smaller their residual value should be.

According to the nature of manifestation, systematic errors are divided into constant and variable.

Constant systematic errors do not change magnitude and sign during the measurement process, and therefore it is very difficult to detect them in the measurement results. Outwardly, they do not manifest themselves in any way and can for a long time go unnoticed. The only way to avoid them is the verification of the device by re-certification according to exemplary measures or signals.

Variable systematic errors either monotonously change their value (progressive errors), or change periodically (periodic: errors). All other types of systematic errors are usually called errors that change according to a complex law.

The presence of systematic errors distorts the measurement results. Their absence determines the correctness of measurements (or the correctness of measuring instruments).

The correctness of measurements (measuring instruments) is the quality of measurements (measuring instruments), reflecting the closeness of systematic errors to zero.

The task of ensuring the correctness of measurements is the detection of systematic errors with their subsequent full or partial compensation.

7.2 Detection of systematic errors

The main difficulty is the detection of systematic errors and the determination of their magnitude and sign. It is necessary to carry out special experimental studies. Often they use a graph of the sequence of values of random deviations of observational results containing systematic errors from arithmetic means. The essence of this experiment is as follows. Find n measurement results X1, X2, ... Xn, their average value

and deviations of the measurement results from their average value Vi=Xi-X. Based on these data, a graph of the Vi sequence is constructed depending on the number of observations. The type of graph depends on the nature of the systematic error.

If Vi changes sharply with changes in the observation conditions (Figure 7.1), then these results contain a constant systematic error depending on the observation conditions. From the analysis of the graph, it follows that the first four points were obtained under the same conditions (with one device), the remaining six in others. Therefore, one of the instruments introduces a constant systematic error.

If Vi monotonically decreases (Figure 7.2), then this means that there is a progressive decreasing systematic error in the measurement results. This method of detection is suitable when the random components of the error are much smaller than the systematic ones. In addition, graphs only allow you to detect the systematic error, without giving information about its value. Its quantitative assessment is based on the results of special studies, the methodology for which depends on the nature of the experiment and the sources of errors. For example, if the instrument was calibrated according to an exemplary measure, then the measurement of the difference between the average value of the measured quantity and the value of the measure is carried out with an accuracy determined by the measure's certification error and random measurement errors.

This will be the constant component of the systematic measurement error.

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7.3 Methods for reducing systematic errors and introducing corrections

7.3.1 Before starting measurements, it is necessary

Carefully set zeros and perform calibration (for example, oscilloscope sweep calibration using a quartz duration calibrator);

Verify working measuring instruments with the determination of the absolute value and the sign of the systematic error (corrections);

warm up the devices for the time specified in the operating instructions;

When assembling circuits, use short connecting wires, especially when measuring on high frequencies;

Proper placement of gauges. At the same time, attention should be paid to the installation of devices in the working position (vertical or horizontal, in accordance with the signs printed on the body of the devices) and to the mutual position of the devices, excluding communication between them through an electromagnetic field; remove them from heated objects, strong sources of electric and magnetic fields;

Apply screening and temperature control of devices.

7.3.2 In the process of measurements, systematic errors or their individual components can be eliminated in the following ways

substitution method. In this case, the measured value is replaced by an exemplary Measure, which is in the same conditions as the measured value;

A way to compensate for the error in sign. In this case, the measurement or reading of the measured quantity is performed twice, so that an error not known in magnitude, but known by nature, enters the result with opposite signs. The half-sum of readings is free from systematic errors. As an example, we can cite a method for eliminating the frequency meter error that occurs due to the presence of a backlash in the tuning mechanism, when tuning is carried out once from the side of smaller divisions of the reference scale, and the second - from the side of large divisions;

a method of symmetrical observations. Measurements are carried out sequentially at the same intervals of change of the argument. The final result is the average value of any pair of symmetrical observations relative to the middle of the measurement interval. This is how often temperature, time, pressure, etc. are measured;

the method of randomization, i.e. conversion of systematic errors into random ones. Let there be n devices of the same type with systematic errors of the same origin. From device to device, the error varies randomly. Therefore, it is possible to make measurements with different instruments and average the measurement results.

7.3.3 After measurements: when processing the results, systematic errors with known values and signs can be excluded

To do this, corrections q or correction factors are introduced into the uncorrected observation results. The results of measurements after making corrections are called corrected.

The correction is the value of the quantity of the same name as the measured one, added to the value of the quantity obtained during the measurement to eliminate the systematic error:

Correction factor - the number by which the measurement result is multiplied in order to eliminate the systematic error:

At the same time, it must be remembered that the correction eliminates the additive systematic error, and the correction factor excludes the multiplicative one. The correction and correction factor are determined during verification or by special studies.

7.4 Summation of non-excluded systematic errors

Systematic errors that remain in the measurement results after detection, evaluation, and elimination are called non-excluded systematic errors.

When determining the boundary of the resulting non-excluded systematic error, its individual components are considered as random variables. If it is known that the distribution of the components of the non-excluded systematic error is normal, then

where is the value of the non-excluded component of the systematic error;

m is the number of non-excluded systematic errors.

If there is no data on the type of distribution, then

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At Rd=0.95 coefficient k=1,l. At Pd=0.99 k depends on the number of non-excluded systematic errors m. If m>4, then k=1.4.

For m?4 proceed as follows. Find an attitude

where?" ci is the component of the systematic error, which differs most in its value from the rest;

?”Ci is the component of the systematic error, which in its value is closest to?”Ci. Then, according to the plot of k versus 1 shown in Figure 7.3, the value of k is found. indirect measurements non-excluded systematic errors are private non-excluded systematic errors of indirect measurement:

8. DISTRIBUTIONS OF RANDOM VARIABLES AND THEIR NUMERICAL CHARACTERISTICS

Due to the fact that the measurement result X contains a random error, it is itself a random variable, since X=Q+?.

The main characteristic of any random variable is a probability distribution function that establishes a relationship between possible values random variable and the probabilities of their occurrence in multiple measurements.

There are two forms of representation of a random variable: integral and differential.

The integral distribution function of the observation results is a function. F(X) - the probability that the observation result will be less than some current value x: F(X)=P(X

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The main property of this function is the following: the probability that a random variable takes values in the interval (x1 x2) is equal to the difference between the values of the function at the ends of the interval: P(xi

If x2-x1=?x, then the same increments?x correspond to different values of the probability increment?F(x). Then the probability distribution density of a random variable, or probability density, will have the following form:

This is the differential form of the representation of F(x). In integral form

The probability of a random variable falling into the interval (x1 x2) will be equal to the integral of the probability distribution density:

Since? = X-Q, then the transition from the laws of distribution of the probability of the results of observations to the laws of distribution of the probabilities of errors is reduced to replacing x with? in the formulas above.

error measurement setting

9. RANDOM ERRORS OF MEASUREMENTS

9.1 Sources of random errors

Random errors are called errors that are not defined in their magnitude and nature, in the appearance of which no regularity is observed.

Random errors are detected during repeated measurements of the desired quantity, since the results of individual measurements differ from each other even in cases where repeated measurements are carried out equally carefully and, it would seem, under the same conditions. In other words, random errors are unavoidable, and therefore the real value Xg is found with some approximation. Random errors include, for example, reading errors due to parallax (in instruments not equipped with a mirror scale). Depending on the location of the observer's eye, the end of the arrow seems to be located above one or another point on the scale, i.e. the actual reading obtained depends on the location of the eye (figure 9.1).

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The correct reference should be considered the point of the scale on which the arrow is projected, provided that the line of sight (from the pupil to the arrow) is perpendicular to the plane of the scale. Therefore, the reading is made at point a "displaced by some amount with respect to the true point a. In which direction and what value the parallax will be depends on the case. But how large the error is on average depends on the design of the device: the smaller the distance ratio h between the pointer and the scale to the total width of the scale, the smaller the average error.Therefore, the designer must take it into account in advance and take constructive measures to reduce it to an acceptable value.

The random error also includes the ocular error that occurs when determining the fraction of division by eye. When designing, it is usually believed that a person who has the necessary skill is mistaken in counting by no more than 1/10 of a division. This is provided that the scale meets certain requirements:

one). the divisions are not too small - at least 1.5 mm;

2). strokes are clear, not blurry;

3). the thickness of the strokes and the target line or thread, the thickness of the end of the arrow is convenient; usually recommend a stroke thickness of about 0.15 mm;

four). the color of the scale is such that the strokes stand out clearly;

5). at night, adequate illumination of the scale must be ensured.

The error (eye measurement or from parallax), expressed as a percentage, will be the smaller, the larger the scale (ie, the smaller the price of fine division).

As an example of a random error, one can also cite a temperature error, i.e. a change in the readings of the device due to the fact that the ambient temperature differs from the normal one at which the scale was calibrated. For this device, you can determine in advance how much the reading changes at a certain temperature increase. Therefore, it can be eliminated by taking into account the correction.

In most cases, random errors cannot be excluded empirically, but their influence on the measurement result can be theoretically taken into account by using probability theory and mathematical statistics when processing measurement results.

The normal distribution of random error (Gaussian distribution) obeys the equation

where is the probability of obtaining errors (frequency of occurrence of a random error).

The distribution functions can be quite fully defined by their numerical characteristics, which include the initial and central moments.

The initial moment of the k-order is the mathematical expectation of a random variable of degree k:

In most cases, the initial moment of the 1-order coincides with the true value of the measured quantity.

The central moment of the k-order is the mathematical expectation of the k-th degree of a centered random variable (ie the difference between the value of the random variable and its mathematical expectation). As applied to measurements, a centered random variable will be a random error:

X-M[X]=X-Q (9.3)

The central moment of the 2-order will be the variance of the results of the observations:

This is the dispersion of the results of observations relative to the mathematical expectation. The disadvantage of this representation of the measurement error is that it has the dimension of the square of the measured quantity. Therefore, in practice, the value of the standard deviation of the measurement result is used

Unlike measurement results, the numerical characteristics of the distribution function are deterministic, not random. Therefore, in order to find exact values, an infinite number of observations must be made. This gives rise to the problem of determining approximate values obtained in a certain number of independent observations. In mathematical statistics, such approximate values expressed as a single number are called point estimates. Any point estimate calculated on the basis of experimental data is a random variable that depends on the estimated parameter itself and on the number of experiments. The distribution of the estimate depends on the distribution of the original random variable. Grades are classified as follows:

Consistent, when, with an increase in the number of observations, they approach the value of the estimated parameter;

unbiased, if the mathematical expectation is equal to the estimated parameter;

effective if its variance is less than the variance of any other estimate of this parameter.

9.2 Point estimates of the numerical characteristics of the measured quantity

Let there be a sample of n measured quantities X1 X2, ... Xn. The measurement results contain only random errors. It is required to find an estimate of the true value of the measured quantity and a parameter characterizing the degree of dispersion of observations in a given sample.

9.2.1 Estimation of the true value of the measurand

With symmetric laws of probability distribution, the true value of the measured value coincides with its mathematical expectation, and the estimate of the mathematical expectation is the arithmetic mean of the results of individual observations:

9.2.2 Estimating the standard deviation (s.d.) of an observation

If the mathematical expectation of a random variable is known, then the rms. equals

If the mathematical expectation is unknown, then only an estimate of the mathematical expectation X can be found from the results of sample observations. This will be a consistent estimate, but biased.

The unbiased estimate will look like

9.2.3 Estimation of s.c.d. measurement result

The estimate of the true value of the measured quantity X obtained above is a random variable scattered with respect to Q. will look like this

This value characterizes the dispersion of the arithmetic mean value X of the results of n observations of the measured value relative to its true value.

9.3 Estimation of s.c.r. indirect measurement result

All of the above applies to the estimation of the s.c.d. direct measurement result. To estimate the s.c.d. the results of indirect measurement proceed as follows. Let the measurement result be a function of m variables Q = F(X1,X2,..,Xm). Find partial errors of the measurement result

where are the estimates of the r.c.d. the result of direct measurement of the i-value.

S.c.o. the result of indirect measurement is found by the formula

where Rij is the correlation coefficient showing the degree of statistical connection between particular measurement errors.

10. CLASSIFICATION OF MEASURING INSTRUMENTS

Of all the variety of methods and measuring instruments, we will consider only those that are widely used to measure the characteristics of electrical signals and parameters of radio circuits when monitoring the technical condition of various electronic devices. The measuring instruments used for this purpose can be conditionally divided into two groups: electromechanical and electronic measuring instruments.

Basic metrological characteristics of measuring devices

Instruments for monitoring the parameters of technological processes

Science deals with issues of the theory of measurements, means of ensuring their unity and ways to achieve the required accuracy. metrology.

Metrology defines measurement as a cognitive process, which consists in finding the relationship between the measured value and another value, conventionally accepted as a unit of measurement. So, if k is the measured value, a is the unit of measurement, and t is the numerical value of the measured value in the accepted unit, then

k = that. (2.1)

This equation is the basic measurement equation.

In the theory of measurements, there are: direct, indirect, cumulative and joint measurements.

Direct measurements, characterized by equality (2.1), consist in a direct comparison of the measured quantity with a unit of measurement using a measure or measuring device with a scale expressed in these units. Most of the physical quantities are determined not by direct measurements, but by calculations, using known functional dependencies.

Measurements in which the desired measured value is determined by calculations based on the results of direct measurements associated with the desired value by a known functional dependence are called indirect measurements. In this case, the value of the measured quantity is determined by the formula

Q = f(A,B,C, ...,), (2.2)

where A, B, C are the values obtained from direct measurements. Examples of indirect measurements are: determining the volume of a body by direct measurements of its geometric dimensions, the flow rate of a substance flowing in a pipeline, by a pressure drop across a throttle device, etc.

Cumulative measurements called those in which the desired values of quantities are found using a system of equations obtained by direct measurements of various combinations of these quantities.

Joint measurements are called simultaneous measurements of two or more dissimilar quantities to find the relationship between them.

2.1. Characteristics of measuring instruments

The measuring equipment includes measures, measuring instruments and auxiliary devices. By appointment, measures and measuring instruments are exemplary and workers.

Exemplary measures and measuring instruments are used to reproduce and store units of measurement, as well as to calibrate and verify working measuring devices.

Working measures and measuring instruments are intended for direct or indirect comparison of measured values with the corresponding units of measurement or measures and are divided into two groups - laboratory and technical. Laboratory measures and measuring instruments are characterized by a specified accuracy, and when they are used, the measurement result should be corrected in accordance with passport data, and the influence of external factors should also be taken into account. For technical measures and measuring instruments, the accuracy is assumed to be predetermined, and the measurement result, which is considered accurate within the limits of normalized metrological characteristics established by technical specifications or state standards, does not require any corrections.

In the general case, a measuring device is understood as a measuring tool designed to generate measurement information signals in a form accessible to direct perception by an observer. According to the method of issuing information, measuring instruments can be showing or registering, and in the presence of signaling devices - signaling.

Metrological characteristics measuring devices that determine the reliability of the information received, i.e. the main function of measuring instruments, serve as the main criteria for their quality. The standardized metrological characteristics of measuring instruments include the following indicators:

1. Measurement limits(in the form of a nominal static characteristic, the smallest division of a non-uniform scale of a measuring device, an output code or a nominal unit price).

2. Measurement accuracy standards(inaccuracies of measuring instruments, dynamic characteristics, sensitivity, stability and variation of indications, etc.).

3. Types, ways, expressions and methods of normalization of errors.

4. Methods of certification and testing.

The nominal static characteristic of the measuring instrument is understood as the functional dependence of the output signal (displacement of the reading device, etc.) on the measured parameter A (output signal) under given external conditions and in the steady state of the system. The static characteristic will be linear only if the differential sensitivity S is constant for the entire operating range of values A, when

S = = = const(2 3)

The minimum value X 0 of the measured value, which is capable of causing the smallest noticeable movement of the pointer or change in the output value, is called sensitivity threshold.

The constant of the device is understood as the number of units of measure by which the reading must be multiplied (the number determined by the position of the reading device) to obtain a reading in certain units of measure. In most measuring instruments, the reading devices are made in the form of a scale and a pointer. The scale is a set of marks located along a line. The beginning and end of the scale, corresponding to the lower and upper limits of measurement, determine the measurement range. The inertia of measuring instruments during the transition of a parameter from one steady value to another is estimated by dynamic characteristics, such as the time constant, the time for setting indications, etc. Accuracy is an important characteristic of measuring devices.

Measuring error device is called the difference between the measurement result X of a certain quantity and its actual value X 0:

A \u003d X - X 0, (2.4)

where A is the main quantitative characteristic of the measurement, called absolute error. Relative error, equal to the ratio of the absolute error to the actual value of the measured value, expressed as a percentage:

δ = 100/Ho

In this regard, the errors of measuring devices can be classified as follows:

static and dynamic, depending on the conditions and modes of operation;

systematic, random and gross, depending on the nature of their manifestation and the possibilities of elimination.

static error called the error that occurs at a steady value of the measured quantity and constant external conditions.

dynamic error called the error that occurs when the measured value and external influences change.

Systematic errors are called constant in magnitude and sign or varying according to a certain law of error, repeated during repeated measurements. Systematic errors are determined by repeated measurements of the same value under constant other conditions and are eliminated by means of adjusting devices or by introducing a correction using special elements. Systematic errors are divided into progressive and periodic. Continuously increasing or decreasing errors are called progressive. These include errors due to wear of parts, contacts, etc. Periodic errors are those that change in magnitude and sign and occur during the operation of measuring devices.

Random errors are errors that vary in magnitude and sign indefinitely. They determine the accuracy of the measuring device. Random errors are used to evaluate the accuracy of both the measuring devices themselves and the measurement methods. Due to a random error, the true value of the measured quantity is unknown, therefore, when calculating random errors, the measured value is taken as the arithmetic mean X of the obtained N measurements Xi,

2.1. Information characteristic of the measurement process

Any measurement can be considered as a chain of transformations of the measured quantity until the measurement result is presented in the form that was required to be obtained.

The measurement process is characterized by the transfer of information about the value of the measured quantity from one carrier to another, i.e. converting information about the value of the measured quantity into the measurement result. This means that in the informational aspect, measurement can be considered as the process of receiving and converting information from the measured quantity in order to obtain a quantitative result by comparison with the accepted scale or unit of measure in the form most convenient for further use by man and machine.

To establish a connection between the accuracy of measurements and the amount of information obtained during measurements, the basic provisions of information theory are used. However, under the term information"understand a set of information about an object, process or phenomenon, in the general case - about a physical system.

The task of obtaining information is to eliminate uncertainty in our ideas about the state of some physical system and to establish quantitative patterns associated with the receipt, processing and storage of information.

Thus, the receipt of any information, including measurement, is considered by information theory as the elimination of some uncertainty, and the amount of information is considered as the difference between the situation before and after receiving this message. At present, according to experts developing and using the information theory of measuring devices, the use of information theory methods will provide a more effective assessment of the quality of devices.

2.2. Supervision of measuring equipment

Ensuring the uniformity of measurements and maintaining measuring instruments in proper condition in all sectors of the national economy is carried out by a single metrological service of the country, headed by the State Standard of the Russian Federation and consisting of the state metrological service and departmental metrological services. The State Metrological Service has a number of research institutes and departments of the State Standard of the Russian Federation. The latter are in charge of territorial centers of metrology and standardization, interregional, regional (territorial) and interdistrict laboratories of state supervision of standards and measuring equipment.

The main tasks of the state metrological service are: - implementation of state supervision of measuring equipment,

Development of normative and technical documents of the state system for ensuring the uniformity of measurements (GSI) and control over their implementation,

Creation and improvement of the reference base and the park of exemplary measuring instruments,

GSI is a set of rules, regulations, requirements and norms established by state standards that determine the organization and methodology of work to assess and ensure the accuracy of measurements. These standards regulate: units of physical quantities, methods and means of reproducing these units and transferring their sizes to working measuring instruments, ways of expressing the normalized metrological characteristics of measuring instruments and indicators of the accuracy of measurement results; requirements for the measurement procedure; the procedure and methodology for conducting state tests, verification and revision of measuring instruments.

One of the main responsibilities of the state metrological service is to ensure state supervision of measuring equipment. The following are subject to supervision: production, condition, operation and repair of measures and measuring instruments, as well as the activities of departmental metrological services. Bodies of the State Standard of the Russian Federation have the right to prohibit the release into circulation of measuring instruments that do not meet the requirements of state standards and technical specifications, withdraw unsuitable measures and measuring instruments from circulation, carry out mandatory state verification of measuring instruments, and carry out state tests and certification of new measuring instruments.

All measures and measuring instruments intended for serial production and release into circulation are subject to state tests. In the process of testing, the conformity of devices to the needs of the national economy, the modern level of measuring technology and the requirements of standards is established. With positive results of state tests of devices, the State Standard of the Russian Federation allows their production and release into circulation and includes them in the state register.

To ensure the required accuracy of measurements, a certain procedure for organizing and conducting verification of measuring instruments has been established. All measuring instruments are subject to state or departmental verification.

The state verification performed by the system of the State Standard of the Russian Federation is subject to measuring instruments used in the bodies of the state metrological service, the original exemplary instruments used in the bodies of departmental metrological services, as well as working measuring instruments used for accounting and mutual settlements, ensuring safety, environmental protection and population health. The list of working measuring instruments subject to mandatory state verification, and the frequency of this verification for certain groups of instruments, are established by the State Standard of the Russian Federation.

Departmental verification is carried out by bodies of departmental metrological services of individual enterprises, organizations and institutions that have permission from the bodies of the State Standard of the Russian Federation to carry out verification work. All measuring instruments used in the national economy that are not covered by state verification are subject to this verification. Verification of measuring instruments is carried out in accordance with the requirements of State standards, instructions and guidelines of the State Standard of the Russian Federation for methods and means of verification. Devices recognized as a result of verification as not meeting their accuracy class or faulty are not allowed for further use until the identified deficiencies are eliminated. Appliances recognized as fit are stamped or certificates are issued. If necessary, restrict access to the mechanisms of devices. After their verification, the instrument cases are sealed.

When participating in state commissions for the acceptance of newly installed and reconstructed technological equipment of fire and explosion hazardous industries with the presence of automation, fire protection workers need to pay attention to compliance with the requirements of the relevant regulatory documents of the State Standard for verification of instruments and their branding. This reduces the possibility of fire and explosion situations at the facilities, and in the event of a fire and explosion, devices that have passed verification will objectively reflect the pre-emergency situation and the course of the accident that led to the fire.

DEVICES FOR CONTROL OF PARAMETERS OF TECHNOLOGICAL

PROCESSES

3.1. Temperature Instrumentation

To measure temperature, a change in some physical property of a body is used, which uniquely depends on its temperature and is easily measurable.

Among the properties underlying the operation of instruments for measuring temperature are: the volumetric expansion of bodies, the change in the pressure of a substance in a closed volume, the occurrence of a thermoelectromotive force, the change in the electrical resistance of conductors and semiconductors, the radiation intensity of heated bodies, etc.

Depending on the physical properties on which the operation of temperature measuring instruments is based, there are:

1. Expansion thermometers, built on the principle of changing the volume of a liquid or the linear dimensions of solids with a change in temperature. Are applied to measurement of temperature from-190 to +500 0 С.

2. Manometric thermometers based on the change in pressure of a liquid, gas or vapor in a closed volume with a change in temperature. They are used to measure temperatures from -120 to +600 0 С.

3. Thermoelectric pyrometers (thermocouples), the principle of operation of which is based on the occurrence of an electromotive force when the temperature of one of the junctions of a closed circuit of dissimilar thermoelectrodes changes. Are applied to measurement of temperature from-200 to +2000 0 С.

4. Resistance thermometers based on the change in the electrical resistance of a conductor or semiconductor with a change in temperature. Are applied to measurement of temperature from-200 to +650 0 С.

5. Radiation pyrometers operating on the principle of changing the radiation intensity of heated bodies depending on temperature changes. They are used to measure temperatures from +600 to +6000 0 С.

3.2. Pressure Instrumentation

Pressure is determined by the ratio of a force uniformly distributed over an area and normal to it, to the size of this area. Depending on the measured value, pressure measuring instruments are divided into:

pressure gauges - for measuring medium and large excess pressures;

vacuum gauges - for measuring medium and large rarefaction;

pressure and vacuum gauges - for measuring medium and large pressures and rarefactions;

pressure gauges - for measuring small excess pressures;

thrust gauges - for measuring small rarefaction;

thrust gauges - for measuring small excess pressures and

vacuums;

differential pressure gauges - for measuring the difference in pressure drop;

barometers - for measuring atmospheric pressure.

According to the principle of operation, the following devices for measuring pressure are distinguished: liquid, spring, piston, electrical radioactive.

liquid devices. In these devices, the measured pressure or rarefaction is balanced by the hydrostatic pressure of the column of the working fluid, which is used as mercury, water, alcohol, etc.

Spring devices. The measured pressure or rarefaction is balanced by the forces of elastic resistance of various sensitive elements (tubular spring, membrane, bellows, etc.), the deformation of which, proportional to the measured parameter, is transmitted by means of a system of levers to the arrow or pen of the device.

Piston gauges. The pressure is determined by the value of the load acting on a piston of a certain area, moving in an oil-filled cylinder; piston pressure gauges have high accuracy classes equal to 0.02; 0.05; 0.2 .

Electrical devices. The operation of these devices is based on measuring the electrical properties (resistance, capacitance, inductance, etc.) of some materials when exposed to external pressure.

Piezoelectric devices. These devices use the piezoelectric effect, which consists in the appearance of electric charges on the surface of certain crystals (quartz, Rochelle salt, tourmaline) when a force is applied to them in a certain direction.

radioactive devices. The pressure is determined by the change in the degree of ionization or the degree of absorption of y-rays with a change in the density of the substance.

3.3. Level Instruments

According to the principle of operation, level gauges for liquids are divided into pointing glasses, float, hydrostatic, electric and radioactive.

Indicating or level glass is a vertical glass tube in which the liquid, as in communicating vessels, is installed at the same height as in the apparatus. Index glasses are used for local level measurement in devices.

Float level gauges. In these devices, the sensitive element is a float with a lower (floating) or higher (submersible) specific gravity than the liquid. A change in the liquid level in the apparatus causes the float to move, which, with the help of a system of levers, rods and cables, is transmitted to a pointer moving along a scale, or to a secondary device for reading, recording.

Hydrostatic level gauges are used to measure the hydrostatic pressure of a liquid column, the level of which is being determined. There are hydrostatic piezometric and differential level gauges. The action of hydrostatic piezometric level gauges is based on the use of air or gas pressure bubbling through a liquid layer with a measured level when the latter changes.

The action of hydrostatic differential level gauges is based on determining the level by the pressure of the measured liquid column, which is balanced by the pressure of a constant liquid column.

Electrical level gauges. The most widely used level gauges are capacitive and ohmic.

In electric capacitive level gauges, the sensitive element is a capacitor, the plates of which are located on opposite sides of a vertical dielectric tube connected to the apparatus like communicating vessels. If one plate of the capacitor is an electrode, then the other is the wall of the apparatus. When the liquid level changes, the capacitance of the capacitor included in one of the arms of the AC bridge changes, and a signal proportional to the value of the measured level is applied to the input of the secondary device.

The action of electric ohmic level gauges used to determine the level of electrically conductive liquids is based on measuring the resistance between electrodes of the appropriate form inserted into the liquid. In this case, the resistance of the liquid layer between the electrode and the body or between two electrodes depends on the height of the liquid level in the apparatus.

Radioactive level gauges. The measurement of the liquid level is based on the measurement of the intensity of the absorption of y-particles when the liquid level changes.

3.4. Flow Instrumentation

Volume flow g is the volumetric amount of substance V that flows through the cross section of the pipeline per unit time t,

where p is the density of the substance, kg / m 3.

Instruments designed to measure flow are called flow meters, and those measuring the amount of a substance that flows through the cross section of a pipeline over a period of time are called counters.

According to the principle of operation, the flowmeters can be divided into flowmeters of variable and constant pressure drops, variable level.

Variable pressure drop meters. The operation of these devices is based on the occurrence of a pressure drop on a converging device of constant cross section installed inside the pipeline. The difference in static pressures before and after the converging device (pressure difference), measured by a differential pressure gauge, depends on the flow rate of the flowing substance and can serve as a measure of the flow rate.

Flow meters of constant differential pressure (rotameters). The action of these devices is based on the movement of a sensitive element (float) installed in a vertical conical tube; a substance is fed through it from below, the flow rate of which is measured. When the flow rate of liquid, gas or steam changes, the float moves up and the passage opening of the tube changes. The lift height of the float is functionally related to the flow rate. In this case, the pressure drop across the float while moving it along the axis of the tube remains almost constant.

Variable level flowmeters. The operation of these devices is based on a change in the height of the liquid level in the vessel with a continuous flow and free flow of it from the vessel.

There are other types of flow meters, the operation of which is based on certain physical laws (changes in electrical parameters, heat transfer to the flow, a decrease in the intensity of ultrasound or radioactive radiation depending on the flow rate).

3.5. Automatic Balanced Bridge

The balanced bridge is designed for continuous temperature measurement, recording and regulation. It works in conjunction with resistance thermometers with standard calibrations, i.e. corresponds to the specified measurement limit - the graduation of the resistance thermometer. This means that each device corresponds to a certain group of resistance thermometers of a single calibration. The essence of the operation of resistance thermometers is based on the dependence of its electrical resistance on temperature.

The principal measuring circuit of the device under consideration is a bridge. Measurements of non-electric quantities by electrical methods are very widespread in electrical engineering and automation. The bridge measuring circuit has been used for more than 100 years, and the ability to measure

The equilibrium condition means such a ratio of the bridge resistances, at which the potential difference Ubd = 0 at the vertices of the measuring diagonal and there is no output signal in the measurement circuit. The state U bd = 0 corresponds to the equality of the voltage drops, respectively, in the adjacent arms, i.e.

Ui = U4 and U2 = U3. (3.1)

Ohm's law

Ui = I1R1; U2 = I1R2; U3 = I2R3; U4 = I2R4. (3.2)

Substituting into the equality of voltage drops (3.1) their values expressed in terms of currents and resistances (3.2), and dividing term by term, we obtain:

I1R1/I1R2 = WI2R3 (3.3)

or, having reduced the values of currents I 1 and I 2 , we have the equality:

R1R3 = R2R4, (3.4)

which is called the classical equilibrium condition of the bridge circuit, read as follows: "If the products of the resistances of the opposite arms of the bridge circuit are equal to each other, then there is no potential difference at the vertices of the measuring diagonal." This method is called the null resistance measurement method.

The schematic diagram of the balanced bridge is shown in fig. 3.2.

A copper or platinum resistance thermometer R t , whose electrical resistance is to be measured, is included in one of the arms

bridge with the help of connecting wires having resistance R. The other arms of the bridge consist of constant manganin resistances Rmt and variable calibrated resistance of the reochord R p , also made of manangin. DC or AC power is supplied to one diagonal of the bridge, and a null indicator is switched on to the other. When the bridge is in equilibrium, the equality is satisfied:

R\Rt = R2R4, (3.5)

whence, taking into account the resistance of the reochord, we write:

(Rx+rx)Rt = (R2+r2)R4. (3.6)

In this case, the potential difference between the points bd is equal to zero, the current does not flow through the null galvanometer and its arrow will be set to zero. When the temperature changes, the electrical resistance of the resistance thermometer will change and the bridge will be unbalanced. To restore balance, it is necessary at constant resistances Ri, R 2 and R 4 to change the resistance value of the reochord by moving its movable contact.

Thus, if you calibrate the resistance of the reochord, then by the position of its slider when the bridge is in equilibrium, you can judge the value of the resistance R 1, therefore, the measured temperature.

Rice. 3.3. Schematic diagram of the electronic balance bridge

electrical resistance. The measuring bridge, consisting of constant and variable resistances (R 1, R 2 and R 4) and powered by voltage (6.3 V) from one of the windings of the power transformer, is unbalanced, and an unbalance voltage U appears in the diagonal of the bridge between points b and d bd. The latter is fed to the input of an electronic amplifier (EI), where it is amplified in voltage and power, then it enters the reversible RD engine and sets its rotor in motion. Rotating in one direction or another, depending on the sign of the unbalance, the rotor of the reversible motor moves the rheochord slider R p , the arrow and the pen, mechanically connected with it, along the instrument scale until the measuring bridge comes to a state of equilibrium. The voltage at the input of the electronic amplifier (EI) in this case will become equal to zero, the RD electric motor will stop, and the device will show the measured temperature.

The accuracy of the readings of the device depends on the adjustment of the resistance of the wires connecting the resistance thermometer to the automatic balance bridge. To adjust the resistance of the connecting wires to the calibration value, resistances R y and R "y are used, up to 2.5 ohms each. When calibrating devices, the resistance of each wire going from the thermometer to the device is taken to be (2.5 + 0.01) ohms. If the resistance of each wire will be less than 2.5 ohms, then an additional resistance is connected in series to the connecting line, adding the resistance of each wire to 2.5 ohms.

Under production conditions, the resistance thermometer can be located at a considerable distance from the secondary device, with fluctuations in the temperature of the medium, the value of their resistance will change, which will lead to an additional error in the readings of the automatic balance bridge. To eliminate the error, a three-wire connection diagram of the resistance thermometer with the secondary device is used, which consists in the fact that point c (Fig. 3.4) is transferred directly to the resistance thermometer. With this connection, the resistance

wire R is added to the arm of the measuring bridge, and the resistance

R to shoulder with constant resistance. Then the equilibrium condition of the bridge circuit will have the form:

(R1+rR1)(Rt+R l)) = (R2+rR 2 +R^)R4. (3.7)

The measuring circuit of the automatic balance bridge can also be powered by a dry DC battery or a battery with a voltage of 1.2-1.5 V. In this case, the electronic amplifier of the device must have a vibration transducer to convert the DC unbalance signal into AC for the purpose of its subsequent amplification.

In this regard, balanced DC bridges are used when various pickups may appear in the measuring circuit (for example, when installing a resistance thermometer in electric furnaces or places with high magnetic fields). In addition, DC bridges are used in cases where, due to the operating conditions of devices and fire safety, they are powered by low-power DC sources.

Structurally, an automatic self-recording balance bridge is a stationary device, all components of which are located inside a steel case. The readings are recorded on chart paper moved by a synchronous motor.

The industry produces automatic balance bridges showing and recording on a disk diagram, KCM2, KCM3, KCM4 bridges showing and recording on a tape diagram, showing bridges with a rotating scale and other modifications. Their schematic diagrams are similar to the considered scheme of an automatic equilibrium bridge and differ only in the design of individual nodes.

However, the type of electronic device discussed above also has a number of disadvantages:

small temperature measurement range (up to 600 0 С);

resistance thermometer installed in technological devices must be placed in the volume of the product;

the secondary device does not have special means of explosion protection and is installed only in the instrumentation and automation rooms.

3.6. Automatic potentiometer

The automatic potentiometer is designed to measure, record and control temperature. It works in a set with standard calibration thermocouples, it is used to measure temperatures from -200 to + 2000 0 C. As structural materials for thermocouple electrodes, iron-kopel, kopel-alumel, chromel-alumel, platinum-platinum-rhodium, etc. are used. Dependence thermoelectromotive force (TEMF) from temperature changes is linear.

In electronic potentiometers, a potentiometric (compensation) measurement method is used, which is based on balancing (compensating) the measured TEDS with a known potential difference formed by an auxiliary power source.

From the circuit diagram (Fig. 3.5) it can be seen that the thermocouple is connected so that its current in the section Rad goes in the same direction as from the power source B, and the potential difference between point A and any intermediate point D is proportional to the resistance Rad.

By moving the movable contact D, provided that Eju< Еб, можно найти такое его положение, при котором ток в цепи термопары будет равен 0, т.е. ТЭДС термопары может быть измерена значением падения напряжения на участке сопротивления RAд. Схема такого вида широко используется для измерения температуры в переносных приборах.

The disadvantage of the considered scheme is that TEDS depends on the constancy of the current in the reochord circuit.

Variation of the operating current in the rheo-chord circuit can introduce errors into the measurement results. Setting the required value of the operating current and monitoring its constancy is also carried out by the compensation method (Fig. 3.6).

The circuit has three circuits:

current source circuit (current source B, installation resistance, constant resistance, reochord with moving contact D);

circuit of a normal element (normal NE element, constant resistance, IP measuring device);

thermocouple circuit (TP thermocouple, IP measuring device, part of the variable resistance of the reochord).

In the control mode, the switch is set to position K, connecting the normal element to the ends of the resistance Rh.3 (the EMF of the power supply B is directed towards the EMF of the normal element). With a decrease in the magnitude of the operating current, it is regulated by a setting resistance and a position is reached at which the potential difference at the ends of the resistance Rh.3 does not become equal to the EMF of a normal element. The current in the meter circuit will become zero. If R ycT fails to establish the operating current, then the battery is replaced. In the measurement mode, the switch is set to position AND, thereby connecting the thermocouple in series with the normal element, the reochord at point A and the movable contact D. The TEMF of the thermocouple in this case will be directed in the opposite direction of the EMF of source B. By moving contact D, find its position, at which the potential difference between point A and the Dreochord contact is equal to the TEMF of the thermocouple.

In the devices of the GSP series, the measuring circuit is powered by a stabilized source, which simplifies the design and operation.

Metrology- the science of measurements, methods and means of ensuring their unity and the way to achieve the required accuracy.

Measurement- finding the value of a physical quantity empirically using special technical means and expressing the result in accepted units.

Dimension features:

The presence of a physical quantity

Experience required

Availability of a measuring instrument

Numerical value of a physical quantity

measuring tool- a measuring tool that has normalized technical characteristics.

Physical quantity- a property that is qualitatively common for many physical objects, processes or phenomena, but individual in quantitative terms.

The actual value of a physical quantity– the value that satisfies consumer tasks in this case.

PV classification.

Can do work: active, passive

deterministic, random

Analog - PV, which has an infinite number of values in a given range; quantized

In time: continuous, discrete

Measurement types .

Based on the result:

Direct - measurements in which the desired value is determined directly during the experiment

Indirect - uses a known functional relationship between the results measured in a direct way and the desired PV

Joint - simultaneous measurement of several different PVs is performed to find the relationship between them

Aggregate - measurements when several PVs of the same name are simultaneously measured to determine the desired values of another PV

Based on change over time:

Static - measurement of the value of some PV, the value of which is unchanged during the time the result is used

dynamic

On the basis of the multiplicity of measurement:

Single

Multiple

Based on accuracy

Equivalent - constant conditions are provided, the same measuring instruments

Unequal - different in terms of accuracy of measuring instruments.

Information– information that reduces a priori uncertainty about the object.

Measurement information signal– signal, the parameters of which are functionally related to the measured value.

The informational aspect of the measurement: obtaining any SIS is a chain of signal transformations.

measuring tool- technical means with standardized metrological characteristics.

The carrier of the PV is the signal.

Signal is a physical process that takes place over time.

Integral characteristics:

- crest factor

- forms

- gains

- sinusoidal

1,1,1 - meander

- sawtooth

Classification of measuring instruments.

Measures - measuring instruments that reproduce PV of a given size

Measuring transducers are means of measurement that provide IS in a form that is convenient for transmission, storage, processing, but inconvenient for direct perception by an observer. Thermocouple. An electrical value into an electrical one (transformer). Not electrical to electrical. Generator (thermocouple). Parametric (resistance thermometer) do not generate a signal, an additional power supply is required for operation. The sensor is a structurally designed measuring transducer.

Measuring devices are means of measurement that produce SIS in a form convenient for direct perception by the observer. Analog, digital. The analog output value is a continuous function of the input value. Depending on the possibility of preserving the results, they are divided into showing and recording. Depending on the installation site, stationary and portable are distinguished.

Measuring setups - a set of structurally and functionally integrated measuring instruments and auxiliary devices, designed for the rational construction of a measuring experiment.

Measuring system - a set of structurally and functionally integrated measuring instruments and auxiliary devices, designed to automatically collect measuring information from a number of objects with subsequent transmission, processing, storage.

K - switch

PNK - voltage-to-code converter

CS - communication channel

M - modulator

DM - demodulator

Measurement methods .

Depending on the use of the measure:

Method of direct assessment - measures are not involved in the measurement process, the result is obtained directly on the reading device of the measuring instrument. The measure is used indirectly - in the manufacture of the device.

Comparison methods - the measure is directly involved in the measurement process

Zero method.

NI - zero indicator

Ex - measured voltage

U0 - exemplary measure

The method lies in the fact that the difference between the measured value and the value reproduced by the measure is reduced to 0 during the measurement process, which is fixed by the NI. The result is equal to the value of the measure. Bridge measuring devices. With a high accuracy of the measure, the method allows you to obtain a measurement result with high accuracy.

Differential Method.

The difference between the quantity being measured and the quantity reproduced by the measure is measured using a measuring instrument. The result is obtained as the sum of the value of the measure and the readings of the measuring instrument. This method allows you to obtain a measurement result with high accuracy when using a measuring instrument of relatively low accuracy.

Δ is the absolute error of the voltmeter.

substitution method.

There is an alternate measurement of the measured value and the value reproduced by the measure. The value of the unknown quantity is determined from these two measurements. It has sufficient accuracy if the object of measurement is approximately equal to the measure.

Measurement errors .

Error- quantitative characteristic

Accuracy is a qualitative characteristic reflecting the closeness of the error to zero.

Classification.

By way of expression:

According to the place (cause) of occurrence:

Methodical - due to the inadequacy of the accepted model of the object of measurement

Instrumental - instrumental error of the measuring instrument itself

By the nature of the change:

Systematic - constant or changing according to a known law

Random - changes according to the laws of random numbers. To find it, elements of probability theory, statistical measurements

Misses - the subjective error of the operator

By the way the environment influences the measuring instrument:

Main - occurs under normal operating conditions of the measuring instrument

Additional - in conditions other than normal

By the nature of the change over time:

Static - occur when measuring a constant value in time

Dynamic - when measuring a signal that changes with time

In connection with the measured value:

Additive - does not depend on the measured value

Multiplicative - depends on the measured value

Characteristics of measuring instruments .

Non-metrological– characteristics that do not affect the accuracy of the measurement result (weight, size, color).

Metrological– affect accuracy (input resistance, capacitance, friction, etc.)

Basic metrological characteristics:

The nominal static conversion function is the relationship between the information parameters of the input and output signal. Entered for the type of measuring instrument.

The actual transformation function (transformation equation) is the actual characteristic of the transformation. In the form of a functional dependence, a table of input and output values, functions in coordinates.

Sensitivity is the ratio of the increment of the output value to the increment of the input value that caused this increment.

Sensitivity threshold (resolution) - the minimum value of the input value, which can be detected by changing the output value.

Instrument constant - the ratio of some value of the measured value to the instrument reading in divisions.

The division price is the difference between adjacent scale marks, and if this difference is a constant value, then the scale is uniform.

Reading ranges - the difference between the maximum and minimum values.

Measuring ranges - the area on the scale of the measuring instrument, in which metrological characteristics are determined (set) - operating range

Characteristics of the measuring instrument that affect the measuring circuit.

Errors of the measuring instrument. Basic, additional. Additive, multiplicative.

Normalization of the error of the measuring instrument .

Accuracy class of measuring instrument- the main integral metrological characteristic of the measuring instrument, which gives the limit of the main error. In some cases, the accuracy class specifies both additional errors and other metrological characteristics. The value of the accuracy class is chosen from some number series:

For electronic oscilloscopes, the accuracy class reflects a different value.

Rationing- setting the nominal characteristic for a given type of measuring instrument and permissible deviations for a given result.

Type of measuring instrument- a set of measuring instruments of the same purpose, based on the same principle, having the same design and made according to the same technological documentation.

The method of normalizing the error of a measuring instrument depends on the nature of the absolute error of this instrument.

The error is additive.

on a uniform scale.

with a checkmark at the bottom. With an uneven scale.

Multiplicative nature of the error.

in a circle.

Mixed nature of error.

Verification- this is a clarification of the compliance of a given measuring instrument with its accuracy class.

Normalization of additional error.

Normalization of the additional error is reduced to setting the influence coefficient or influence function.

Electromechanical devices .

These are devices in which the electrical energy of the measured signal is converted into mechanical energy of the moving part of the device.

Measuring chain- serves to convert the electrical energy of the input signal into the same electrical energy (scaling)

measuring mechanism- to convert electrical energy into mechanical movement of the moving part.

Reading device- for visualization.

Classification of electromechanical devices.

By type of measured value (current, voltage, resistance, power, frequency, phase)

According to the type of electrical signal

According to the method of creating a counteracting moment (mechanical - spring, ratiometric - due to an additional coil that creates a counter magnetic field)

According to the method of calming the moving part (magnetic induction, air, liquid)

By type of measuring mechanism (magneto-electric, electro-magnetic, electro-dynamic, electro-static, induction, ferro-dynamic)

Magneto-electric devices.

Magnetic pole pieces, fixed core, current loop, counter spring.

The field in the gap is uniform.

Advantages:

Flaws:

Low overload capacity

Inability to work on alternating current

Relative complexity of production

Devices based on MEIM .

Ammeters.

Voltmeters.

Ohmmeters.

Sequential scheme.

The influence of the power supply on the measurement result is removed using a magnetic shunt built into the design of the IM, which affects the magnetic field to compensate for the supply voltage.

Parallel circuit.

Advantages:

High accuracy

High reliability

Disadvantage: dependence on supply voltage.

It is possible to build combined instruments (testers) that simultaneously measure voltage, current, resistance (inductance, capacitance). On the basis of MEIM, such highly sensitive devices as galvanometers, as well as devices for measuring on alternating voltage, are also built.

Electronic analog instruments and converters .

Measuring instruments in which the measurement information signal is converted using analog electronic devices. The output signal of such measuring instruments is a continuous function of the input signal. Used to measure all kinds of electrical signals: voltage, current, resistance, phase, frequency…

Electronic voltmeters- measuring instruments in which the measured voltage is converted into direct current, which is measured by MEIM.

Characteristics:

Wide voltage measurement range, from 10^-9V DC to 10^3V AC.

High sensitivity due to the use of input amplifiers

Large input impedance

Wide frequency range of measured voltage from 0 to 10^8 Hz

The uneven frequency response should not exceed ±3 dB relative to the reference.

Electronic voltmeters are divided into:

Direct current

Alternating current

Universal (also measure additional quantities)

Pulse

selective

Electronic DC Voltmeters.

Input divider, DC amplifier, Measuring mechanism.

They have high sensitivity.

Peculiarities:

At
zero level drift appears.

To increase the sensitivity, a modulator, demodulator is used.

The function of the modulator and demodulator is performed by analog keys, which are controlled by the generator synchronously. Allows you to get the value of the gain up to ~ 10 ^ 5. Depends on polarity.

AC Voltmeters.

Depending on the converter:

Peak values

Average values

Valid values

Peak detectors- converters in voltmeters of amplitude values.

Peak detector with open input.

The capacitor is charged with a positive half-wave, the negative half-wave is not passed by the diode. To minimize ripples, the charge-discharge time of the capacitor is selected.

Peak detector with closed entrance.

Due to scaling in r.m.s.
, the crest factor of the sinusoidal signal. If not a sinusoidal signal, then

Average Voltmeters.

AC voltage amplifier, converter.

Increasing the input voltage increases the sensitivity and reduces the effect of the nonlinearity of the input diodes of the converter (due to the transition to the region of linear dependence)

for a non-sinusoidal signal.

Squarers are used to amplify the signal.

. The scale of such devices is quadratic.

Universal voltmeters.

Based on closed entry peak detectors.

DC voltage: 0.1÷600V

AC voltage: 1÷600V

Resistance: 10Ω÷100MΩ

Pulse voltmeters.

For measuring the amplitude of signals of various shapes.

Peculiarities:

The scale is graduated in amplitude values. Peak detector with closed entrance.

Selective voltmeters.

To measure the effective voltage values in a certain frequency band or the effective value of certain harmonics.

Passes one frequency. The effective value of the signal for a real voltmeter. Low accuracy 6÷15% basic error. 0.1μV÷1V. 10Hz÷100kHz.

cathode ray oscilloscope .

For visual observation, measurement and recording of electrical signals.

Peculiarities:

Wide frequency range

High sensitivity

Large input impedance

Cathode-ray tube.

K - cathode: electron emission.

A1, A2 - anodes.

A1 - focus: line thickness

A2 - accelerating anode.

UGO - horizontal deflection amplifier. UVO - vertical.

A3 - measurement of impulse signals of a large duty cycle.

Characteristics:

Sensitivity

Bandwidth

Afterglow duration - the time between the termination of the beam and the moment when the brightness reaches 1% of the original

Screen working area: geometric dimensions and non-linearity of beam deflection.

Generalized oscilloscope structure.

ID - input divider - input signal scaling

PU - starting device - launching the vertical deflection channel

LZ - delay line - to delay the input signal for some time, the response time of the GR

VU - output amplifier - for generating a signal that controls directly the vertical deflection plates.

VVO - vertical deflection amplifier

KA - amplitude calibrator - a generator of rectangular pulses with known amplitude and frequency values. Thus, during calibration, the normalized values of the amplitude and frequency are set, according to which the deviation and sweep coefficients are adjusted.

CD - duration calibrator

BS - synchronization block - to obtain a stable picture, for which the GR frequency is made variable

GR - sweep generator - sawtooth signal formation

UGO - horizontal deflection amplifier

Error normalization.

4 accuracy classes: 1(3%), 2(5%), 3(10%), 4(12%) - for Co and Kd.

This error is normalized when normalized signals (meander or sine) are applied to the oscilloscope input.

If the period of the observed signal is a multiple of the GR frequency, then we see a stationary picture. LZ is used to compensate for the shift time.

Standby and automatic synchronization: in the standby mode, the GR starts only at the same time as the observed signal arrives.

Closed input - only the variable component passes, Open - constant too.

Digital measuring devices .

These are devices that automatically generate discrete signals of digital information and the readings are presented in digital form.

Produces a digital code in accordance with the measured value, while the continuous analog value is quantized in level and sampled in time.

Discretization in time– a transformation in which the value of a quantity differs from 0 and coincides with the corresponding value of the measured quantity only at certain points in time. The intervals between these values are the sampling step.

Level quantization– a transformation in which a continuous analog value takes on fixed, quantized values. These values are quantization levels or quanta.

An important characteristic is the rule for identifying the measured quantity and quantization levels.

Basic methods for converting a continuous value into a code.

Sequential counting method- has the maximum measurement time, but the cheapest.

Successive approximation method Each next step is half of the previous one.

Reading method– simultaneous comparison of the measured value with all quantization levels at once. The measurement time is the smallest, but expensive.

CIU classification .

According to the method of transformation:

consecutive count

successive approximation

readings

By type of measured value

According to the method of averaging the measured value:

instantaneous values

averaging (integrating)

By mode of operation:

cyclic action (according to a rigid program)

tracking - track changes in the quantizing value by a certain value

CIU=ADC+OU, CPU=DAC+ADC

Main metrological characteristics of TsIU.

Static:

discreteness (quantization) error

sensitivity

implementation of quantization levels

from interference

Discretization error.

Quantization error - methodical. Systematic - checkmate expectation.

Sensitivity error. Occurs as a result of the imperfection of the comparing device.

Error from the implementation of quantization levels.

Δd – methodical; Δh, Δr - instrumental

If the shift of quantization levels depends on the level number, then the error
.

The error arising from the quantization of the time interval. When measuring the time interval, quantizing pulses of a known frequency are used.

Errors from the time shift of the start and stop pulses relative to the quantizing one.

The start pulse is synchronized with half the period of the quantizing pulse.

Accuracy class c/d.

Time-pulse digital voltmeter .

The measured Ux is converted into a time interval Tx, which in turn is measured by quantization with pulses of a stable frequency f0 and by counting these pulses over time tx is converted into a code.

The angle of inclination Uk or the rate of its formation are known.

Source of errors of VCVV.

Dynamic errors TsIU .

- dynamic error of the first kind, due to the aperiodic properties of the input circuit.

Let the conversion of an analog value into a quantized one be carried out by the method of sequential counting.
determined by the conversion time.

Where M1 is the module of the maximum of the first derivative of the signal - the rate of its change.

MINISTRY OF COMMUNICATIONS OF THE RUSSIAN FEDERATION

MOSCOW STATE UNIVERSITY OF COMMUNICATIONS (MIIT)

Department of Electrical Engineering, Metrology and Power Engineering

G.G. Ryabtsev, I.V. Semenov

APPROVED by the editorial and publishing board of the university

METROLOGICAL CHARACTERISTICS OF ELECTRO-MECHANICAL MEASURING INSTRUMENTS FOR DIRECT EVALUATION

Guidelines for laboratory work on metrology for students of electrical engineering specialties

Moscow - 2004

UDC 621.317.39(075.8)

Ryabtsev G.G. Semenov I.V. Metrological characteristics of electromechanical measuring instruments of direct evaluation: Guidelines for laboratory work. – M.: MIIT, 2004. – 24 p.

Brief theoretical information about the metrological characteristics of electromechanical measuring devices for direct evaluation is given, examples of calculating the characteristics of devices and choosing devices for measurements are given, taking into account the characteristics of the electrical quantities measured by them.

1. PURPOSE OF THE WORK

Study of the metrological characteristics of electromechanical devices for direct evaluation.

2. THEORETICAL BRIEF

a device in which the reading of the measurement result is carried out directly on a scale calibrated in units of the value measured by the device.

Metrological characteristics are the characteristics of the device,

determining its suitability for measuring a certain physical quantity in a given range of its values and with a given accuracy.

Metrological characteristics of measuring instruments are divided into static and dynamic.

Static characteristics determine the properties of the device when measured by it steady state desired value. The static characteristics of the device include: conversion function, indication and measurement ranges, sensitivity, scale division, input resistance, power consumption and accuracy class.

Dynamic characteristics determine the properties of the device when measuring it time-varying quantities. Dynamic characteristics include: amplitude-frequency response, transient response and dynamic error of the device.

2.1. Instrument Conversion Function

The conversion function (or equation) of the instrument is output dependency instrument signal from the value measured by it

input signal

For electromechanical measuring instruments of direct evaluation, this is the dependence of the angle α of deviation (in divisions of the instrument scale) of the arrow of the reading device of the instrument on the level X of the value measured by it.

α = f(X ).

Instrument conversion functions are presented in the form of analytical dependencies, graphs, tables. The conversion function of the device is used to build the calibration characteristics of its scale. The ideal conversion function is a linear relationship (in this case, the scale of the instrument is uniform, which provides a more accurate reading of the measurement result).

2.2. Indication range and measurement range of the instrument

The range of indications is the range of values of the instrument scale, limited by the initial and final marks of the scale.

The measurement range is the range of values of the measured quantity, in

within which permissible error limits are normalized

In instruments with a linear conversion function and a uniform scale, the reading range and the measuring range are the same.

In devices with a non-linear conversion function and an uneven scale, the measurement range is marked on the scale with dots or a solid line drawn under the scale marks (Fig. 1).

The smallest value of the measured quantity in the measurement range is called the lower measurement limit, and the largest value is called the upper measurement limit.

Xmax

αmax

2.3. Instrument sensitivity

The sensitivity of a measuring device characterizes the ability of the device to respond to changes in the input signal. Sensitivity is determined from the conversion equation and is the ratio of the signal change Δα at the device output to the change X of the signal at the device input

The sensitivity of devices with an uneven scale has different values at different points of the scale and for each point is determined by relation (2).

2.4. The price of division of the scale of the device

The division price of the scale of a pointer measuring device is the difference in the values \u200b\u200bof the quantities corresponding to two adjacent marks on the scale, it determines the scale of the reading device device.

The division price of a uniform scale is defined as the ratio

top	Xmax	measurable		instrument	quantities
the corresponding number of divisions α max of its scale
		C =	Xmax
		C =
			α max

For example, for a milliammeter from paragraph 2.3. the division value will be C = 1 mA.

The division value of the non-uniform scale of the device is determined at each point as the difference between the values of the measured quantity corresponding to two adjacent scale marks.

2.5. Input impedance and power consumption of the device

Input impedance and power consumption determine

degree of influence measuring device on working mode

electrical circuit in which the measurement is made. For example, the lower the input resistance of the voltmeter, the more it decreases

voltage drop in the section of the circuit in parallel to which this voltmeter is connected, since the equivalent resistance of the circuit, determined by the resistance of the section of the circuit and the voltmeter connected in parallel, decreases. Therefore, voltmeters should have as much resistance as possible. Unlike voltmeters, ammeters should have as little input resistance as possible, since they are connected in series in an electrical circuit and increase the resistance of this circuit, as a result of which the current in it decreases.

The input resistance of the device is indicated in its passport, and if it is not indicated, then it is determined by calculation.

To calculate the input resistance of the voltmeter, the upper limit U max of the voltage measured by it and the corresponding value I max of the current flowing through the voltmeter (total deflection current) are used.

To calculate the input resistance of the ammeter, use the upper limit I max of the current measured by it and the corresponding voltage drop U max on the ammeter. The values of the total deviation current for voltmeters and the voltage drop for ammeters are indicated in their passports, and in some types of devices (including M2038 and AVO-5M1) they are indicated on the scale. According to the specified values, the input impedance

instrumentation is calculated according to Ohm's law
	Umax

	Imax

The input resistances of electromechanical voltmeters range from several units to tens of thousands of ohms, and ammeters - from hundredths to tenths of ohms.

The maximum value of the power consumed by the device is found from the above values of its current and voltage

Pmax=Umax× Imax,

or according to the limit of the value measured by the device and its input resistance. For example, for a voltmeter

			Umax2

	V. max		R V. in
			R V. in
and for ammeter
				×R	A. in
	A. max				A. in
Consumed	power		electromechanical			appliances
insignificant (from hundredths -		to units of watts). The best is considered
device with lower power consumption.

For ohmmeters, the input resistance and power consumption are not set, since ohmmeters measure the resistance of a de-energized circuit. Therefore, ohmmeters do not draw power from the circuit in which measurements are taken, and the indicated characteristics for them do not make sense.

2.6. Instrument accuracy class

Accuracy class defines guaranteed borders, beyond which the error of the device does not go in the measurement range established for it.

Accuracy class K T of electromechanical pointer measuring instruments is normalized as a percentage of the limit D X max

(guaranteed borders) the absolute error of the device to

normalizing value X NORM of its scale

CT	D Xmax	× 100%.

	X NORM

normalizing value X NORM for devices with a uniform scale is the upper limit of the value measured by the device, and for devices with

uneven scale - the length of its working part, i.e. the length of the section between the scale marks corresponding to the measuring range of the device.

For electromechanical pointer measuring instruments, the following numbers of accuracy classes are established: 0.05; 0.1; 0.2; 0.5 (for laboratory instruments) and 1; 1.5; 2.5; 4 (for technical devices).

The accuracy class number of the device is indicated on its scale. For devices with a uniform scale, this figure is indicated without any signs (circles, squares, asterisks), for example, 2.5. For devices with an uneven scale, the figure of the accuracy class is underlined by a broken line

line, for example, 2.5 .

According to the formula (9), the accuracy class of the device is evaluated maximum allowable the value of its absolute error. Such an assessment is necessary to determine the error of the measurement result performed by the device, as well as to select a device that provides the required measurement accuracy.

Calculation of the absolute error limit of the device with uniform scale held directly according to the formula (9) of the accuracy class, and for devices with uneven scale according to formula (9), first, the error of the instrument is determined in units (mm) of the scale length, and then according to it and scale division the absolute error is calculated in units of the measured value.

Example 1. Determine the limit I max of the absolute error of the ammeter, which has a uniform scale, the upper limit of the measured current I max \u003d 5 A and the accuracy class K T \u003d 1.

Solution 1. The device has a uniform scale, therefore, the normalizing value in the formula (9) of its accuracy class is the upper limit of the measured current I max \u003d 5 A.

The absolute error limit of the ammeter is found directly from formula (9)

DI max = ±K T × I max = ±1 × 5 = ±0.05 A.

Example 2. Determine the limit D R max of the absolute error of an ohmmeter with an uneven scale at its three points (beginning, middle and end of the scale), if the measuring range of the device lies in the range from 3 to 300 kOhm, the length of the working section of the scale (i.e. between the marks 3 and 300)

is L R \u003d 60 mm, accuracy class K T \u003d 2.5, division value (in mm) of the scale in

the beginning, middle and end of the working section of the scale, respectively, is equal to,

and C

Solution 2. According to the formula (9), the accuracy class of the ohmmeter is determined

limit D L msx

its absolute error, expressed in units of length

K T × L P

Limit D R max absolute error of the ohmmeter

units

measured value (i.e. in kOhm) is found by value

D L msx and price

From the division of the instrument scale at the corresponding point on the scale

DR = DL×C = ±

K T×L P×C

From here we find

2.5×60×0.1

= ± 0.15kΩ;

max.n

2.5×60×1

= ± 0.15kΩ;

max.n

2.5×60×10

= ± 0.15kΩ.

max.n

Example 3. Determine the limits of the absolute D I max and relative

δmax

errors in the result of measuring the current with an ammeter,

which one

9. Measuring instruments and their characteristics

In the scientific literature, technical measuring instruments are divided into three large groups. These are: measures, calibers and universal measuring instruments, which include measuring instruments, control and measuring instruments (CIP), and systems.

1. A measure is a measuring instrument that is intended to reproduce the physical quantity of the prescribed size. Measures include plane-parallel length measures (tiles) and angular measures.

2. Calibers are some devices, the purpose of which is to be used to control and search within the required boundaries of dimensions, the relative positions of surfaces and the shape of parts. As a rule, they are divided into: smooth limit gauges (staples and plugs), as well as threaded gauges, which include threaded rings or staples, threaded plugs, etc.

3. Measuring device, presented in the form of a device that generates a signal of measuring information in a form understandable for the perception of observers.

4. Measuring system, understood as a certain set of measuring instruments and some auxiliary devices that are interconnected by communication channels. It is designed to produce measurement information signals in a form that is suitable for automatic processing, as well as for translation and use in automatic control systems.

5. Universal measuring instruments, the purpose of which is used to determine the actual dimensions. Any universal measuring tool is characterized by its purpose, principle of operation, i.e. the physical principle underlying its construction, design features and metrological characteristics.

In the control measurement of angular and linear indicators, direct measurements are used; relative, indirect or cumulative measurements are less common. In the scientific literature, among direct measurement methods, as a rule, the following are distinguished:

1) direct assessment method, which is a method in which the value of the quantity is determined by the reading device of the measuring device;

2) method of comparison with a measure, which is understood as a method in which a given value can be compared with the value reproduced by the measure;

3) the method of addition, which is usually understood as a method when the value of the obtained value is supplemented by a measure of the same value so that the instrument used for comparison is affected by their sum equal to a predetermined value;

4) differential method, which is characterized by measuring the difference between a given value and a known value, a reproducible measure. The method gives a result with a fairly high accuracy rate when using rough measuring instruments;

5) the zero method, which, in essence, is similar to the differential method, but the difference between the given value and the measure is reduced to zero. Moreover, the zero method has a certain advantage, since the measure can be many times smaller than the measured value;

6) substitution method, which is a comparative method with a measure, in which the measured value is replaced by a known value, which is reproduced by the measure. Recall that there are also non-standardized methods. This group typically includes the following:

1) the method of opposition, which implies a method in which the given value, as well as the value reproduced by the measure, at the same time act on the comparison device;

2) the coincidence method, characterized as a method in which the difference between the compared values is measured using the coincidence of marks on the scales or periodic signals.

10. Classification of measuring instruments

Measuring instrument (SI)- this is a technical tool or a set of tools used to carry out measurements and has normalized metrological characteristics. With the help of measuring instruments, a physical quantity can be not only detected, but also measured.

Measuring instruments are classified according to the following criteria:

1) according to the methods of constructive implementation;

2) according to metrological purpose.

According to the methods of constructive implementation, measuring instruments are divided into:

1) measures of magnitude;

2) measuring transducers;

3) measuring instruments;

4) measuring installations;

5) measuring systems.

Measures of magnitude- these are measuring instruments of a certain fixed size, reused for measurement. Allocate:

1) unambiguous measures;

2) multivalued measures;

3) sets of measures.

A number of measures, technically representing a single device, within which it is possible to combine the existing measures in different ways, is called a store of measures.

The object of measurement is compared with the measure by means of comparators (technical devices). For example, a balance scale is a comparator.

Standard samples (RS) belong to unambiguous measures. There are two types of standard samples:

1) standard samples of the composition;

2) standard property patterns.

Reference material for composition or material- this is a sample with fixed values of quantities that quantitatively reflect the content in a substance or material of all its constituent parts.

A standard sample of the properties of a substance or material is a sample with fixed values of quantities that reflect the properties of a substance or material (physical, biological, etc.).

Each standard sample must necessarily pass metrological certification in the bodies of the metrological service before it can be used.

Reference materials can be applied at different levels and in different areas. Allocate:

1) interstate SOs;

2) state SOs;

3) industry SS;

4) SO of the organization (enterprise).

Measuring transducers (IP)- these are measuring instruments that express the measured value through another value or convert it into a signal of measuring information, which can later be processed, converted and stored. Measuring transducers can convert the measured value in different ways. Allocate:

1) analog converters (AP);

2) digital-to-analog converters (DAC);

3) analog-to-digital converters (ADC). The measuring transducers can occupy different positions in the measurement chain. Allocate:

1) primary measuring transducers that are in direct contact with the measurement object;

2) intermediate measuring transducers, which are located after the primary transducers. The primary measuring transducer is technically isolated; signals containing measuring information enter the measuring circuit from it. The primary measuring transducer is a sensor. Structurally, the sensor can be located quite far from the next intermediate measuring instrument, which should receive its signals.

Mandatory properties of the measuring transducer are normalized metrological properties and entry into the measurement circuit.

Measuring device is a means of measurement by means of which the value of a physical quantity belonging to a fixed range is obtained. The design of the device usually contains a device that converts the measured value with its indications into an optimally easy-to-understand form. To output measuring information, the design of the device uses, for example, a scale with an arrow or a digital indicator, through which the value of the measured value is recorded. In some cases, the measuring device is synchronized with a computer, and then the measurement information is output to the display.

In accordance with the method for determining the value of the measured quantity, the following are distinguished:

1) direct action measuring instruments;

2) measuring instruments for comparison.

Direct acting measuring instruments- these are devices by means of which it is possible to obtain the value of the measured quantity directly on the reading device.

Comparison measuring device is a device by means of which the value of a measured quantity is obtained by comparison with a known quantity corresponding to its measure.

Measuring instruments can display the measured value in different ways. Allocate:

1) indicating measuring instruments;

2) recording measuring devices.

The difference between them is that with the help of an indicating measuring device, it is only possible to read the values of the measured value, and the design of the recording measuring device also allows recording the measurement results, for example, by means of a diagram or drawing on some information carrier.

Reading device- a structurally isolated part of the measuring instrument, which is intended for reading readings. The reading device can be represented by a scale, pointer, display, etc. Reading devices are divided into:

1) scale reading devices;

2) digital reading devices;

3) registering reading devices. Scale reading devices include a scale and a pointer.

Scale- this is a system of marks and their corresponding sequential numerical values of the measured quantity. The main characteristics of the scale:

1) the number of divisions on the scale;

2) division length;

3) division price;

4) indication range;

5) measurement range;

6) measurement limits.

Scale division is the distance from one mark on the scale to the next mark.

Division length- this is the distance from one axial to the next along an imaginary line that passes through the centers of the smallest marks of this scale.

Scale division value is the difference between the values of two neighboring values on a given scale.

Dial Range is the range of values of the scale, the lower limit of which is the initial value of the given scale, and the upper one is the final value of the given scale.

Measuring range is the range of values within which the normalized maximum permissible error is established.

Measurement limits is the minimum and maximum value of the measuring range.

Almost uniform scale- this is a scale in which the division prices differ by no more than 13% and which has a fixed division price.

Significantly uneven scale is a scale in which the divisions are narrowed and for divisions of which the value of the output signal is half the sum of the limits of the measuring range.

There are the following types of scales of measuring instruments:

1) one-sided scale;

2) two-sided scale;

3) symmetrical scale;

4) zero-free scale.

One-sided scale is a scale with zero at the beginning.

double sided scale is a scale in which zero is not at the beginning of the scale.

Symmetric scale is a scale with zero in the center.

Measuring setup- this is a measuring instrument, which is a set of measures, IP, measuring instruments, etc., performing similar functions, used to measure a fixed number of physical quantities and collected in one place. If the measuring setup is used for product testing, it is a test bench.

Measuring system- this is a measuring instrument, which is a combination of measures, IP, measuring instruments, etc., performing similar functions, located in different parts of a certain space and intended to measure a certain number of physical quantities in this space.

According to the metrological purpose, measuring instruments are divided into:

1) working measuring instruments;

2) standards.

Working measuring instruments (RSI) are the measuring instruments used to carry out technical measurements. Working measuring instruments can be used in different conditions. Allocate:

1) laboratory measuring instruments that are used in scientific research;

2) production measuring instruments that are used in the control over the course of various technological processes and product quality;

3) field measuring instruments that are used during the operation of aircraft, vehicles and other technical devices.

Certain requirements are imposed on each individual type of working measuring instruments. The requirements for laboratory working measuring instruments are a high degree of accuracy and sensitivity, for industrial RSI - a high degree of resistance to vibrations, shocks, temperature changes, for field RSI - stability and proper operation in various temperature conditions, resistance to a high level of humidity.

Standards- these are measuring instruments with a high degree of accuracy used in metrological studies to transmit information about the size of a unit. More accurate means of measurement transmit information about the size of the unit, and so on, thus forming a kind of chain, in each next link of which the accuracy of this information is slightly less than in the previous one.

Information about the size of the unit is transmitted during the verification of measuring instruments. The verification of measuring instruments is carried out in order to approve their suitability.

11. Metrological characteristics of measuring instruments and their standardization

Metrological properties of measuring instruments- these are properties that have a direct impact on the results of measurements carried out by these means and on the error of these measurements.

Quantitative metrological properties are characterized by indicators of metrological properties, which are their metrological characteristics.

Metrological characteristics approved by ND are standardized metrological characteristics Metrological properties of measuring instruments are divided into:

1) properties that establish the scope of the measuring instruments:

2) properties that determine the precision and correctness of the obtained measurement results.

The properties that establish the scope of application of measuring instruments are determined by the following metrological characteristics:

1) measuring range;

2) threshold of sensitivity.

Measuring range- this is the range of values of the quantity in which the limiting values of errors are normalized. The lower and upper (right and left) limits of measurements are called the lower and upper limits of measurements.

Sensitivity threshold- this is the minimum value of the measured value that can cause a noticeable distortion of the received signal.

The properties that determine the precision and correctness of the obtained measurement results are determined by the following metrological characteristics:

1) the correctness of the results;

2) precision of results.

The accuracy of the results obtained by certain measuring instruments is determined by their error.

Error of measuring instruments- this is the difference between the result of measuring a quantity and the real (actual) value of this quantity. For a working measuring instrument, the real (valid) value of the measured quantity is the indication of the working standard of a lower level. Thus, the basis of comparison is the value shown by the measuring instrument, which is higher in the verification scheme than the tested measuring instrument.

Q n \u003d Q n? Q 0,

where AQ n is the error of the tested measuring instrument;

Q n - the value of a certain quantity obtained using the tested measuring instrument;

Rationing of metrological characteristics- this is the regulation of the limits of deviations of the values of the real metrological characteristics of measuring instruments from their nominal values. The main goal of standardization of metrological characteristics is to ensure their interchangeability and uniformity of measurements. The values of real metrological characteristics are established during the production of measuring instruments, in the future, during the operation of measuring instruments, these values must be checked. In the event that one or more of the normalized metrological characteristics goes beyond the regulated limits, the measuring instrument must either be immediately adjusted or withdrawn from service.

The values of metrological characteristics are regulated by the relevant standards of measuring instruments. Moreover, the metrological characteristics are normalized separately for normal and operating conditions for the use of measuring instruments. Normal conditions of use are conditions in which changes in metrological characteristics due to the influence of external factors (external magnetic fields, humidity, temperature) can be neglected. Operating conditions are conditions in which the change in influencing quantities has a wider range.

12. Metrological assurance, its basics

Metrological support, or MO for short, is the establishment and use of scientific and organizational foundations, as well as a number of technical means, norms and rules necessary to comply with the principle of unity and the required accuracy of measurements. To date, the development of MO is moving in the direction of transition from the existing narrow task of ensuring the unity and required accuracy of measurements to the new task of ensuring the quality of measurements. However, this term is also applicable in the form of the concept of "metrological support of the technological process (production, organization)", which implies MO measurements (tests or control) in this process, production, organization. The object of MO can be considered all stages of the life cycle (LC) of a product (product) or service, where the life cycle is perceived as a certain set of sequential interrelated processes of creating and changing the state of a product from the formulation of initial requirements for it to the end of operation or consumption. Often, at the stage of product development, in order to achieve a high quality product, the choice of controlled parameters, accuracy standards, tolerances, measuring instruments, control and testing is made. And in the process of developing MO, it is desirable to use a systematic approach, in which the specified support is considered as a certain set of interrelated processes united by one goal. This goal is to achieve the required measurement quality. In the scientific literature, as a rule, a number of such processes are distinguished:

1) establishing the range of measured parameters, as well as the most appropriate accuracy standards for product quality control and process control;

2) feasibility study and selection of measuring instruments, tests and control and establishment of their rational nomenclature;

3) standardization, unification and aggregation of the used control and measuring equipment;

4) development, implementation and certification of modern methods for performing measurement, testing and control (MVI);

5) verification, metrological certification and calibration of KIO or instrumentation, as well as test equipment used at the enterprise;

6) control over the production, condition, use and repair of KIO, as well as over the strict adherence to the rules of metrology and standards at the enterprise;

7) participation in the process of creating and implementing enterprise standards;

8) introduction of international, state, industry standards, as well as other regulatory documents of the State Standard;

9) carrying out metrological examination of projects of design, technological and regulatory documentation;

10) analysis of the state of measurements, development on its basis and implementation of various measures to improve the MO;

11) training of employees of relevant services and divisions of the enterprise to perform control and measuring operations.

The organization and holding of all events of the Moscow Region is the prerogative of the metrological services. Metrological support is based on four layers. Actually, they bear a similar name in the scientific literature - the foundations. So, these are the scientific, organizational, regulatory and technical foundations. I would like to pay special attention to the organizational foundations of metrological support. The organizational services of metrological support include the State Metrological Service and the Departmental Metrological Service.

The State Metrological Service, or GMS for short, is responsible for providing metrological measurements in Russia at the intersectoral level, and also carries out control and supervisory activities in the field of metrology. The HMS includes:

1) state scientific metrological centers (SSMC), metrological research institutes responsible according to the legislative framework for the application, storage and creation of state standards and the development of regulations on maintaining the uniformity of measurements in a fixed form of measurements;

2) bodies of the State Migration Service on the territory of the republics that are part of the Russian Federation, bodies of autonomous regions, bodies of autonomous districts, regions, territories, cities of Moscow and St. Petersburg.

The main activity of the HMS bodies is aimed at ensuring the uniformity of measurements in the country. It includes the creation of state and secondary standards, the development of systems for transferring the sizes of PV units to working measuring instruments, state supervision over the condition, use, production, and repair of measuring instruments, metrological examination of documentation and the most important types of products, and methodological guidance for MS of legal entities. The HMS is managed by Gosstandart.

A departmental metrological service, which, in accordance with the provisions of the Law “On Ensuring the Uniformity of Measurements”, can be created at an enterprise to ensure MO. It should be headed by a representative of the administration with appropriate knowledge and authority. is mandatory. Such areas of activity include:

1) health care, veterinary medicine, environmental protection, maintenance of labor safety;

2) trading operations and mutual settlements between sellers and buyers, which include, as a rule, transactions using slot machines and other devices;

3) state accounting operations;

4) defense of the state;

5) geodetic and hydrometeorological works;

6) banking, customs, tax and postal operations;

7) production of products supplied under contracts for the needs of the state in accordance with the legislative framework of the Russian Federation;

8) control and testing of product quality to ensure compliance with the mandatory requirements of state standards of the Russian Federation;

9) certification of goods and services without fail;

10) measurements carried out on behalf of a number of government agencies: courts, arbitration, prosecutors, government bodies of the Russian Federation;

11) registration activities related to national or international records in the field of sports. The metrological service of the state governing body includes the following components:

1) structural subdivisions of the chief metrologist as part of the central office of the state body;

2) head and base organizations of metrological services in industries and sub-sectors, appointed by the governing body;

3) metrological service of enterprises, associations, organizations and institutions.

Another important section of IR is its scientific and methodological foundations. So, the main component of these foundations are the State Scientific Metrological Centers (SSMC), which are created from the enterprises and organizations or their structural subdivisions under the jurisdiction of the State Standard, performing various operations on the creation, storage, improvement, application and storage of state standards of units of quantities, and , in addition, developing normative rules for the purpose of ensuring the uniformity of measurements, having in its composition highly qualified personnel. The assignment of the status of the SSMC to any enterprise, as a rule, does not affect the form of its ownership and organizational and legal forms, but only means that they are included in the group of objects that have special forms of state support. The main functions of the SSMC are as follows:

1) creation, improvement, application and storage of state standards of units of quantities;

2) carrying out applied and fundamental research and development in the field of metrology, which can include the creation of various experimental installations, initial measures and scales to ensure the uniformity of measurements;

3) transfer from state standards of initial data on the size of units of quantities;

4) carrying out state tests of measuring instruments;

5) development of equipment required for HMS;

6) development and improvement of regulatory, organizational, economic and scientific foundations of activities aimed at ensuring the uniformity of measurements depending on specialization;

7) interaction with the metrological service of federal executive authorities, organizations and enterprises that have the status of a legal entity;

8) providing information about the uniformity of measurements of enterprises and organizations

9) organization of various events related to the activities of the GSVCH, GSSSD and GSSO;

10) conducting an examination of sections of the Ministry of Defense of federal and other programs;

11) organization of metrological examination and measurements at the request of a number of state bodies: court, arbitration, prosecutor's office or federal executive bodies;

12) training and retraining of highly qualified personnel;

13) participation in the comparison of state standards with national standards, available in a number of foreign countries, as well as participation in the development of international norms and rules.

The activities of the GNMC are regulated by Decree of the Government of the Russian Federation of February 12, 1994 No. 100.

An important component of the basis of the MO are, as mentioned above, methodological instructions and guidance documents, which mean regulatory documents of methodological content, are developed by organizations subordinate to the State Standard of the Russian Federation. So, in the field of scientific and methodological foundations of metrological support, the State Standard of Russia organizes:

1) carrying out research activities and development work in assigned areas of activity, and also establishes the rules for carrying out work on metrology, standardization, accreditation and certification, as well as state control and supervision in subordinate areas, provides methodological guidance for these works;

2) provides methodological guidance for training in the areas of metrology, certification and standardization, establishes requirements for the degree of qualification and competence of personnel. Organizes training, retraining and advanced training of specialists.

13. Measurement error

In the practice of using measurements, their accuracy becomes a very important indicator, which is the degree of closeness of the measurement results to some actual value, which is used for a qualitative comparison of measuring operations. And as a quantitative assessment, as a rule, the measurement error is used. Moreover, the smaller the error, the higher the accuracy is considered.

According to the law of the theory of errors, if it is necessary to increase the accuracy of the result (with the excluded systematic error) by 2 times, then the number of measurements must be increased by 4 times; if it is required to increase the accuracy by 3 times, then the number of measurements is increased by 9 times, etc.

The process of assessing the measurement error is considered one of the most important activities in ensuring the uniformity of measurements. Naturally, there are a huge number of factors that affect the measurement accuracy. Consequently, any classification of measurement errors is rather conditional, since often, depending on the conditions of the measurement process, errors can appear in different groups. In this case, according to the principle of dependence on the form, these expressions of the measurement error can be: absolute, relative and reduced.

In addition, on the basis of dependence on the nature of the manifestation, the causes of occurrence and the possibilities for eliminating measurement errors, they can be components. In this case, the following error components are distinguished: systematic and random.

The systematic component remains constant or changes with subsequent measurements of the same parameter.

The random component changes with repeated changes in the same parameter randomly. Both components of the measurement error (both random and systematic) appear simultaneously. Moreover, the value of the random error is not known in advance, since it may arise due to a number of unspecified factors. This type of error cannot be completely excluded, but their influence can be somewhat reduced by processing the measurement results.

The systematic error, and this is its peculiarity, when compared with a random error, which is detected regardless of its sources, is considered by components in connection with the sources of occurrence.

Components of the error can also be divided into: methodological, instrumental and subjective. Subjective systematic errors are associated with the individual characteristics of the operator. Such an error may occur due to errors in the reading of readings or the inexperience of the operator. Basically, systematic errors arise due to the methodological and instrumental components. The methodological component of the error is determined by the imperfection of the measurement method, the methods of using the SI, the incorrectness of the calculation formulas and the rounding of the results. The instrumental component appears due to the inherent error of the MI, determined by the accuracy class, the influence of the MI on the result, and the resolution of the MI. There is also such a thing as "gross errors or misses", which may appear due to erroneous actions of the operator, malfunction of the measuring instrument, or unforeseen changes in the measurement situation. Such errors, as a rule, are detected in the process of reviewing the measurement results using special criteria. An important element of this classification is the error prevention, understood as the most rational way to reduce the error, is to eliminate the influence of any factor.

14. Types of errors

There are the following types of errors:

1) absolute error;

2) relative error;

3) reduced error;

4) basic error;

5) additional error;

6) systematic error;

7) random error;

8) instrumental error;

9) methodological error;

10) personal error;

11) static error;

12) dynamic error.

Measurement errors are classified according to the following criteria.

According to the method of mathematical expression, the errors are divided into absolute errors and relative errors.

According to the interaction of changes in time and the input value, the errors are divided into static errors and dynamic errors.

According to the nature of the appearance of errors, they are divided into systematic errors and random errors.

Absolute error is the value calculated as the difference between the value of the quantity obtained during the measurement process and the real (actual) value of the given quantity.

The absolute error is calculated using the following formula:

Q n \u003d Q n? Q 0,

where AQ n is the absolute error;

Q n- the value of a certain quantity obtained in the process of measurement;

Q 0 - the value of the same quantity, taken as the base of comparison (real value).

Absolute error of measure is the value calculated as the difference between the number, which is the nominal value of the measure, and the real (actual) value of the quantity reproduced by the measure.

Relative error is a number that reflects the degree of accuracy of the measurement.

The relative error is calculated using the following formula:

where?Q is the absolute error;

Q 0 is the real (actual) value of the measured quantity.

Reduced error is the value calculated as the ratio of the absolute error value to the normalizing value.

The normalizing value is defined as follows:

1) for measuring instruments for which a nominal value is approved, this nominal value is taken as a normalizing value;

2) for measuring instruments, in which the zero value is located on the edge of the measurement scale or outside the scale, the normalizing value is taken equal to the final value from the measurement range. The exception is measuring instruments with a significantly uneven measurement scale;

3) for measuring instruments, in which the zero mark is located inside the measurement range, the normalizing value is taken equal to the sum of the final numerical values of the measurement range;

4) for measuring instruments (measuring instruments), in which the scale is uneven, the normalizing value is taken equal to the entire length of the measurement scale or the length of that part of it that corresponds to the measurement range. The absolute error is then expressed in units of length.

Measurement error includes instrumental error, methodological error and reading error. Moreover, the reading error arises due to the inaccuracy in determining the division fractions of the measurement scale.

Instrumental error- this is the error arising due to the errors made in the manufacturing process of the functional parts of the error measuring instruments.

Methodological error is an error due to the following reasons:

1) inaccuracy in building a model of the physical process on which the measuring instrument is based;

2) incorrect use of measuring instruments.

Subjective error- this is an error arising due to the low degree of qualification of the operator of the measuring instrument, as well as due to the error of the human visual organs, i.e. the human factor is the cause of the subjective error.

Errors in the interaction of changes in time and the input value are divided into static and dynamic errors.

Static error- this is the error that occurs in the process of measuring a constant (not changing in time) value.

Dynamic error- this is an error, the numerical value of which is calculated as the difference between the error that occurs when measuring a non-constant (variable in time) quantity, and a static error (the error in the value of the measured quantity at a certain point in time).

According to the nature of the dependence of the error on the influencing quantities, the errors are divided into basic and additional.

Basic error is the error obtained under normal operating conditions of the measuring instrument (at normal values of the influencing quantities).

Additional error is the error that occurs when the values of the influencing quantities do not correspond to their normal values, or if the influencing quantity goes beyond the boundaries of the area of normal values.

Normal conditions are the conditions under which all values of the influencing quantities are normal or do not go beyond the boundaries of the range of normal values.

Working conditions- these are conditions in which the change in the influencing quantities has a wider range (the values of the influencing ones do not go beyond the boundaries of the working range of values).

Working range of values of the influencing quantity is the range of values in which the values of the additional error are normalized.

According to the nature of the dependence of the error on the input value, the errors are divided into additive and multiplicative.

Additive error- this is the error that occurs due to the summation of numerical values and does not depend on the value of the measured quantity, taken modulo (absolute).

Multiplicative error- this is an error that changes along with a change in the values of the quantity being measured.

It should be noted that the value of the absolute additive error is not related to the value of the measured quantity and the sensitivity of the measuring instrument. Absolute additive errors are unchanged over the entire measurement range.

The value of the absolute additive error determines the minimum value of the quantity that can be measured by the measuring instrument.

The values of multiplicative errors change in proportion to changes in the values of the measured quantity. The values of multiplicative errors are also proportional to the sensitivity of the measuring instrument. The multiplicative error arises due to the influence of influencing quantities on the parametric characteristics of the instrument elements.

Errors that may occur during the measurement process are classified according to the nature of their occurrence. Allocate:

1) systematic errors;

2) random errors.

Gross errors and misses may also appear in the measurement process.

Systematic error- this is an integral part of the entire error of the measurement result, which does not change or changes naturally with repeated measurements of the same value. Usually, a systematic error is tried to be eliminated by possible means (for example, by using measurement methods that reduce the likelihood of its occurrence), but if a systematic error cannot be excluded, then it is calculated before the start of measurements and appropriate corrections are made to the measurement result. In the process of normalizing the systematic error, the boundaries of its admissible values are determined. The systematic error determines the correctness of measurements of measuring instruments (metrological property).

Systematic errors in some cases can be determined experimentally. The measurement result can then be refined by introducing a correction.

Methods for eliminating systematic errors are divided into four types:

1) elimination of causes and sources of errors before the start of measurements;

2) elimination of errors in the process of already begun measurement by methods of substitution, compensation of errors in sign, oppositions, symmetrical observations;

3) correction of the measurement results by making an amendment (elimination of the error by calculations);

4) determination of the limits of systematic error in case it cannot be eliminated.

Elimination of the causes and sources of errors before the start of measurements. This method is the best option, since its use simplifies the further course of measurements (there is no need to eliminate errors in the process of an already started measurement or to amend the result).

To eliminate systematic errors in the process of an already started measurement, various methods are used.

Amendment method is based on knowledge of the systematic error and the current patterns of its change. When using this method, the measurement result obtained with systematic errors is subject to corrections equal in magnitude to these errors, but opposite in sign.

substitution method consists in the fact that the measured value is replaced by a measure placed in the same conditions in which the object of measurement was located. The substitution method is used when measuring the following electrical parameters: resistance, capacitance and inductance.

Sign error compensation method consists in the fact that the measurements are performed twice in such a way that the error, unknown in magnitude, is included in the measurement results with the opposite sign.

Contrasting method similar to sign-based compensation. This method consists in that the measurements are performed twice in such a way that the source of the error in the first measurement has the opposite effect on the result of the second measurement.

random error- this is a component of the error of the measurement result, which changes randomly, irregularly during repeated measurements of the same value. The occurrence of a random error cannot be foreseen and predicted. Random error cannot be completely eliminated; it always distorts the final measurement results to some extent. But you can make the measurement result more accurate by taking repeated measurements. The cause of a random error can be, for example, a random change in external factors affecting the measurement process. A random error during multiple measurements with a sufficiently high degree of accuracy leads to scattering of the results.

Misses and blunders are errors that are much larger than the systematic and random errors expected under the given measurement conditions. Slips and gross errors may appear due to gross errors in the measurement process, a technical malfunction of the measuring instrument, and unexpected changes in external conditions.

15. Quality of measuring instruments

Meter quality- this is the level of compliance of the device with its intended purpose. Therefore, the quality of a measuring instrument is determined by the extent to which, when using a measuring instrument, the purpose of the measurement is achieved.

The main purpose of the measurement is the receipt of reliable and accurate information about the object of measurement.

In order to determine the quality of the device, it is necessary to consider the following characteristics:

1) device constant;

2) sensitivity of the device;

3) sensitivity threshold of the measuring device;

4) the accuracy of the measuring device.

Instrument constant- this is a certain number multiplied by the reading in order to obtain the desired value of the measured value, i.e., the reading of the device. The constant of the device in some cases is set as the value of the division of the scale, which is the value of the measured quantity corresponding to one division.

Instrument sensitivity- this is a number in the numerator of which is the value of the linear or angular movement of the pointer (if we are talking about a digital measuring device, then the numerator will be a change in the numerical value, and the denominator will be the change in the measured value that caused this movement (or change in the numerical value)) .

Sensitivity threshold of the measuring instrument- a number that is the minimum value of the measured value that the device can fix.

Meter accuracy- this is a characteristic expressing the degree of compliance of the measurement results with the present value of the measured quantity. The accuracy of a measuring instrument is determined by setting lower and upper limits for the maximum possible error.

The division of devices into accuracy classes based on the value of the permissible error is practiced.

Accuracy class of measuring instruments- this is a generalizing characteristic of measuring instruments, which is determined by the boundaries of the main and additional permissible errors and other characteristics that determine accuracy. Accuracy classes of a certain type of measuring instruments are approved in the regulatory documentation. Moreover, for each individual accuracy class, certain requirements for metrological characteristics are approved. The combination of established metrological characteristics determines the degree of accuracy of a measuring instrument belonging to a given accuracy class.

The accuracy class of the measuring instrument is determined in the course of its development. Since the metrological characteristics usually deteriorate during operation, it is possible, based on the results of the calibration (verification) of the measuring instrument, to lower its accuracy class.

16. Errors of measuring instruments

The errors of measuring instruments are classified according to the following criteria:

1) according to the way of expression;

2) by the nature of the manifestation;

3) in relation to the conditions of use. According to the method of expression, absolute and relative errors are distinguished.

The absolute error is calculated by the formula:

?Q n \u003d Q n ?Q 0,

where ? Q n is the absolute error of the tested measuring instrument;

Q n- the value of a certain quantity obtained using the tested measuring instrument;

Q 0 - the value of the same quantity, taken as the base of comparison (real value).

Relative error is a number that reflects the degree of accuracy of a measuring instrument. The relative error is calculated using the following formula:

where ? Q is the absolute error;

Q 0 - the real (real) value of the measured value.

Relative error is expressed as a percentage.

According to the nature of the manifestation of errors, they are divided into random and systematic.

In relation to the conditions of application, the errors are divided into basic and additional.

Basic error of measuring instruments- this is the error, which is determined if the measuring instruments are used under normal conditions.

Additional error of measuring instruments- this is an integral part of the error of the measuring instrument, which occurs additionally if any of the influencing quantities goes beyond its normal value.

17. Metrological support of measuring systems

Metrological support- this is the approval and use of scientific, technical and organizational foundations, technical instruments, norms and standards in order to ensure the unity and established accuracy of measurements. Metrological support in its scientific aspect is based on metrology.

The following goals of metrological support can be distinguished:

1) achieving higher product quality;

2) ensuring the greatest efficiency of the accounting system;

3) provision of preventive measures, diagnostics and treatment;

4) ensuring effective production management;

5) ensuring a high level of efficiency of scientific work and experiments;

6) ensuring a higher degree of automation in the field of transport management;

7) ensuring the effective functioning of the system of regulation and control of working and living conditions;

8) improving the quality of environmental supervision;

9) improving the quality and increasing the reliability of communications;

10) ensuring an effective system for evaluating various natural resources.

Metrological support of technical devices- this is

a set of scientific and technical means, organizational measures and activities carried out by the relevant institutions in order to achieve unity and the required accuracy of measurements, as well as the established characteristics of technical instruments.

Measuring system- a measuring instrument, which is a combination of measures, IP, measuring instruments, etc., performing similar functions, located in different parts of a certain space and designed to measure a certain number of physical quantities in this space.

Measuring systems are used for:

1) the technical characteristics of the measurement object, obtained by carrying out measurement transformations of a certain number of quantities dynamically changing in time and distributed in space;

2) automated processing of the obtained measurement results;

3) fixing the obtained measurement results and the results of their automated processing;

4) transfer of data to the output signals of the system. Metrological support of measuring systems implies:

1) definition and standardization of metrological characteristics for measuring channels;

2) verification of technical documentation for compliance with metrological characteristics;

3) carrying out tests of measuring systems to determine the type to which they belong;

4) carrying out tests to determine the conformity of the measuring system to the established type;

5) certification of measuring systems;

6) carrying out calibration (checking) of measuring systems;

7) ensuring metrological control over the production and use of measuring systems.

Measuring channel of the measuring system- this is a part of the measuring system, technically or functionally isolated, designed to perform a certain final function (for example, to perceive the measured value or to obtain a number or code that is the result of measurements of this value). Share:

1) simple measuring channels;

2) complex measuring channels.

Simple measuring channel is a channel that uses a direct method of measurement, implemented through ordered measurement transformations.

In a complex measuring channel, a primary part and a secondary part are distinguished. In the primary part, a complex measuring channel is a combination of a certain number of simple measuring channels. Signals from the output of simple measuring channels of the primary part are used for indirect, cumulative or joint measurements or to obtain a signal proportional to the measurement result in the secondary part.

Measuring component of the measuring system- this is a measuring instrument with separately normalized metrological characteristics. An example of a measuring component of a measuring system is a measuring device. The measurement components of the measurement system also include analog computing devices (devices that perform measurement conversions). Analog computing devices belong to the group of devices with one or more inputs.

Measuring components of measuring systems are of the following types.

Connecting component is a technical device or element of the environment used to exchange signals containing information about the measured value between the components of the measuring system with the least possible distortion. An example of a connecting component is a telephone line, a high-voltage power line, transitional devices.

Compute Component is a digital device (part of a digital device) designed to perform calculations, with installed software. The compute component is used to compute

merging the results of measurements (direct, indirect, joint, cumulative), which are a number or a corresponding code, the calculations are made on the basis of the results of primary transformations in the measuring system. The computing component also performs logical operations and coordination of the measuring system.

Complex component is an integral part of the measuring system, which is a technically or territorially unified set of components. The complex component completes the measuring transformations, as well as computational and logical operations that are approved in the accepted algorithm for processing measurement results for other purposes.

Auxiliary Component is a technical device designed to ensure the normal functioning of the measuring system, but does not take part in the process of measuring transformations.

According to the relevant GOSTs, the metrological characteristics of the measuring system must be standardized for each measuring channel included in the measuring system, as well as for the complex and measuring components of the measuring system.

As a rule, the manufacturer of the measuring system determines the general standards for the metrological characteristics of the measuring channels of the measuring system.

The normalized metrological characteristics of the measuring channels of the measuring system are designed to:

1) ensure the determination of the measurement error using measuring channels under operating conditions;

2) to ensure effective control over the compliance of the measuring channel of the measuring system with the normalized metrological characteristics during the testing of the measuring system. If the determination or control over the metrological characteristics of the measuring channel of the measuring system cannot be carried out experimentally for the entire measuring channel, the normalization of the metrological characteristics is carried out for the constituent parts of the measuring channel. Moreover, the combination of these parts should be a whole measuring channel

It is possible to normalize the error characteristics as the metrological characteristics of the measuring channel of the measuring system both under normal conditions of use of the measuring components and under operating conditions, which are characterized by such a combination of influencing factors, in which the modulus of the numerical value of the measurement channel error characteristics has the maximum possible value. For greater efficiency, for intermediate combinations of influencing factors, the measurement channel error characteristics are also normalized. These characteristics of the error of the measuring channels of the measuring system must be checked by calculating them according to the metrological characteristics of the components of the measuring system, which constitute the measuring channel as a whole. Moreover, the calculated values of the error characteristics of the measuring channels may not be verified experimentally. But nevertheless, it is mandatory to carry out control of metrological characteristics for all constituent parts (components) of the measuring system, the norms of which are the initial data in the calculation.

The normalized metrological characteristics of complex components and measuring components should:

1) ensure the determination of the error characteristics of the measuring channels of the measuring system under operating conditions of use using the normalized metrological characteristics of the components;

2) ensure that these components are effectively controlled during type testing and verification of compliance with specified metrological characteristics. For the computing components of the measuring system, if their software was not taken into account in the process of normalizing the metrological characteristics, the calculation errors are normalized, the source of which is the functioning of the software (calculation algorithm, its software implementation). For the computing components of the measuring system, other characteristics can also be normalized, provided that the specifics of the computing component are taken into account, which can affect the characteristics of the constituent parts of the measurement channel error (characteristics of the error component), if the component error arises due to the use of this program for processing the measurement results.

The technical documentation for the operation of the measuring system must include a description of the algorithm and a program that operates in accordance with the described algorithm. This description should allow calculating the error characteristics of the measurement results using the error characteristics of the measuring channel component of the measuring system located in front of the computing component.

For connecting components of the measuring system, two types of characteristics are normalized:

1) characteristics that provide such a value of the error component of the measuring channel caused by the connecting component, which can be neglected;

2) characteristics that allow determining the value of the error component of the measuring channel caused by the connecting component.

18. Choice of measuring instruments

When choosing measuring instruments, first of all, the permissible error value for a given measurement, established in the relevant regulatory documents, should be taken into account.

If the permissible error is not provided for in the relevant regulatory documents, the maximum permissible measurement error should be regulated in the technical documentation for the product.

The choice of measuring instruments should also take into account:

1) tolerances;

2) measurement methods and control methods. The main criterion for choosing measuring instruments is the compliance of measuring instruments with the requirements of measurement reliability, obtaining real (real) values of measured quantities with a given accuracy at minimal time and material costs.

For the optimal choice of measuring instruments, it is necessary to have the following initial data:

1) the nominal value of the measured quantity;

2) the value of the difference between the maximum and minimum value of the measured value, regulated in the regulatory documentation;

3) information about the conditions for carrying out measurements.

If it is necessary to choose a measuring system, guided by the criterion of accuracy, then its error should be calculated as the sum of the errors of all elements of the system (measures, measuring instruments, measuring transducers), in accordance with the law established for each system.

The preliminary selection of measuring instruments is made in accordance with the criterion of accuracy, and the final choice of measuring instruments should take into account the following requirements:

1) to the working area of values of quantities that affect the measurement process;

2) to the dimensions of the measuring instrument;

3) to the mass of the measuring instrument;

4) to the design of the measuring instrument.

When choosing measuring instruments, it is necessary to take into account the preference for standardized measuring instruments.

19. Methods for determining and accounting for errors

Methods for determining and accounting for measurement errors are used to:

1) based on the measurement results, obtain the real (real) value of the measured quantity;

2) determine the accuracy of the results, i.e., the degree of their compliance with the real (real) value.

In the process of determining and accounting for errors, the following are evaluated:

1) mathematical expectation;

2) standard deviation.

Point Parameter Estimation(mathematical expectation or standard deviation) is an estimate of a parameter that can be expressed as a single number. A point estimate is a function of the experimental data and, therefore, must itself be a random variable distributed according to a law that depends on the distribution law for the values of the initial random variable. The distribution law for the values of a point estimate will also depend on the estimated parameter and on the number of trials (experiments).

Point estimates are of the following types:

1) unbiased point estimate;

2) effective point estimate;

3) consistent point estimate.

Unbiased point estimate is an estimate of the error parameter, the mathematical expectation of which is equal to this parameter.

Efficient Point Estimation is a point estimate. whose variance is less than the variance of any other estimate of this parameter.

Consistent point estimate- this is an estimate that, with an increase in the number of tests, tends to the value of the parameter being evaluated.

The main methods for determining grades:

1) maximum likelihood method (Fisher method);

2) the method of least squares.

1. Maximum likelihood method is based on the idea that information about the actual value of the measured quantity and the dispersion of measurement results, obtained by multiple observations, is contained in a series of observations.

The maximum likelihood method consists in finding estimates for which the likelihood function passes through its maximum.

Maximum Likelihood Estimates are estimates of the standard deviation and estimates of the true value.

If random errors are distributed according to a normal distribution, then the maximum likelihood estimate for the true value is the arithmetic mean of the observations, and the variance estimate is the arithmetic mean of the squared deviations of the values from the mathematical expectation.

The advantage of maximum likelihood estimates is that these estimates:

1) asymptotically unbiased;

2) asymptotically efficient;

3) are asymptotically distributed according to the normal law.

2. Least square method consists in the fact that from a certain class of estimates, the estimate with the minimum variance (the most effective) is taken. Of all linear estimates of the real value, where some constants are present, only the arithmetic mean reduces to the smallest value of the variance. In this regard, under the condition of the distribution of random error values according to the normal distribution law, the estimates obtained using the least squares method are identical to the maximum likelihood estimates. Estimation of parameters using intervals is carried out by finding confidence intervals within which the real values of the estimated parameters are located with given probabilities.

Confidence limit of random deviation is a number representing the length of the confidence interval divided by two.

With a sufficiently large number of trials, the confidence interval decreases significantly. If the number of trials increases, then it is permissible to increase the number of confidence intervals.

Gross error detection

gross errors are errors that are much larger than the systematic and random errors expected under the given measurement conditions. Slips and gross errors may appear due to gross errors in the measurement process, a technical malfunction of the measuring instrument, and unexpected changes in external conditions. In order to exclude gross errors, it is recommended to approximately determine the value of the measured quantity before the start of measurements.

If, during measurements, it turns out that the result of an individual observation is very different from other results obtained, it is necessary to establish the reasons for such a difference. Results obtained with a sharp difference can be discarded and this value re-measured. However, in some cases, discarding such results can cause a noticeable distortion of the scatter of a number of measurements. In this regard, it is recommended not to discard thoughtlessly different results, but to supplement them with the results of repeated measurements.

If it is necessary to exclude gross errors in the process of processing the results obtained, when it is no longer possible to correct the conditions for the measurements and carry out repeated measurements, then statistical methods are used.

The general method for testing statistical hypotheses makes it possible to find out whether there is a gross error in a given measurement result.

20. Processing and presentation of measurement results

Usually measurements are single. Under normal conditions, their accuracy is quite sufficient.

The result of a single measurement is presented in the following form:

where Y i- the value of the i -th indication;

I - correction.

The error of the result of a single measurement is determined when the measurement method is approved.

In the process of processing measurement results, various types of distribution law (normal distribution law, uniform distribution law, correlation distribution law) of the measured value are used (in this case, it is considered as random).

Processing the results of direct equal measurements Direct measurements- these are measurements by which the value of the measured quantity is directly obtained. Equivalent or equally scattered are direct, mutually independent measurements of a certain quantity, and the results of these measurements can be considered as random and distributed according to one distribution law.

Usually, when processing the results of direct, equally accurate measurements, it is assumed that the results and measurement errors are distributed according to the normal distribution law.

After removing the calculations, the value of the mathematical expectation is calculated by the formula:

where x i is the value of the measured quantity;

n is the number of measurements taken.

Then, if the systematic error is determined, its value is subtracted from the calculated value of the mathematical expectation.

Then the value of the standard deviation of the values of the measured value from the mathematical expectation is calculated.

Algorithm for processing the results of multiple equally accurate measurements

If the systematic error is known, then it must be excluded from the measurement results.

Calculate the mathematical expectation of the measurement results. As a mathematical expectation, the arithmetic mean of the values is usually taken.

Set the value of the random error (deviation from the arithmetic mean) of the result of a single measurement.

Calculate the variance of the random error. Calculate the standard deviation of the measurement result.

Check the assumption that the measurement results are distributed according to the normal law.

Find the value of the confidence interval and confidence error.

Determine the value of the entropy error and the entropy coefficient.

21. Verification and calibration of measuring instruments

Calibration of measuring instruments is a set of actions and operations that determine and confirm the real (actual) values of metrological characteristics and (or) the suitability of measuring instruments that are not subject to state metrological control.

The suitability of a measuring instrument is a characteristic determined by the compliance of the metrological characteristics of the measuring instrument with the approved (in regulatory documents or by the customer) technical requirements. The calibration laboratory determines the suitability of the measuring instrument.

Calibration replaced the verification and metrological certification of measuring instruments, which were carried out only by the bodies of the state metrological service. Calibration, unlike verification and metrological certification of measuring instruments, can be carried out by any metrological service, provided that it has the ability to provide appropriate conditions for calibration. Calibration is carried out on a voluntary basis and can even be carried out by the metrological service of the enterprise.

Nevertheless, the metrological service of the enterprise is obliged to fulfill certain requirements. The main requirement for the metrological service is to ensure that the working measuring instrument complies with the state standard, that is, calibration is part of the national system for ensuring the uniformity of measurements.

There are four methods of verification (calibration) of measuring instruments:

1) method of direct comparison with the standard;

2) method of comparison using a computer;

3) method of direct measurements of the quantity;

4) method of indirect measurements of quantity.

Method of direct comparison with the standard funds

measurements subjected to calibration, with the corresponding standard of a certain category, is practiced for various measuring instruments in such areas as electrical measurements, magnetic measurements, determination of voltage, frequency and current strength. This method is based on the implementation of measurements of the same physical quantity by a calibrated (verified) instrument and a reference instrument simultaneously. The error of the calibrated (verified) device is calculated as the difference between the readings of the calibrated device and the reference device (i.e., the readings of the reference device are taken as the real value of the measured physical quantity).

Advantages of the method of direct comparison with the standard:

1) simplicity;

2) visibility;

3) the possibility of automatic calibration (verification);

4) the possibility of calibration using a limited number of instruments and equipment.

Comparison method using a computer is carried out using a comparator - a special device, through which the comparison of the readings of the calibrated (verified) measuring instrument and the readings of the reference measuring instrument is carried out. The need to use a comparator is due to the impossibility of directly comparing the readings of measuring instruments that measure the same physical quantity. A comparator can be a measuring instrument that equally perceives the signals of the reference measuring instrument and the instrument being calibrated (verified). The advantage of this method is the sequence in time of comparison of values.

Method of direct measurements of quantity used in cases where it is possible to compare the calibrated measuring instrument with the reference one within the established measurement limits. The direct measurement method is based on the same principle as the direct comparison method. The difference between these methods is that using the method of direct measurements, a comparison is made on all numerical marks of each range (subrange).

Method of indirect measurements is used in cases where the real (real) values of the measured physical quantities cannot be obtained through direct measurements or when indirect measurements are higher in accuracy than direct measurements. When using this method, to obtain the desired value, first they look for the values of the quantities associated with the desired value by a known functional dependence. And then, based on this dependence, the desired value is calculated by calculation. The method of indirect measurements, as a rule, is used in automated calibration (verification) installations.

In order to transfer the dimensions of units of measurement to working instruments from standards of units of measurement without large errors, verification schemes are compiled and applied.

Verification charts- this is a regulatory document that approves the subordination of measuring instruments that take part in the process of transferring the size of a unit of measurement of a physical quantity from a standard to working measuring instruments using certain methods and indicating an error. Verification schemes confirm the metrological subordination of the state standard, discharge standards and measuring instruments.

Verification schemes are divided into:

1) state verification schemes;

2) departmental verification schemes;

3) local verification schemes.

State verification schemes established and valid for all measuring instruments of a certain type used within the country.

Departmental verification schemes are established and act on measuring instruments of a given physical quantity subject to departmental verification. Departmental verification schemes should not conflict with state verification schemes if they are established for measuring instruments of the same physical quantities. Departmental verification schemes can be established in the absence of a state verification scheme. In departmental verification schemes, it is possible to directly indicate certain types of measuring instruments.

Local verification schemes are used by the metrological services of ministries and are also valid for measuring instruments of enterprises subordinate to them. A local verification scheme may apply to measuring instruments used at a particular enterprise. Local verification schemes must necessarily meet the subordination requirements approved by the state verification scheme. State verification schemes are drawn up by the research institutes of the State Standard of the Russian Federation. The research institutes of the State Standard are the owners of state standards.

Departmental verification schemes and local verification schemes are presented in the form of drawings.

State verification schemes are established by the State Standard of the Russian Federation, and local verification schemes are established by metrological services or heads of enterprises.

The verification scheme approves the procedure for transferring the size of units of measurement of one or more physical quantities from state standards to working measuring instruments. The verification scheme must contain at least two steps of transferring the size of units of measurement.

The drawings representing the verification scheme must contain:

1) names of measuring instruments;

2) names of verification methods;

3) nominal values of physical quantities;

4) ranges of nominal values of physical quantities;

5) permissible values of errors of measuring instruments;

6) permissible values of errors of verification methods.

22. Legal basis for metrological support. The main provisions of the Law of the Russian Federation "On ensuring the uniformity of measurements"

Unity of measurements- this is a characteristic of the measurement process, which means that the measurement results are expressed in units of measurement established and accepted by law and the measurement accuracy assessment has an appropriate confidence level.

The main principles of the unity of measurements:

1) determination of physical quantities with the obligatory use of state standards;

2) the use of legally approved measuring instruments subject to state control and with unit sizes transferred directly from state standards;

3) the use of only legally approved units of measurement of physical quantities;

4) ensuring mandatory systematic control over the characteristics of the operated measuring instruments at certain intervals;

5) ensuring the necessary guaranteed accuracy of measurements when using calibrated (verified) measuring instruments and established methods for performing measurements;

6) the use of the obtained measurement results under the obligatory condition of estimating the error of these results with a specified probability;

7) ensuring control over the compliance of measuring instruments with metrological rules and characteristics;

8) ensuring state and departmental supervision of measuring instruments.

The Law of the Russian Federation “On Ensuring the Uniformity of Measurements” was adopted in 1993. Prior to the adoption of this Law, the norms in the field of metrology were not regulated by law At the time of adoption, the Law contained many innovations, from approved terminology to the licensing of metrological activities in the country. duties of state metrological control and state metrological supervision, new calibration rules have been established, the concept of voluntary certification of measuring instruments has been introduced.

Basic provisions.

The primary aims of the law are:

1) protection of the legitimate rights and interests of citizens of the Russian Federation, the rule of law and the economy of the Russian Federation from possible negative consequences caused by unreliable and inaccurate measurement results;

2) assistance in the development of science, technology and economics by regulating the use of state standards of units of quantities and the application of measurement results with guaranteed accuracy. Measurement results should be expressed in national units of measurement;

3) promoting the development and strengthening of international and inter-company relations and ties;

4) regulation of requirements for the manufacture, production, use, repair, sale and import of measuring instruments produced by legal entities and individuals;

5) integration of the measurement system of the Russian Federation into world practice.

Areas of application of the Law: trade; healthcare; environmental Protection; economic and foreign economic activity; some areas of production related to the calibration (verification) of measuring instruments by metrological services belonging to legal entities, carried out using standards subordinate to state measurement standards.

The Law legislates the following basic concepts:

1) unity of measurements;

2) measuring instrument;

3) the standard of the unit of magnitude;

4) the state standard of the unit of magnitude;

5) regulatory documents to ensure the uniformity of measurements;

6) metrological service;

7) metrological control;

8) metrological supervision;

9) calibration of measuring instruments;

10) calibration certificate.

All definitions approved in the Law are based on the official terminology of the International Organization of Legal Metrology (OIML).

The main articles of the law regulate:

1) the structure of the organization of state management bodies to ensure the uniformity of measurements;

2) regulatory documents that ensure the uniformity of measurements;

3) established units of measurement of physical quantities and state standards of units of quantities;

4) measuring instruments;

5) measurement methods.

The law approves the State Metrological Service and other services involved in ensuring the uniformity of measurements, the metrological services of state governing bodies and the forms of implementation of state metrological control and supervision.

The Law defines the types of liability for violations of the Law.

The Law approves the composition and powers of the State Metrological Service.

In accordance with the Law, an institution for licensing metrological activities has been established in order to protect the legal rights of consumers. Only the bodies of the State Metrological Service have the right to issue a license.

New types of state metrological supervision have been established:

1) for the quantity of alienated goods;

2) for the quantity of goods in the package in the process of their packaging and sale.

In accordance with the provisions of the Law, the area of distribution of state metrological control is being increased. Banking operations, postal operations, tax operations, customs operations, and mandatory product certification were added to it.

In accordance with the Law, a system of certification of measuring instruments based on a voluntary principle is introduced, which checks measuring instruments for compliance with metrological rules and the requirements of the Russian system of calibration of measuring instruments.

23. Metrological service in Russia

The State Metrological Service of the Russian Federation (GMS) is an association of state metrological bodies and is engaged in coordinating activities to ensure the uniformity of measurements. There are the following metrological services:

1) State metrological service;

2) Public service of time and frequency and determining the parameters of the Earth's rotation;

3) State Service of Reference Materials for the Composition and Properties of Substances and Materials;

4) State Service for Standard Reference Data on Physical Constants and Properties of Substances and Materials;

5) metrological services of government bodies of the Russian Federation;

6) metrological services of legal entities. All the above services are managed by the State Committee of the Russian Federation for Standardization and Metrology (Gosstandart of Russia).

State metrological service contains:

1) state scientific metrological centers (SSMC);

2) bodies of the State Migration Service on the territory of the constituent entities of the Russian Federation. The State Metrological Service also includes centers of state standards, specializing in various units of measurement of physical quantities.

The State Service for Time and Frequency and the Determination of the Parameters of the Earth's Rotation (GSVCH) is engaged in ensuring the unity of measurements of time, frequency and determination of the parameters of the Earth's rotation at the interregional and intersectoral levels. The measuring information of the GSVCH is used by the navigation and control services for aircraft, ships and satellites, the Unified Energy System, etc.

The State Service of Reference Materials for the Composition and Properties of Substances and Materials (GSSO) is engaged in the creation and implementation of a system of reference materials for the composition and properties of substances and materials. The concept of materials includes:

1) metals and alloys;

2) petroleum products;

3) medicines, etc.

The GSSO is also developing instruments designed to compare the characteristics of reference materials and the characteristics of substances and materials produced by different types of enterprises (agricultural, industrial, etc.) in order to ensure control.

The State Service for Standard Reference Data on Physical Constants and Properties of Substances and Materials (GSSSD) develops accurate and reliable data on physical constants, properties of substances and materials (mineral raw materials, oil, gas, etc.). GSSSD measurement information is used by various organizations involved in the design of technical products with increased requirements for accuracy. GSSSD publishes reference data agreed with international metrological organizations.

Metrological services of state government bodies of the Russian Federation and metrological services of legal entities can be created in ministries, at enterprises, in institutions registered as a legal entity, in order to carry out various kinds of work to ensure the unity and proper accuracy of measurements, to ensure metrological control and supervision.

24. State system for ensuring the uniformity of measurements

The state system for ensuring the uniformity of measurements was created to ensure the uniformity of measurements within the country. The state system for ensuring the uniformity of measurements is implemented, coordinated and managed by the State Standard of the Russian Federation. Gosstandart of the Russian Federation is the state executive body in the field of metrology.

The system for ensuring the uniformity of measurements performs the following tasks:

1) ensures the protection of the rights and legally enshrined interests of citizens;

2) ensure the protection of the approved legal order;

3) ensure the protection of the economy.

The system for ensuring the uniformity of measurements performs these tasks by eliminating the negative consequences of unreliable and inaccurate measurements in all spheres of human life and society using constitutional norms, regulations and decrees of the government of the Russian Federation.

The system for ensuring the uniformity of measurements operates in accordance with:

1) the Constitution of the Russian Federation;

2) Law of the Russian Federation "On ensuring the uniformity of measurements";

3) Decree of the Government of the Russian Federation "On the organization of work on standardization, ensuring the uniformity of measurements, certification of products and services";

4) GOST R 8.000-2000 "State system for ensuring the uniformity of measurements".

The state system for ensuring the uniformity of measurements includes:

1) legal subsystem;

2) technical subsystem;

3) organizational subsystem.

The main tasks of the State System for Ensuring the Uniformity of Measurements are:

1) approval of effective ways to coordinate activities in the field of ensuring the uniformity of measurements;

2) ensuring research activities aimed at developing more accurate and advanced methods and methods for reproducing units of measurement of physical quantities and transferring their sizes from state standards to working measuring instruments;

3) approval of the system of units of measurement of physical quantities allowed for use;

4) establishment of measurement scales allowed for use;

5) approval of the fundamental concepts of metrology, regulation of the terms used;

6) approval of the system of state standards;

7) production and improvement of state standards;

8) approval of methods and rules for transferring the sizes of units of measurement of physical quantities from state standards to working measuring instruments;

9) carrying out calibration (verification) and certification of measuring instruments, which are not covered by the scope of state metrological control and supervision;

10) implementation of information coverage of the system for ensuring the uniformity of measurements;

11) improvement of the state system for ensuring the uniformity of measurements.

Legal subsystem- this is a set of interconnected acts (approved by law and by-law) that have the same goals and approve mutually agreed requirements for certain interconnected objects of the system for ensuring the uniformity of measurements.

Technical subsystem is the collection:

1) international standards;

2) state standards;

3) standards of units of measurement of physical quantities;

4) measurement scale standards;

5) standard samples of the composition and properties of substances and materials;

6) standard reference data on physical constants and properties of substances and materials;

7) measuring instruments and other instruments used for metrological control;

8) buildings and premises designed specifically for high-precision measurements;

9) research laboratories;

10) calibration laboratories.

The organizational subsystem includes metrological services.

25. State metrological control and supervision

State metrological control and supervision (GMKiN) is provided by the State Metrological Service to verify compliance with the norms of legal metrology, approved by the Law of the Russian Federation "On Ensuring the Uniformity of Measurements", state standards and other regulatory documents.

State metrological control and supervision applies to:

1) measuring instruments;

2) measurement standards;

3) measurement methods;

4) the quality of goods and other objects approved by legal metrology.

The scope of the State metrological control and supervision extends to:

1) healthcare;

2) veterinary practice;

3) environmental protection;

4) trade;

5) settlements between economic agents;

6) accounting operations carried out by the state;

7) the defense capability of the state;

8) geodetic works;

9) hydrometeorological works;

10) banking operations;

11) tax transactions;

12) customs operations;

13) postal operations;

14) products, the supply of which is carried out under state contracts;

15) verification and quality control of products for compliance with the mandatory requirements of state standards of the Russian Federation;

16) measurements that are carried out at the request of the judiciary, the prosecutor's office and other state bodies;

17) registration of national and international sports records.

It should be noted that the inaccuracy and unreliability of measurements in non-industrial areas such as healthcare can lead to serious consequences and a threat to safety. The inaccuracy and unreliability of measurements in the sphere of trade and banking operations, for example, can cause huge financial losses for both individuals and the state.

The objects of the State metrological control and supervision may be, for example, the following measuring instruments:

1) devices for measuring blood pressure;

2) medical thermometers;

3) devices for determining the level of radiation;

4) devices for determining the concentration of carbon monoxide in the exhaust gases of vehicles;

5) measuring instruments designed to control the quality of goods.

The Law of the Russian Federation establishes three types of state metrological control and three types of state metrological supervision.

Types of state metrological control:

1) determination of the type of measuring instruments;

2) verification of measuring instruments;

3) licensing of legal entities and individuals involved in the production and repair of measuring instruments. Types of state metrological supervision:

1) for the manufacture, condition and operation of measuring instruments, certified methods for performing measurements, standards of units of physical quantities, compliance with metrological rules and norms;

2) for the quantity of goods that are alienated in the course of trading operations;

3) for the quantity of goods packaged in packages of any kind, in the process of their packaging and sale.

Comparison devices metrology. State metrological service

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