: the current in the circuit is directly proportional to the voltage and inversely proportional to the resistance.
CURRENT POWER is a quantitative characteristic of an electric current; it is a physical quantity equal to the amount of electricity flowing through the cross-section of a conductor per unit of time. Measured in amperes.
For electrical wiring in an apartment, the current strength plays a huge role, because based on the maximum possible value for a separate line coming from the electrical panel, the cross-section of the conductor and the value of the maximum current of the circuit breaker, which protects the electrical cable from damage in case of occurrence, depend.
Therefore, if the cross-section is not correctly selected and the circuit breaker, it will simply be knocked out, and it will simply not be possible to replace it with a more powerful one.
For example, the most common wires and cables in electrical wiring with a cross section of 1.5 square millimeters are made of copper or 2.5 are made of aluminum. They are rated for a maximum current of 16 Amperes or a power connection of no more than 3 and a half kilowatts. If you connect powerful electrical consumers that exceed these limits, then you cannot simply replace the machine with 25 A - the electrical wiring will not withstand and you will have to shift a copper cable with a cross section of 2.5 square meters from the shield. mm, which is designed for a maximum current of 25 A.
Units for measuring the power of electric current.
In addition to Amperes, We often come across the concept of the power of an electric current. This value shows the work done by the current per unit of time.
Power is equal to the ratio of the work done to the time during which it was done. Power is measured in watts and is denoted by the letter P. It is calculated by the formula P = A x B, that is, in order to find out the power, it is necessary to multiply the voltage value of the mains by the current consumption, electrical appliances connected to it, household appliances, lighting, etc. etc.
On electrical consumers, often on the plates or in the passport, only the power consumption is indicated, knowing which you can easily calculate the current. For example, the power consumption of a TV is 110 watts. To find out the amount of current consumed, divide the power by voltage 220 Volts and we get 0.5 A.
But keep in mind that this is the maximum value, in reality it may be less, since the TV at low brightness and under other conditions will consume less energy.
Instruments for measuring electric current.
In order to find out the real power consumption, taking into account the operation in different modes for electrical appliances, household appliances, etc. - we need electrical measuring devices:
- Ammeter- well-known to everyone from the practical lessons of physics at school (Figure 1). But in everyday life and by professionals, they are not used due to their impracticality.
- Multimeter- this electronic device performs various measurements, including current strength (Figure 2). It is very widespread, both among electricians and in everyday life. How to use it to measure the current strength I have already told you.
- Tester- the same practically as a multimeter, but without the use of electronics with an arrow, which indicates the value of the measurement by divisions on the screen. Rarely seen today, but they were widely used during the Soviet era.
- Measuring Clamps electrician (Figure 3), it is them that I use in my work, because they do not require breaking the conductor for measurement, there is no need to climb under the voltage and disconnect the load. It is a pleasure to measure them - quickly and easily.
How to correctly measure the amperage.
In order to measure the power for consumers, it is necessary to connect one clamp from an ammeter, tester or multimeter to the positive terminal of the battery or the wire from the power supply or transformer, and the second clamp to the wire going to the consumer and after switching on the DC measurement mode with a margin of the upper maximum limit is to take measurements.
Be careful when you open a running circuit, an arc arises, the magnitude of which increases with the amperage.
In order to measure the current for consumers connected directly to an outlet or to an electric cable from a home electrical network, the measuring device is switched to the alternating current measurement mode with a margin at the upper limit. Next, a tester or multimeter is included in the phase wire break. What is the phase we read in.
All work must be carried out only after removing the voltage.
After everything is ready, we turn on and check the current strength. Just make sure that you do not touch exposed contacts or wires.
Agree that the above methods are very inconvenient and even dangerous!
For a long time, in my professional activity as an electrician, I have been using to measure current strength clamp meter(in the picture on the right). They often come in the same case as a multimeter.
To measure them simply - we turn on and switch to the alternating current measurement mode, then we spread the mustache on top and pass the phase wire inside, after that we make sure that they fit snugly against each other and take measurements.
As you can see, it is fast, simple and you can measure the current strength under voltage in this way, just be careful not to accidentally short-circuit adjacent wires in the electrical panel.
Just remember that for correct measurement, you need to girth only one phase wire, and if you clasp a solid cable, in which the phase and zero go together, it will not be possible to carry out measurements!
Related materials:
When checking power electrical circuits, it is often necessary to measure the current strength. To measure the magnitude of a direct current, as a rule, a resistor shunt is used, connected in series with the load, the voltage of which is proportional to the current. However, if it becomes necessary to measure large currents, then a shunt of impressive power will be required, so it is more advisable to use other measurement methods.
In this regard, I had the idea to assemble a current meter based on a Hall sensor. Its diagram is shown in the figure.
Features of the ammeter:
- Measurement of AC or DC current without electrical contact with the circuit
- TrueRMS current measurement regardless of waveform and maximum value over a period (approximately 0.5 seconds)
- Information output to the character LCD display
- Two measurement modes (up to 10A and up to 50A)
The scheme works as follows. The wire with the current is located inside the ferrite ring, thus creating a magnetic field, the magnitude of which is directly proportional to the strength of the current. A Hall sensor located in the air gap of the core converts the field induction into a voltage, and this voltage is fed to the operational amplifiers. Op amps are needed to bring the voltage levels from the sensor to the ADC input voltage range. The received data is processed by the microcontroller and displayed on the LCD display.
Preliminary calculation of the scheme
R20 * 10 * 7 ring made of N87 material was used as a core. Hall sensor - SS494B.
With the help of a needle file, a gap is machined into the ring of such a thickness that the sensor will fit there, that is, about 2 mm. At this stage, it is already possible to roughly estimate the sensitivity of the sensor to current and the maximum possible measured current.
Equivalent permeability of the core with a gap is approximately equal to the ratio of the length of the magnetic line to the value of the gap:
Then, substituting this value into the formula for calculating the induction in the core and multiplying it all by the sensitivity of the sensor, we find the dependence of the output voltage of the sensor on the current strength:
Here K B- the sensitivity of the sensor to the magnetic field induction, expressed in V / T (taken from the datasheet).
For example, in my case ls= 2 mm = 0.002 m,K B= 5 mV / Gauss = 50 V / T, whence we get:
The real sensitivity to current turned out to be equal 0.03V / A, that is, the calculation is very accurate.
According to the datasheet on SS494B, the maximum induction measured by the sensor is 420 Gauss, therefore the maximum measured current is:
Photo of the sensor in the gap:
Calculation of op-amp circuits
The ammeter has two channels: up to 10 A (23 MK output), and up to 50 A (24 MK output). Mode switching is handled by the ADC multiplexer.
An internal reference is selected as the ADC reference voltage, therefore, the signal must be brought to the range of 0 - 2.56 V. When measuring currents of ± 10 A, the sensor voltage is 2.5 ± 0.3 V, therefore, it must be amplified and shifted so that the zero point was exactly in the middle of the ADC range. For this, op-amp IC2: A is used as a non-inverting amplifier. The voltage at its output is described by the equation:
Here, R2 means R2 and P2 connected in series, and R3 means R3 and P3, respectively, so that the expression does not look too cumbersome. To find the resistances of the resistors, write the equation twice (for currents -10A and + 10A):
We know the voltages:
Setting R4 equal to 20 kΩ, we obtain a system of two equations, where the variables are R2 and R3. The solution to the system can be easily found using mathematical packages, for example MathCAD (the calculation file is attached to the article).
The second circuit consisting of IC3: A and IC3: B is calculated in the same way. In it, the signal from the sensor first passes through the follower IC3: A, and then goes to the divider on the resistors R5, R6, P5. After the signal is attenuated, it is further biased by the op-amp IC3: B.
Description of the microcontroller
The ATmega8A microcontroller processes the signals from the op-amp and displays the results on the display. It is clocked by an internal 8 MHz oscillator. Fuses are standard, except for CKSEL. In PonyProg, they are exposed like this:
The ADC is configured to operate at 125 kHz (division ratio is 64). At the end of the ADC conversion, the interrupt handler is called. It stores the maximum current value, and also sums the squares of the currents of successive samples. As soon as the number of samples reaches 5000, the microcontroller calculates the RMS current value and displays the data on the display. Then the variables are reset and everything happens from the beginning. The diagram shows the WH0802A display, but any other display with the HD44780 controller can be used.
Microcontroller firmware, a project for CodeVision AVR and a simulation file in Proteus are attached to the article.
Setting up a schema
Setting up the device comes down to adjusting the trimming resistors. First you need to adjust the display contrast by turning P1.
Then, by switching the S1 button to the mode up to 10A, we set P2 and P3. We unscrew one of the resistors to the right as far as possible and, rotating the second resistor, we achieve zero readings of the device. We are trying to measure the current, the value of which is known exactly, while the ammeter readings should turn out to be lower than it actually is. We twist both resistors slightly to the left, so that the zero point is preserved, and again we measure the current. This time the reading should be slightly larger. We continue this until we achieve an accurate display of the current value.
Now let's switch to the mode up to 50A and configure it. With resistor P4 we set zero on the display. We measure any current and look at the readings. If the ammeter overestimates them, then turn P5 to the left; if it underestimates, then turn to the right. Again we set zero, check the readings at a given current, and so on.
Device photo
DC current measurement:
Due to insufficiently accurate calibration, the values are slightly overestimated.
Measuring alternating current with a frequency of 50 Hz, an iron is used as a load:
In theory, the rms sinusoid current is 0.707 of the maximum, but judging by the readings, this coefficient is 0.742. After checking the voltage waveform in the network, it turned out that it only resembles a sinusoid. Considering this, such readings of the device look quite reliable.
The device still has a drawback. Noises are constantly present at the sensor output. Passing through the op-amp, they get to the microcontroller, as a result of which it is impossible to achieve ideal zero (instead of zero, approximately 30-40 mA RMS is displayed). This can be corrected by increasing the capacitance C7, but then the frequency characteristics will deteriorate: at high frequencies, the readings will be underestimated.
Used sources
List of radioelements
| Designation | A type | Denomination | Quantity | Note | Score | My notebook |
|---|---|---|---|---|---|---|
| IC1 | MK AVR 8-bit | ATmega8A | 1 | DIP-28 | Into notepad | |
| IC2, IC3 | Operational amplifier | MCP6002 | 2 | SOIC-8 | Into notepad | |
| IC4 | Linear regulator | L78L05 | 1 | Into notepad | ||
| IC5 | Hall Sensor | SS494B | 1 | Into notepad | ||
| C1-C7 | Capacitor | 100 nF | 9 | K10-17b | Into notepad | |
| R1, R3, R6, R9 | Resistor | 10 kΩ | 4 | SMD 1206 | Into notepad | |
| R2 | Resistor | 12 kΩ | 1 | SMD 1206 | Into notepad | |
| R4 | Resistor | 20 kΩ | 1 | SMD 1206 | Into notepad | |
| R5 | Resistor | 6.8 k Ohm | 1 | SMD 1206 | Into notepad | |
| R7, R8 | Resistor | 100 kΩ | 2 | SMD 1206 | Into notepad | |
| P1 | Trimmer resistor | 10 kΩ | 1 | 3362P | Into notepad | |
| P2 | Trimmer resistor | 4.7 k Ohm | 1 | 3362P |
Current measurement(abbreviated - current measurement) is a useful skill that will come in handy more than once in life. It is necessary to know the magnitude of the current strength when it is necessary to determine the power consumption. A device called an Ammeter is used to measure current.
There is an alternating current and a direct current, therefore, various measuring instruments are used to measure them. The current is always denoted by the letter I, and its strength is measured in Amperes and is denoted by the letter A. For example, I = 2 A shows that the current in the tested circuit is 2 Amperes.
Let us consider in detail how various measuring instruments are marked for measuring different types of currents.
- On a DC current meter, a "-" symbol is inscribed in front of the letter A.
- On the AC meter, the "~" symbol is inscribed in the same place.
- ~ A device for measuring alternating current.
- -A device for measuring direct current.
Here is a photo of an ammeter designed for DC current measurement.
According to the law, the strength of the current flowing in a closed circuit at any point is equal to the same value. As a result, in order to measure the current, it is necessary to disconnect the circuit at any site convenient for connecting a measuring device.
It should be remembered that the magnitude of the voltage present in the electrical circuit does not have any effect on current measurement... The source of current can be either a 220 V household power supply, or a 1.5 V battery, etc.
When you are going to measure the current in a circuit, pay careful attention to what current flows in the circuit, direct or alternating. Take an appropriate measuring device and if you do not know the estimated current in the circuit, put the switch for measuring the current in the maximum position.
Let's consider in detail how to measure the current strength with an electrical appliance.
For safety current consumption measurements with electrical appliances we will make a homemade extension cord with two sockets. After assembly, we get an extension cord very similar to a standard store extension cord.
But if you disassemble and compare with each other, a home-made and store-bought extension cord, then we will clearly see the differences in the internal structure. The conclusions inside the sockets of the homemade extension cord are connected in series, and in the store they are connected in parallel.
The photo clearly shows that the upper terminals are interconnected with a yellow wire, and the mains voltage is supplied to the lower terminals of the sockets.
Now we start measuring the current, for this we insert the plug of the electrical appliance into one of the sockets, and the ammeter probes into the other outlet. Before measuring current, do not forget the information we have read about how to measure the current correctly and safely.
Now let's look at how to correctly interpret the readings of the dial ammeter. At current consumption measurement of the instrument, the ammeter arrow stopped at division 50, the switch was set to the maximum measurement limit of 3 Amperes. The scale of my ammeter has 100 divisions. This means that it is easy to determine the measured current strength by the formula (3/100) X 50 = 1.5 Amperes.
The formula for calculating the power of the device by the consumed current.
Having data on the size of the current consumed by any electrical device (TV, refrigerator, iron, welding, etc.), you can easily determine what power consumption this electrical device has. There is a physical law in the world, to which electricity always obeys. The discoverers of this pattern are Emil Lenz and James Joule, and in honor of them, it is now called the Joule-Lenz Law.
- I - current strength, measured in Amperes (A);
- U is the voltage measured in Volts (V);
- P is the power measured in Watts (W).
Let's carry out one of the calculations of the current.
I measured the current consumption of the refrigerator and it is equal to 7 Amperes. The voltage in the network is 220 V. Therefore, the power consumption of the refrigerator is 220 V X 7 A = 1540 W.
- Tutorial
Introduction
Hello everyone! After the completion of the cycle on the sensors, there were questions of a different plan for measuring the parameters of consumption of household and not very electrical appliances. Who consumes how much, how what to connect to measure, what are the subtleties and so on. It's time to reveal all the cards in this area.In this series of articles, we will look at the topic of measuring electricity parameters. There are actually a very large number of these parameters, which I will try to gradually tell you about in small series.
So far there are three episodes in the plans:
- Measurement of electricity.
- Power quality.
- Devices for measuring the parameters of electricity.
Based on the results of the entire cycle, we will make a kind of smart electric meter with Internet access. Quite ardent lovers of controlling the electrical appliances of their smart home can provide all possible assistance in the implementation of the communication part on the basis of, for example, MajorDomo. Let's make OpenSource smart home better, so to speak.
In this series, we'll cover the following questions in two parts:
- Connection of current and voltage sensors in DC devices, as well as single-phase and three-phase AC circuits;
- Measurement of effective values of current and voltage;
- Power factor measurement;
- Full, active and reactive power;
- Electricity consumption;
1. Connecting sensors
In the last cycle about voltage and current sensors, I talked about the types of sensors, but did not talk about how to use them and where to put them. It's time to fix it
Connecting DC Sensors
It is clear that the entire cycle will be devoted to AC systems, but we will quickly go over DC circuits as well, as this can be useful to us when developing DC power supplies. Take a classic PWM buck converter for example:
Fig 1. Buck converter with PWM
Our task is to provide a stabilized output voltage. In addition, on the basis of information from the current sensor, it is possible to control the operating mode of the choke L1, preventing its saturation, and also to implement current protection of the converter. And to be honest, there are no special options for installing sensors.
A voltage sensor in the form of a resistive divider R1-R2, which is the only one capable of operating on direct current, is installed at the output of the converter. As a rule, a specialized converter microcircuit has a feedback input, and makes every effort to ensure that a certain voltage level, prescribed in the documentation for the microcircuit, appears at this input (3). For example 1.25V. If our output voltage matches this level - everything is fine - we directly apply the output voltage to this input. If not, then set the divisor. If we need to provide an output voltage of 5V, then the divider must provide a division factor of 4, that is, for example R1 = 30k, R2 = 10k.
The current sensor is usually installed between the power supply and the converter and on the microcircuit. By the potential difference between points 1 and 2, and with a known resistance, the resistors Rs can determine the current value of the current of our choke. Installing a current sensor between the sources and the load is not a good idea, since the filter capacitor will be cut off by the resistor from the impulse current consumers. Installing a resistor in the break of the common wire also bodes well - there will be two ground levels with which it is still a pleasure to tinker.
Voltage drop problems can be avoided by using non-contact current sensors such as hall sensors:
Fig 2. Non-contact current sensor
However, there is a trickier way to measure current. Indeed, the voltage drops across the transistor in exactly the same way and the same current flows through it as the inductance. Therefore, by the voltage drop across it, you can also determine the current value of the current. To be honest, if you look at the internal structure of converter microcircuits, for example, from Texas Instruments, then this method occurs just as often as the previous ones. The accuracy of this method is certainly not the highest, but this is quite enough for the current cutoff to work.
Fig 3. Transistor as a current sensor
We do the same in other circuits of similar converters, be it boost or inverting.
However, it is necessary to separately mention the transformer forward and flyback converters.
Fig 4. Connection of current sensors in flyback converters
They can also use either an external resistance or a transistor in its role.
This completes the connection of sensors to DC / DC converters. If you have any suggestions for other options, I will gladly supplement the article with them.
1.2 Connecting sensors to single-phase AC circuits
In AC circuits, we have a much larger selection of possible sensors. Let's consider several options.The simplest is to use a resistive voltage divider and a current shunt.
Fig 5 Connection of resistor sensors
However, she has a couple of significant disadvantages:
First, either we will provide a significant signal amplitude from the current shunt, having allocated a large amount of power on it, or we will be content with a small signal amplitude and subsequently amplify it. And secondly, the resistor creates a potential difference between the neutral of the network and the neutral of the device. If the device is isolated, it does not matter, if the device has a ground terminal, then we risk being left without a signal from the current sensor, since we will short-circuit it. Perhaps it is worth trying sensors that work on other principles.
For example, we will use current and voltage transformers, or a hall effect current sensor and a voltage transformer. There are much more opportunities for working with equipment, since the neutral wire has no losses, and most importantly, in both cases there is a galvanic isolation of the measuring equipment, which can often come in handy. However, it must be borne in mind that transformer current and voltage sensors have a limited frequency response and if we want to measure the harmonic composition of distortions, then this is not a fact for us.
Fig. 6 Connection of transformer and proximity sensors of current and voltage
1.3 Connecting sensors to polyphase circuits of alternating current networks
In multi-phase networks, our ability to connect current sensors is slightly less. This is due to the fact that it will not work at all to use the current shunt, since the potential difference between the phase shunts will fluctuate within hundreds of volts and I do not know of a single general-purpose controller whose analog inputs are capable of withstanding such mockery.One way to use current shunts is of course - for each channel it is necessary to make a galvanically isolated analog input. But it is much easier and more reliable to use other sensors.
In my quality analyzer I use resistive voltage dividers and external hall effect current sensors.
Figure 7 Current sensors in a three-phase network
As you can see from the picture, we are using a four-wire connection. Of course, instead of hall effect current sensors, you can take current transformers or Rogowski loops.
Instead of resistive dividers, voltage transformers can be used for both four-wire and three-wire systems.
In the latter case, the primary windings of the voltage transformers are connected with a delta, and the secondary with a star, the common point of which is the common point of the measuring circuit
Figure 8: Using voltage transformers in a three-phase network
2 RMS value of current and voltage
It's time to solve the problem of measuring our signals. First of all, the effective value of current and voltage is of practical importance for us.
Let me remind you of the materiel from the sensor cycle. Using the ADC of our microcontroller, at regular intervals, we will record the instantaneous voltage value. Thus, for the measurement period, we will have an array of data on the level of the instantaneous voltage value (for current, everything is the same).
Fig 9. Series of instantaneous voltage values
Our task is to calculate the effective value. First, let's use the integral formula:
(1)In a digital system, you have to limit yourself to a certain quantum of time, so we go to the sum:
(2)Where is the sampling period of our signal, and is the number of samples for the measurement period. Somewhere here, in the video, I begin to rub the game about equality of areas. I should have slept that day. =)
In the MSP430FE4252 microcontrollers, which are used in single-phase Mercury electricity meters, 4096 readings are made for a measurement period of 1, 2 or 4 seconds. We will rely on T = 1c and N = 4096 in the future. Moreover, 4096 points per second will allow us to use fast Fourier transform algorithms to determine the harmonic spectrum up to the 40th harmonic, as required by GOST. But more on that in the next series.
Let's sketch out the algorithm for our program. We need to ensure a stable start of the ADC every 1/8192 second, since we have two channels and we will measure this data alternately. To do this, set the timer and the interrupt signal will automatically restart the ADC. All ADCs can do this.
We will write the future program on arduino, since many have it at hand. We have a purely academic interest so far.
Having a 16MHz system quartz frequency and an 8-bit timer (so that life does not seem like honey), we need to ensure the frequency of operation of at least any timer interrupt with a frequency of 8192Hz.
We are sad about the fact that 16MHz is not divided as a whole as we need, and the final frequency of the timer is 8198Hz. Close our eyes to 0.04% error and still read 4096 samples per channel.
We are sad about the fact that the overflow interrupt in arduino is busy timing (responsible for millis and delay, so this will stop working normally), so we use the comparison interrupt.
And we suddenly realize that the signal is bipolar, and that the msp430fe4252 copes with it perfectly. We are content with a unipolar ADC, so we assemble a simple bipolar-to-unipolar converter on an operational amplifier:
Fig 10 Bipolar to unipolar converter
Moreover, our task is to ensure the oscillation of our sinusoid relative to half of the reference voltage - then we either subtract half of the range or activate the option in the ADC settings and get signed values.
The Arduino has a 10-bit ADC, so we subtract half from the unsigned result in the range of 0-1023 and get -512-511.
We check the model assembled in LTSpiceIV and make sure that everything works as it should. In the video, we are additionally convinced experimentally.
Fig 11 simulation result. Green is the source signal, blue is the output
Arduino sketch for one channel
void setup () (autoadcsetup (); DDRD | = (1<
The program was written in the Arduino IDE for the ATmega1280 microcontroller. On my debug board, the first 8 channels are routed for the internal needs of the board, so the ADC8 channel is used. It is possible to use this sketch for a board with an ATmega168, however, you must select the correct channel.
Inside the interrupts, we juggle a couple of service pins to clearly see the working digitizing frequency.
A few words about where the 102 coefficient came from. At the first start, a signal of various amplitudes was supplied from the generator, the actual voltage value was read from the oscilloscope, and the calculated value in absolute ADC units was taken from the console.
| Umax, V | Urms, B | Counted |
| 3 | 2,08 | 212 |
| 2,5 | 1,73 | 176 |
| 2 | 1,38 | 141 |
| 1,5 | 1,03 | 106 |
| 1 | 0,684 | 71 |
| 0,5 | 0,358 | 36 |
| 0,25 | 0,179 | 19 |
Dividing the values of the third column by the values of the second, we get an average of 102. This will be our "calibration" factor. However, you can see that the accuracy drops sharply with decreasing voltage. This is due to the low sensitivity of our ADC. In fact, 10 digits for accurate calculations are catastrophically small and if the voltage in the outlet is measured in this way it will work out, then putting a 10-bit ADC to measure the current consumed by the load will be a crime against metrology.
We will interrupt at this point. In the next part, we will consider the other three questions of this series and we will smoothly move on to creating the device itself.
The presented firmware, as well as other firmware for this series (since I shoot videos faster than preparing articles), can be found in the repository on GitHub.
The load in an electrical circuit is characterized by the strength of the current, the measurement of the current in amperes. Amperage sometimes has to be measured to check the allowable load on the cable. Cables of different cross-sections are used for laying the electric line. If the cable works with a load higher than the permissible value, then it heats up, and the insulation gradually collapses. As a result, this leads to and replacement of the cable.
- After laying a new cable, it is necessary to measure the current passing through it with all electrical devices working.
- If an additional load is connected to the old wiring, then you should also check the current value, which should not exceed the permissible limits.
- With a load equal to the upper permissible limit, the compliance of the current flowing through is checked. Its value should not exceed the rated value of the operating current of the machines. Otherwise, the circuit breaker will de-energize the network due to overload.
- Current measurement is also necessary to determine the operating modes of electrical devices. Measurement of the current load of electric motors is carried out not only to check their operability, but also to detect if the load is higher than the permissible one, which may arise due to a large mechanical force during the operation of the device.
- If you measure the current in the working circuit, then it will show serviceability.
- The functionality in the apartment is also checked by measuring the current.
Power current
In addition to the current strength, there is the concept of current power. This parameter defines the work of the current performed per unit of time. The current power is equal to the ratio of the work performed to the time interval during which this work was performed. Indicated by the letter "P" and measured in watts.
Power is calculated by multiplying the mains voltage by the current consumed by the connected electrical devices: P = U x I. Usually, electrical appliances indicate the power consumption, which can be used to determine the current. If your TV has a power of 140 W, then to determine the current, we divide this value by 220 V, as a result we get 0.64 amperes. This is the maximum current value, in practice the current may be less when the screen brightness is lowered or other settings are changed.
Measuring current with instruments
To determine the consumption of electrical energy, taking into account the operation of consumers in different modes, electrical measuring devices are needed that can measure the parameters of the current.
- ... To measure the magnitude of the current in the circuit, special devices called ammeters are used. They are connected to the measured circuit in a sequential scheme. The internal resistance of the ammeter is very small, so it does not affect the parameters of the circuit. The scale of the ammeter can be marked in amperes or other fractions of an ampere: microamperes, milliamperes, etc. There are several types of ammeters: electronic, mechanical, etc.
- is an electronic measuring device capable of measuring various parameters of an electrical circuit (resistance, voltage, wire breakage, battery suitability, etc.), including current strength. There are two types of multimeters: digital and analog. The multimeter has various measurement settings.
The procedure for measuring current strength with a multimeter
- Find out what is the measurement interval of your multimeter. Each device is designed to measure current in a certain interval, which must correspond to the measured electrical circuit. The highest permissible measuring current must be specified in the instructions.
- Select the appropriate measurement mode. Many multimeters are capable of operating in different modes and measuring different quantities. To measure the current strength, you need to switch to the appropriate mode, taking into account the type of current (direct or alternating).
- Set the required measurement interval on the device. It is better to set the upper limit of the amperage slightly higher than the expected value. You can lower this limit at any time. But there will be a guarantee that you will not disable the device.
- Insert the test plugs of the leads into the sockets. The set of the device includes two wires with probes and connectors. The slots must be marked on the device or shown in the passport.
- To start measuring, you need to connect a multimeter to the circuit. In this case, you should observe safety rules and do not touch live parts with unprotected parts of the body. Do not measure in a humid environment, as the moisture conducts an electric current. Wear rubber gloves on your hands. To break the circuit for measurement, cut the conductor and strip the insulation at both ends. Then connect the test leads of the multimeter to the stripped ends of the wire and make sure that the connection is good.
- Switch on the power supply of the circuit and record the readings of the device. If necessary, correct the upper limit of measurements.
- Disconnect circuit power and disconnect the multimeter.
- ... If you need to measure current without breaking the electrical circuit, then the measuring clamp will be an excellent option for this task. This device is produced in several types, and of different designs. Some models can measure other circuit parameters as well. It is very convenient to use the current clamp.
Current measurement methods
To measure the current in an electrical circuit, you need to connect one terminal of an ammeter or other device capable of measuring current strength to the positive terminal of the current source or, and the other terminal to the consumer's wire. After that, you can measure the current.
When measuring, it is necessary to be careful, as an electric arc can occur when an active electrical circuit is opened.
To measure the current strength of electrical devices connected directly to an outlet or cable of a household network, the measuring device is set to the alternating current mode with an overestimated upper limit. Then the measuring device is connected to the phase wire break.
All work on connecting and disconnecting is allowed only in a de-energized circuit. After all connections, you can apply power and measure the current. In this case, do not touch the bare live parts, in order to avoid electric shock. Such measurement methods are inconvenient and pose a certain hazard.
It is much more convenient to carry out measurements with a clamp meter, which can perform all the functions of a multimeter, depending on the version of the device. It is very simple to work with such mites. It is necessary to set up the measurement mode for direct or alternating current, spread the mustache and cover the phase wire with it. Then you need to check the tightness of the whiskers to each other and measure the current. For correct readings, you only need to cover the phase wire with a mustache. If you cover two wires at once, then the measurement will not work.
The clamp meter is only used for measuring AC parameters. If they are used to measure direct current, then the mustache will be compressed with great force, and it will be possible to move them apart only by turning off the power.
