Publications on instrumentation and control
Some Basics
Resolution, bit depth and readings
A characteristic of a multimeter, called resolution, quantifies the degree of accuracy of measurements that the instrument can make. Knowing the resolution of the measuring instrument, you can determine whether it can detect a small change in the measured signal.
For example, if the resolution of a DMM is 1 mV for the 4 V range, at 1 V you would see a change of 1 mV (1/1000 of one volt). You wouldn't buy a ruler with one inch (or one centimeter) divisions if you wanted to measure to a quarter inch (or one millimeter).
A thermometer that measures body temperature only in whole degrees will be of little use, given that normal temperature body is 36.6 °C. You need a thermometer with a resolution of one tenth of a degree.
The terms "digits" and "counts" are used to characterize the resolution of the measuring instrument. DMMs are classified by the number of counts or digits they display. The meter, with 3 and 1⁄2 digit resolution, displays three full digits in the range 0 to 9 and one "half digit" that displays only a "1" or the digit remains blank.
The meter with 3 and 1⁄2 digit resolution displays up to 1999 counts of resolution. The meter with 4 and 1⁄2 digit resolution displays up to 19,999 counts of resolution.
The characteristic of the measuring device in resolution readings is more accurate than in bits. Modern 3-digit and 1⁄2-digit meters can have even higher resolution up to 3200, 4000 or 6000 counts. For some measurements, instruments with 3200 counts provide higher resolution.
For example, measuring device with 1999 counts will not be able to measure to one tenth of a volt if you are measuring voltages of 200 V or more. However, a 3200-count meter will display one tenth of a volt up to 320V. If you measure up to 320V, the resolution is no different than more expensive 20,000-count meters.
Error
An error is the largest allowable error that occurs under certain operating conditions. In other words, this is a designation of how close the values displayed by the measuring device are to the actual value of the measured signal.
DMM accuracy is usually expressed as a percentage of reading. An error equal to one percent of the reading indicates that for a displayed value of 100 V, the actual voltage value can be anything between 99 and 101 V.
Specifications may also specify a range of digits that is added to basic characteristic errors. This value indicates the number of counts by which the rightmost digit on the display can change. Thus, the error from the previous example can be expressed as ± (1% + 2). Thus, for a displayed value of 100 V, the actual voltage value will be between 98.8 and 101.2 V.
The characteristics of an analog meter are given by the error relative to full scale, not relative to the displayed value. The typical accuracy of an analog meter is ±2% or ±3% of full scale. An error of one tenth of full scale becomes an error of 20 to 30% of reading.
Typical DMM intrinsic error is within ±(0.7% + 1) to ±(0.1% + 1) of reading and below.
Ohm's law
Voltage, current and resistance in any part of an electrical circuit can be calculated using Ohm's law, which relates voltage, current and resistance. From school course physics knows that voltage is equal to current times resistance (see Fig. 1).
Thus, if any two values in a formula are known, the third value can be determined. The DMM uses Ohm's Law to directly measure and display resistance, current, or voltage values. Below you will learn how to use digital multimeter For quick receipt the necessary information.
, ammeter and ohmmeter. Sometimes a multimeter is made in the form of current clamps. There are digital and analog multimeters.
A multimeter can be as easy portable device used for basic measurements and troubleshooting, to a sophisticated stationary instrument with many possibilities.
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Digital multimeters
The simplest digital multimeters are portable. Their bit depth is 2.5 digital bits (accuracy is usually about 10%). The most common devices with a capacity of 3.5 (accuracy is usually about 1.0%). There are also slightly more expensive 4.5 digit instruments (usually about 0.1% accurate) and significantly more expensive 5 digit and higher instruments (for example, the Keysight Technologies 3458A precision multimeter (until November 3, 2014, Agilent Technologies) has 8.5 digits). Among such multimeters are found as portable devices powered by galvanic cells, as well as stationary devices operating from the mains alternating current. The accuracy of multimeters with a capacity of more than 5 is highly dependent on the measurement range and the type of measured value, therefore it is negotiated separately for each subrange. IN general case the accuracy of such devices can exceed 0.01% (even for portable models).
Many digital voltmeters (for example, V7-22A, V7-40, V7-78 / 1, etc.) are essentially also multimeters, since they are able to measure, in addition to DC and AC voltage, also resistance, DC and AC current, and some models also provide measurement of capacitance, frequency, period, etc.). Also, scopometers (oscilloscopes-multimeters) can be attributed to a variety of multimeters, combining a digital (usually two-channel) oscilloscope and a fairly accurate multimeter in one case. Typical representatives of scopmeters are AKIP-4113, AKIP-4125, handheld oscilloscopes of the U1600 series from Keysight Technologies, etc.).
The digit capacity of a digital meter, for example, "3.5" means that the meter display shows 3 full digits, with a range from 0 to 9, and 1 digit with a limited range. So, a device of the “3.5 digit” type can, for example, give readings in the range from 0.000 to 1.999, when the measured value goes beyond these limits, switching to another range (manual or automatic) is required.
Indicators of digital multimeters (as well as voltmeters and scopmeters) are made on the basis of liquid crystals (both monochrome and color) - APPA-62, V7-78/2, AKIP-4113, U1600, etc., LED indicators - V7- 40, gas-discharge indicators - B7-22A, electroluminescent displays (ELD) - 3458A, as well as vacuum luminescent indicators (VFD) (including color ones) - B7-78/1.
The typical accuracy of digital multimeters when measuring resistance, DC voltage and current is less than ± (0.2% +1 unit of the least significant digit). When measuring AC voltage and current in the frequency range 20 Hz ... 5 kHz measurement error ± (0.3% + 1 unit of the least significant digit). In the range high frequencies up to 20 kHz when measuring in the range from 0.1 of the measurement limit and above, the error increases much, up to 2.5% of the measured value, at a frequency of 50 kHz it is already 10%. As the frequency increases, the measurement error increases.
Input impedance digital voltmeter about 11 MΩ (does not depend on the measurement limit, unlike analog voltmeters), capacitance - 100 pF, voltage drop when measuring current is not more than 0.2 V. Portable multimeters are usually powered by a 9V battery. Current consumption does not exceed 2 mA when measuring constant voltage and currents, and 7 mA when measuring resistance and variable voltages and currents. The multimeter is usually operational when the battery is discharged to a voltage of 7.5 V.
The number of digits does not determine the accuracy of the instrument. The accuracy of measurements depends on the accuracy of the ADC, on the accuracy, thermal and temporal stability of the applied radio elements, on the quality of protection against external interference, on the quality of the calibration performed.
Typical measuring ranges, for example for the common multimeter M832:
- DC voltage: 0..200 mV, 2 V, 20 V, 200 V, 1000 V
- AC voltage: 0..200 V, 750 V
- DC current: 0..2 mA, 20 mA, 200 mA, 10 A (typically via separate input)
- alternating current: no
- resistance: 0..200 Ohm, 2 kOhm, 20 kOhm, 200 kOhm, 2 MOhm.
Analog multimeters
Device
An analog multimeter consists of a pointer magnetoelectric measuring device (microammeter), a set of additional resistors for measuring voltage and a set of shunts for measuring current. In the mode of measuring alternating voltages and currents, the microammeter is connected to resistors through rectifier diodes. Resistance measurement is performed using the built-in power supply, and resistance measurement over 1..10 MΩ - from an external source.
Features and disadvantages
- Not high enough input impedance in voltmeter mode.
- Non-linear scale in some modes.
- Correct polarity is required.
Basic measurement modes
- ACV (English alternating current voltage - alternating current voltage) - measurement of alternating voltage.
- DCV (English direct current voltage - voltage direct current) - measurement of direct voltage.
- DCA (English direct current amperage - direct current strength) - measurement of direct current.
- Ω - measurement of electrical resistance.
Additional functions
In some multimeters, the following functions are also available:
- Measurement of alternating current.
- Calling - measurement of electrical resistance with sound (sometimes light) alarm of low circuit resistance (usually less than 50
Measured quantities cannot be determined with absolute certainty. Measuring tools and systems always have some tolerance and interference, which is expressed in terms of the degree of inaccuracy. In addition, it is necessary to take into account the features of specific devices.
The following terms are often used in relation to measurement inaccuracy:
- Error- error between true and measured value
- Accuracy— random spread of measured values around their mean
- Permission— the smallest recognizable value of the measured value
Often these terms are confused. Therefore, here I would like to consider the above concepts in detail.
Measurement inaccuracy
Measurement inaccuracies can be divided into systematic and random measurement errors. Systematic errors are caused by gain deviations and zeroing of the measuring equipment. Random errors are caused by noise and/or currents.
Often the concepts of error and accuracy are considered as synonyms. However, these terms are completely various meanings. The error indicates how close the measured value is to its actual value, i.e. the deviation between the measured value and the actual value. Accuracy refers to random spread measured quantities.
When we take a certain number of measurements until the voltage stabilizes or some other parameter, then some variation will be observed in the measured values. This is caused by thermal noise in the measuring circuit of the measuring equipment and the measuring setup. The chart below shows these changes.
Definitions of uncertainties. On the left is a series of measurements. On the right are the values in the form of a histogram.
bar chart
The measured values can be displayed as a bar graph, as shown on the right in the figure. The bar graph shows how often the measured value is observed. The highest point on the histogram is the most frequently observed measured value, in the case of a symmetrical distribution it is equal to the mean value (shown as a blue line on both graphs). The black line represents the true value of the parameter. The difference between the average of the measured value and the true value is the error. The width of the histogram shows the spread of the individual measurements. This variation in measurements is called accuracy.
Use the right terms
Accuracy and accuracy thus have different meanings. Therefore, it is possible that the measurement is very accurate, but has an error. Or vice versa, with a small error, but not exact. In general, a measurement is considered reliable if it is accurate and has a small margin of error.
Error
The error is an indicator of the correctness of the measurement. Due to the fact that in one measurement the accuracy affects the error, the average of a series of measurements is taken into account.
The error of a measuring instrument is usually given by two values: the error of indication and the error on the entire scale. These two characteristics together determine the total measurement error. These measurement errors are given as a percentage or in ppm (parts per million, parts per million) relative to the current national standard. 1% corresponds to 10000 ppm.
The accuracy is given for the specified temperature ranges and for certain period time after calibration. Please note that in different ranges, various errors are possible.
Indication error
The indication of percentage deviation without further specification also applies to the indication. Voltage divider tolerances, amplification accuracy, and absolute readout and digitization tolerances are the causes of this error.
Inaccuracy of indications in 5% for a value of 70 V
A voltmeter that reads 70.00V and has a specification of "±5% of reading" will have an error of ±3.5V (5% of 70V). The actual voltage will lie between 66.5 and 73.5 volts.
Full Scale Accuracy
This type of error is due to bias errors and linearity errors in the amplifiers. For devices that digitize signals, there is a non-linearity of the conversion and ADC errors. This characteristic applies to the entire measuring range used.
The voltmeter may have a "3% of scale" characteristic. If 100V (full scale) is selected during measurement, the error is 3% of 100V = 3V regardless of the measured voltage. If the reading is 70 V in this range, then the actual voltage lies between 67 and 73 volts.
Accuracy 3% of span on 100V range
It is clear from the figure above that this type of tolerance is independent of readings. At 0 V, the actual voltage lies between -3 and 3 volts.
Scale error in numbers
Often for digital multimeters, the scale error is given in digits instead of a percentage value.
For a DMM with a 3½ digit display (range -1999 to 1999), the specification may say "+ 2 digits". This means that the indication error is 2 units. For example: if the range is 20 volts (± 19.99), then the scale error is ±0.02 V. The display shows 10.00 and the actual value will be between 9.98 and 10.02 volts.
Measurement error calculation
The reading and span tolerance specifications together define the instrument's total measurement uncertainty. The following calculations use the same values as in the examples above:
Accuracy: ±5% of reading (3% of span)
Range: 100V
Indication: 70 V
The total measurement error is calculated as follows:
In this case, the total error is ±6.5V. true value lies between 63.5 and 76.5 volts. The figure below shows this graphically.
Total imprecision for 5% and 3% of span reading inaccuracies for 100V range and 70V reading
Percent error is the ratio of the error to the reading. For our case:
Numbers
DMMs may have a specification of "± 2.0% reading, + 4 digits". This means that 4 digits must be added to the 2% reading error. As an example, consider the 3½ digit digital indicator again. It reads 5.00V for the selected 20V range. 2% of reading would mean an error of 0.1V. Add to that the numerical error (=0.04V). The total error is therefore 0.14 V. The true value should be between 4.86 and 5.14 volts.
Total error
Often, only the error of the measuring instrument is taken into account. But also, in addition, the errors of measuring instruments, if they are used, should be taken into account. Here are some examples:
Increasing the error when using a probe 1:10
If a probe 1:10 is used in the measurement process, then it is necessary to take into account not only the measuring error of the device. The error is also affected by the input impedance of the device being used and the resistance of the probe, which together make up the voltage divider.
The figure above is schematically shown with a 1:1 probe connected to it. If we consider this probe to be ideal (no connection resistance), then the applied voltage is transferred directly to the input of the oscilloscope. The measurement error is now determined only by the allowable deviations of the attenuator, amplifier and circuits involved in further signal processing and is set by the device manufacturer. (The error is also affected by the resistance of the connection, which forms internal resistance. It is included in the specified tolerances).
The figure below shows the same oscilloscope, but now the 1:10 probe is connected to the input. This probe has an internal connection resistance and, together with the oscilloscope's input resistance, forms a voltage divider. The tolerance of the resistors in the voltage divider is the cause of its own error.
1:10 probe connected to oscilloscope introduces additional error
The oscilloscope's input impedance tolerance can be found in its data sheet. The tolerance of the probe connection resistance is not always given. However, system accuracy is claimed by the manufacturer of a specific oscilloscope probe for a particular type of oscilloscope. If the probe is used with a different type of oscilloscope than the recommended one, then the measurement error becomes undefined. This should always be avoided.
Let's assume that the oscilloscope has a tolerance of 1.5% and a 1:10 probe is used with an error in the system of 2.5%. These two characteristics can be multiplied to obtain the total error of the instrument reading:
Here is a complete error. measuring system, - the error of the reading of the device, - the error of the probe connected to the oscilloscope, of a suitable type.
Shunt Resistor Measurements
Often, when measuring currents, an external shunt resistor is used. The shunt has some tolerance that affects the measurement.
The specified shunt resistor tolerance affects the reading error. To find the total error, the allowable deviation of the shunt and the error in the readings of the measuring device are multiplied:
In this example, the total reading error is 3.53%.
The shunt resistance is temperature dependent. The resistance value is determined for a given temperature. The temperature dependence is often expressed in .
For example, let's calculate the resistance value for temperature environment. The shunt has the characteristics: Ohm(respectively and ) and the temperature dependence 
.
The current flowing through the shunt causes energy to be dissipated in the shunt, which leads to an increase in temperature and, consequently, to a change in the resistance value. The change in resistance value when current flows depends on several factors. For a very accurate measurement, it is necessary to calibrate the shunt for resistance drift and the environmental conditions under which measurements are taken.
Accuracy
Term accuracy is used to express the randomness of the measurement error. The random nature of the deviations of the measured values in most cases has a thermal nature. Due to the random nature of this noise, it is not possible to obtain an absolute error. Accuracy is only given by the probability that the quantity being measured lies within certain limits.
Gaussian distribution
Thermal noise is Gaussian, or, as they say, normal distribution. It is described by the following expression:
Here, is the mean value, shows the variance, and corresponds to the noise signal. The function gives a probability distribution curve as shown in the figure below, where is the mean and the effective noise amplitude is .
The table shows the chances of getting values within the given limits.
As you can see, the probability that the measured value lies in the ± range is equal to .
Accuracy Improvement
Accuracy can be improved by oversampling (changing the sampling rate) or filtering. The individual measurements are averaged, so the noise is significantly reduced. The spread of the measured values is also reduced. When using oversampling or filtering, be aware that this can lead to a decrease in throughput.
Permission
Permission, or, as they say, resolution of the measuring system is the smallest recognizable measurable quantity. The definition of instrument resolution does not refer to measurement accuracy.
Digital measuring systems
The digital system transforms analog signal into digital equivalent through analog-to-digital converter. The difference between the two values, i.e. the resolution, is always one bit. Or, in the case of a digital multimeter, it's a single digit.
It is also possible to express resolution in units other than bits. As an example, consider having an 8-bit ADC. Vertical sensitivity set to 100 mV/div and the number of divisions is 8, the full range is thus 800 mV. 8 bits are represented 2 8 =256 different meanings. The resolution in volts is then 800 mV / 256 = 3125 mV.
Analog measuring systems
In the case of an analog instrument, where the measured value is displayed mechanically, as in a pointer instrument, it is difficult to obtain an exact number for resolution. First, the resolution is limited by mechanical hysteresis caused by the friction of the hand mechanism. On the other hand, the resolution is determined by the observer making his own subjective assessment.
I came across a fact that surprised me and will probably surprise you too. It turns out that measuring the voltage in the network with an accuracy of at least one volt is an almost impossible task.
The six fixtures in this photo show different meanings, and the maximum differs from the minimum by more than 6 volts.
In the process of preparing an article on power meters, I conducted an experiment with simultaneous measurement of the mains voltage by several devices and, having received such different results, I began to deal with accuracy.
Typically, for digital instruments, manufacturers indicate accuracy in the form of ± (0.8% + 10). This entry means plus or minus 0.8% plus 10 low order units. For example, if the device measures voltage and shows integer and tenth values, then at a voltage of 230 volts its accuracy will be ± (230/100 * 0.8 + 10 * 0.1), that is, ± 2.84 V (ten units of the least significant digit in this case are 1 volt).
Sometimes the accuracy is given as ±(0.5FS+0.01). FS is Full Scale . Such a record means that the device may have reading deviations of up to 0.5% of the measurement range limit plus 0.01 volts (if it is a voltmeter). For example, if the range is 750V and ±(0.5FS+0.01) is specified, the deviation can be up to ±(750/100*0.5+0.01), i.e. ±3.76V no matter what voltage is being measured.
There are two unpleasant nuances.
Often in the characteristics of the device, manufacturers indicate general accuracy values for the type of measurement, and on individual ranges, everything can be even worse. So, for my UNI-T UT61E multimeter, which I always considered very accurate, for measuring AC voltage everywhere, including the manufacturer’s website, the accuracy is ± (0.8% + 10), but if you carefully read the instructions, on the 48th page you can find here's a label:
In the range of 750 V at mains frequency, the measurement accuracy is actually ±(1.2%+10), i.e. ±3.76 V at 230 V.
The second nuance is that the recording of accuracy depends on how many decimal places the device shows. ±(1%+20) may be more accurate than ±(1%+3) if the first instrument shows two decimal places and the second one. In the characteristics of devices, the number of decimal places in each range is rarely indicated, so one can only guess about the real accuracy.
From the tablet above, I learned something amazing. It turns out that my UNI-T UT61E at voltages up to 220 volts shows two decimal places, and therefore has an accuracy of ± 1.86 V at a voltage of 220 V, because in this case in the record ± (0.8% + 10) 10 is only 0.1 V , but at a voltage of more than 220 volts, it starts to show one decimal place and the accuracy is more than halved.
Haven't I screwed up your head yet? :)
With my second Mastech MY65 multimeter, things are even more interesting. On its box, the accuracy of measuring AC voltage for the range of 750V ± (0.15% + 3) is indicated. The device in this range has one decimal place, which means the accuracy is something like ± 0.645 V at a voltage of 230 V.
But it was not there! There is an instruction in the box, it already contains ± (1% + 15) on the same range of 750 V, and this is already ± 3.8 V at a voltage of 230 V.
But that's not all. We look at the official site. And there already ± (1.2% + 15), that is, ± 4.26 V at 230 V. The accuracy unexpectedly decreased by almost seven times!
This MY65 is generally strange. Two different multimeters are sold under this name. Here, for example, on the same site green MY65 and yellow MY65 with different possibilities, different design and different parameters.
In Chinese online stores, you often find such a thing for $ 3.5, which is plugged into an outlet and shows voltage.
Do you know how accurate it is? ±(1.5%+2). Now you know how to decipher it. The thing shows whole volts, which means that at a voltage of 230 volts its accuracy is ± (230/100 * 1.5 + 2), that is, ± 5.45 V. As in a joke, plus or minus a tram stop.
So how can you measure the voltage in the network with guaranteed accuracy at least up to a volt in a domestic environment? But no way!
The most accurate multimeter that I could find on the net - UNI-T UT71C costs $ 136 and when measuring AC voltage in the range of 750 V it shows two decimal places and has an accuracy of ± (0.4% + 30), that is, at a voltage of 230 volts ± 1.22 IN.
Actually, it's not all that bad. Many devices have a real accuracy an order of magnitude higher than the declared one. But this accuracy is not guaranteed by the manufacturer. Maybe it will be much more accurate than promised, but maybe not.
P.s. Thanks to Oleg Artamonov for advice while preparing the article.
2016, Alexey Nadezhin
A multimeter, also known as a tester, is a modern measuring device used to measure all the main characteristics electronic circuits. It measures resistance, current, voltage, capacitance and other parameters. Most of the models on the market are able to work with both direct and alternating, that is, sinusoidal, current. Consider what these devices have the main characteristics and how accurate the readings are, depending on the type of device.
Measurement accuracy and bit depth
The multimeter has exactly two main characteristics: the measurement accuracy and the bit depth of the indicator. The simplest and available models differ in low accuracy - the error of indications is about 10%, as well as a bit depth of 2.5. With the growth of the class of the device and its price, the accuracy increases significantly, as well as the bit depth. It should be noted right away that the error of all testers also strongly depends on the type of measurements taken and the range in which the test is carried out. IN best case the error is about 0.01%.
It should be noted such a parameter as the input resistance of the multimeter. The tester circuit is such that the device itself has a certain resistance, which is usually written in technical documents in kiloohms per volt (kOhm / V). Previously, instruments with 10 or 20 kΩ / V were used, with the latter having slightly more accuracy. However, modern devices have hundreds of times higher resistance, which completely eliminates its effect on the accuracy of the readings of the device. In most cases, such a parameter is not even indicated in the instructions for the tester.
Basic signs on the panel
To correctly measure, you need to understand the symbols on the panel of the multimeter. The handle of the device can be in the "off" position - OFF. It can also point to one of the ranges.
The DC voltage measurement mode is designated as DCV, and ACV (also found V~). Direct current measurement zone - DCA. Resistance is traditionally denoted by the Greek letter "omega" - Ω. The connector for the black wire of the probe is designated COM. Usually on the left there is a connector for testing transistors.
These are the main designations, but each model may have its own characteristics and capabilities.
Varieties
Among the entire range of models on the market, two main types of multimeters can be distinguished: digital and analog. Today, it is the first ones that are most often encountered, but classic testers are also in no hurry to become a thing of the past - they are still in demand by professionals.
There are several reasons for this popularity. First of all, the accuracy of digital priors depends on external conditions. It can drop significantly if you have to work in conditions of strong electromagnetic field or radio interference. In addition, they require an additional power source, and as it fails, the readings deviate more and more from the exact ones.
Analog
The main advantages classic models is reliability and low price. Unfortunately, their accuracy is somewhat lower, and the spread of indicators during measurement, on the contrary, is higher. The error of the average analog multimeter is about 2% of the measurement limit on the scale of the device.
Digital
The main difference is that in digital models all readings are displayed on a liquid crystal display. These devices, unlike analog ones, can boast of greater measurement accuracy, up to 0.5% of the actual value. Besides, digital models different high resolution measuring system. Thus, they provide greater measurement accuracy with big amount decimal places.
Indication
Additional features
In addition to the self-evident current, voltage and resistance, modern models can also make other measurements. These include inductance, capacitance, and with the help of a special sensor or thermocouple, they can also measure temperature. The principle of the advanced model allows you to cope with the measurement of pulse duration, intervals between them, frequency.
Almost all models can produce a circuit check, that is, a check of its integrity. If its resistance falls below a predetermined value, the device emits a sound signal.
Varieties by levels
Today, multimeters are on sale, which can be conditionally divided into several levels, including the price parameter. Before choosing any specific model, it is necessary to determine which parameters and with what accuracy the multimeter will have to measure.
It is also important to pay attention to the battery of the device - multimeters are recommended for finger batteries, since krone-type batteries are more difficult to find, and they cost more.
In the total mass, devices can be divided into three levels according to their characteristics and price:
- elementary. Testers up to 1000 rubles. Most simple appliances little-known brands. Quite often there are curiosities when the same model is sold under discontinuous manufacturers;
- average. Within 3000 rubles. Represented by products of Uni Trend, Mastech, Victor, CEM and the like;
- professional. The most expensive. Testers of this level are released by APPA, Uni Trend, Fluke, CEM.
Let's take a closer look at the characteristics and capabilities of multimeters.
Entry Level Testers
multimeter entry level most commonly purchased for home use. Such models cannot boast of the quality of the probes, the screen, or even the body. Over time, entry-level testers crack and break cables.
When selling such devices, the error is rarely indicated, since in any case it is quite high. But the accuracy of the multimeter is quite enough for home use. Such devices can be called fundamental circuit diagram, the presence of current in the socket has been checked, the voltage has been measured, etc. Considering the areas of use, the requirements for similar devices, are minimal.
Intermediate Testers
Mid-range models are made from more than quality materials, and some are additionally dressed in shockproof case. The wires to the test probes are much longer and stronger. In the manual for mid-range multimeters, the circuit is often indicated, as well as ranges and measurement errors. These models of multimeters are not included in the State Register, so they will be unsuitable for enterprises and those working under a license. The audience of buyers is radio amateurs, small organizations and repair enthusiasts.
The measurement level in these multimeters is about 1000 V and up to 20 A. From additional features highlight automatic selection range, overload protection, non-contact voltage indicator. The average error is about 0.5%.
Professional Models
Multimeters have the highest quality case, most often shockproof, the screen is characterized by maximum information content. Measuring leads are soft and comfortable, retain their strength over time. The instruction indicates all the parameters of the devices, the measurement error is minimal, up to 0.025%.
These multimeters are in demand in enterprises, in the production of electronics. Almost all are included in State Register. Warranty for professional devices reaches 3 years.
Of the additional features: communication with a PC via USB, relative measurement mode, linear scale, reduced power consumption, up to 5 digits of indication, wide range work.
State Register
Separate models of multimeters are included in the state register. The State Register is special list, compiled by Rosstandart, which provides measuring instruments. Each of these devices must be tested in a metrology center or similar laboratory. Strict control is used for instruments subject to the law on the uniformity of measurements. Only such multimeters can be used in military and medical enterprises.
In order to choose a tester for yourself, it is not at all necessary to know the device of the multimeter thoroughly. It is enough to determine what tasks the device will have to perform, as well as what accuracy is required from it. This will allow you to choose best option without overpaying for extra precision in this situation and additional options.
