To measure alternating voltage, analog electromechanical devices (electromagnetic, electrodynamic, rarely inductive), analog electronic devices (including rectifier systems) and digital measuring instruments are used. Compensators, oscilloscopes, recorders and virtual instruments can also be used for measurements.
When measuring alternating voltage, one should distinguish between instantaneous, amplitude, average and effective values of the desired voltage.
Sinusoidal alternating voltage can be represented in the form of the following relationships:
Where u(t)- instantaneous voltage value, V; U m - amplitude voltage value, V; (U - average voltage value, V T - period
(T = 1//) the desired sinusoidal voltage, s; U- effective voltage value, V.
The instantaneous value of the alternating current can be displayed on an electronic oscilloscope or using an analog recorder (chart recorder).
Average, amplitude and effective values of alternating voltages are measured by pointer or digital devices for direct assessment or alternating voltage compensators. Instruments for measuring average and amplitude values are used relatively rarely. Most devices are calibrated in effective voltage values. From these considerations, the quantitative stress values given in textbook, are given, as a rule, in effective values (see expression (23.25)).
When measuring variable quantities, the shape of the desired voltages is of great importance, which can be sinusoidal, rectangular, triangular, etc. The passports for devices always indicate what voltages the device is designed to measure (for example, to measure sinusoidal or rectangular voltages). In this case, it is always indicated which AC voltage parameter is being measured (amplitude value, average value or effective value of the measured voltage). As already noted, for the most part calibration of devices is used in the effective values of the desired alternating voltages. Because of this, all the variable voltages considered below are given in effective values.
To expand the measurement limits of alternating voltage voltmeters, additional resistances, instrument transformers and additional capacitances (with electrostatic system devices) are used.
The use of additional resistances to expand the measurement limits has already been discussed in subsection 23.2 in relation to DC voltmeters and therefore is not considered in this subsection. Voltage and current measuring transformers are also not considered. Information on transformers is given in the literature.
With a more detailed consideration of the use of additional capacitances, one additional capacitance can be used to expand the measurement limits of electrostatistics of voltmeters (Fig. 23.3, A) or two additional containers can be used (Fig. 23.3, b).
For a circuit with one additional capacitance (Fig. 23.3, A) measured voltage U distributed between the voltmeter capacitance C y and additional capacity C is inversely proportional to the values S y and S
Considering that U c = U- Uy, can be written down
Rice. 23.3. Scheme for expanding electrostatic measurement limits
voltmeters:
A- circuit with one additional capacity; b- circuit with two additional containers; U- measured alternating voltage (rms value); C, C, C 2 - additional containers; Cv- capacity of the electrostatic voltmeter used V; U c- voltage drop across additional capacitance C; U v - electrostatic voltmeter reading
Solving equation (23.27) for U, we get:
From expression (23.28) it follows that the greater the measured voltage U Compared to the maximum permissible voltage for a given electrostatic mechanism, the smaller the capacitance should be WITH compared to capacity With u.
It should be noted that formula (23.28) is valid only with ideal insulation of the capacitors forming the capacitors WITH And C v . If the dielectric that insulates the capacitor plates from each other has losses, then additional errors arise. In addition, the voltmeter capacity C y depends on the measured voltage U, since from U The readings of the voltmeter and, accordingly, the relative positions of the moving and fixed plates that form the electrostatic measuring mechanism depend. The latter circumstance leads to the appearance of another additional error.
The best results are obtained if, instead of one additional capacitance, two additional capacitors C (and C 2) are used, forming a voltage divider (see Fig. 23.3, b).
For a circuit with two additional capacitors, the following relation is valid:
Where U a - voltage drop across the capacitor C y
Considering that 
can be written down
Solving equation (23.30) for U, we get:
From expression (23.31) we can conclude that if the capacitance of the capacitor C 2 to which the voltmeter is connected significantly exceeds the capacitance of the voltmeter itself, then the voltage distribution is practically independent of the voltmeter reading. In addition, at C 2 " C y change in insulation resistance of capacitors C, and C 2 and frequency
Table 23.3
Limits and errors of measurement of alternating voltages
the measured voltage also has little effect on the instrument readings. That is, when using two additional containers, additional errors in measurement results are significantly reduced.
Limits for measuring alternating voltages with devices different types and the smallest errors of these devices are given in table. 23.3.
As examples, Appendix 5 (Table A.5.1) shows specifications universal voltmeters that allow you to measure, among other things, alternating voltages.
In conclusion, the following should be noted.
Errors in measuring currents (direct and alternating) with devices of the same type and under equal conditions are always greater than errors in measuring voltages (both direct and alternating). The errors in measuring alternating currents and voltages with devices of the same type and under equal conditions are always greater than the errors in measuring direct currents and voltages.
More detailed information questions raised can be obtained from .
It is hardly an exaggeration to say that every radio amateur has a tester of the M-83x family. Simple, accessible, cheap. Quite sufficient for an electrician.
But for the radio amateur it has a flaw when measuring alternating voltage. Firstly, low sensitivity, and secondly, it is intended for measuring voltages with a frequency of 50 Hz. Often a novice amateur does not have other instruments, but wants to measure, for example, the voltage at the output of a power amplifier and evaluate its frequency response. Is it possible to do this?
On the Internet, everyone repeats the same thing - “no higher than 400 Hz.” Is it so? Let's get a look.
For testing, a setup was assembled from an M-832 tester, a GZ-102 sound generator and
lamp voltmeter V3-38.
Judging by the available data, numerous devices of the M-83x or D-83x family are assembled according to almost the same scheme, so there is a high probability that the measurement results will be close. In addition, in this case, I was of little interest in the absolute error of this tester; I was only interested in its readings depending on the signal frequency.
The level was selected around 8 Volts. This is close to the maximum output voltage of the GZ-102 generator and close to the voltage at the output of an average power UMZCH.
It would be better to make another series of measurements with a powerful ULF loaded onto a step-up transformer, but I don’t think that the results will change dramatically.
For convenience of estimating the frequency response in dB, a level of 0 dB was selected at the 10 V limit of the V3-38 voltmeter. When the signal frequency changed, the level was slightly adjusted, but the changes did not exceed fractions of dB and can be ignored.
results
In the table below TO- coefficient by which the measurement result of the tester at a given frequency must be multiplied, taking into account the decline in the frequency response.
To obtain tabulated results in dB, the voltage level obtained for each frequency was set at the output of the generator, and the difference in dB was read and entered into the table. Some inaccuracies due to 0.5 dB rounding of tube voltmeter readings and rounding of the last digit of tester readings. I think that in this case a systematic error of 1 dB is quite acceptable because it is imperceptible to the ear.
Conclusion
So what happened?The frequency response of the tester is correct not up to 400 Hz, but up to 4...6 kHz; above that the decline begins, which can be taken into account using the table and, therefore, obtain relatively reliable results in the range of 20...20000 Hz and even higher.
In order to assert that the amendments are suitable for all testers, you need to collect statistics. Unfortunately, I don’t have a bag of testers.
We must not forget that the tester measures alternating voltage using a half-wave rectifier circuit with its disadvantages, such as the ability to measure only sinusoidal voltage without a direct component; at a low measured voltage, the error will increase.
How can I improve the M-832 tester for measuring alternating voltages?
You can install an additional “200-20 V” limit switch and another shunt resistor. But this requires disassembling and modifying the tester; you need to understand the circuit and have a calibration device. I think this is inappropriate.Better make a separate attachment that amplifies and rectifies the voltage. The rectified voltage is supplied to the tester, which is turned on to measure DC voltage.
But this is a topic for another article.
Goal of the work- study of metrological characteristics of electronic voltmeters
Familiarize yourself with the equipment used and instructions for its use. Receive a specific assignment from the teacher to complete the work.
Determine the main error of an electronic voltmeter over the measurement range specified by the teacher. Plot on one graph the dependence of the relative and reduced errors on the readings of the electronic voltmeter. Draw a conclusion about the compliance of the voltmeter being verified with its accuracy class.
Determine the amplitude-frequency characteristic of the electronic voltmeter. Plot the frequency response graph and determine the operating frequency band of the voltmeter at the level of frequency response attenuation determined by the regulatory and technical documentation for the voltmeter being verified.
Experimentally evaluate the frequency response digital voltmeter. Conduct a comparative analysis of the amplitude-frequency characteristics of electronic, digital and electromechanical 11 Note 1. Take the results of research on electromechanical voltmeters from laboratory work No. 1, if it was previously performed. voltmeters. Construct graphs of the frequency response of the devices under study.
Measure the voltage with an electronic voltmeter various shapes(sinusoidal, rectangular and triangular) with the same amplitude at frequencies lying in the operating frequency band of this device. Explain and confirm the results obtained with calculations. Draw a conclusion about the influence of the shape of the measured voltage on the readings of an electronic voltmeter.
Description and order of work
Devices used
Electronic voltmeter with analog output - GVT-417V
Universal measuring device with digital display - GDM-8135
Harmonic Signal Generator - SFG-2120
Electronic oscilloscope - GOS-620
Descriptions of the devices are attached at the stand.
To perform the work, use the diagram presented in Fig. 2.1, where GS is a generator (synthesizer) of sinusoidal, rectangular and triangular signals, CV is a digital voltmeter, EV is an electronic voltmeter, ELO is a cathode ray oscilloscope.
1. The main error of the electronic voltmeter determined by comparison method, i.e. by comparing its readings with the readings of a standard, in this case, a digital voltmeter, at a sinusoidal voltage. The readings of the reference voltmeter are taken as the actual voltage values.
The GVT-417B electronic voltmeter is checked at a frequency of 1 kHz on scales with upper limits of 1V or 3V, which is due to the regulation range of the output voltage of the generator used.
Verification is carried out for n= (610) scale marks evenly distributed along the instrument scale, with smooth increase and a decrease in its readings
Verified voltage points U p are installed on the electronic voltmeter being verified, and the actual voltage values U oh uv, U O the value is taken from a standard digital voltmeter, respectively, when approaching the mark being verified U n scales as the readings increase and decrease.
The results of measurements and calculations are presented in the form of a table.
Absolute, relative, reduced errors and variation of readings are determined using the formulas given in laboratory work 1 or in ; also determine the maximum reduced error max = Max(| i|) and maximum variation H max = Max( H i) obtained as a result of the experiment.
Based on the results of tests and calculations, plot on one graph the dependence of the relative and reduced errors on the readings of the electronic voltmeter, = F (U P), = F (U P); The graph also contains lines defining the limits of the maximum permissible reduced error corresponding to the accuracy class of the device being tested.
Based on the analysis of data on the main error and variation of readings, a conclusion is made about the compliance of the specified characteristics with the requirements determined by the accuracy class of the device being tested.
2. Amplitude-frequency characteristic of an electronic voltmeter is defined as the dependence of voltmeter readings on the frequency of the input sinusoidal signal at a constant value of its voltage.
In practice, the concept of the operating frequency band of a measuring instrument is widely used. The operating frequency band of a voltmeter refers to the frequency range f, for which the unevenness of the frequency response of the voltmeter does not exceed a certain pre-established permissible value. Thus, for the GVT-417B electronic voltmeter, within the operating band, no more than a 10 percent change in the instrument readings from the readings at the frequency is allowed f 0 = 1KHz.
The extreme values of the frequency range that satisfy the specified requirement are called the lower f H and top f In the limiting frequencies of the operating band of the electronic voltmeter.
The frequency response is also determined according to the scheme shown in Fig. 2.1. The SFG-2120 generator is used as a signal source, which ensures a constant amplitude of the output signal when the frequency changes in its operating range.
The frequency is preliminarily set on the GS generator f 0 =1kHz with a sinusoidal waveform. Using the GS generator output voltage regulator, set the reading of the electronic voltmeter at the scale mark in the range (0.7-0.9) from the upper measurement limit and record the set voltage value U P ( f 0 =1kHz) = … .
In the future, when determining the frequency response, only the frequency of the GS signal generator is changed, and the voltage taken from the generator is not changed.
To monitor the signal level and its shape, a cathode ray oscilloscope is used. On the oscilloscope screen, by selecting the deviation coefficients (VOLTS/DIV) and sweep coefficients (TIME/DIV), an oscillogram convenient for observations and measurements is obtained - an image of several periods of a sinusoid with a sufficiently large amplitude; record the amplitude l A (or l 2A - double amplitude) image of the signal for subsequent monitoring of the signal level.
It is convenient to determine the frequency response separately for the high- and low-frequency regions.
In the high-frequency region, the frequency response begins to be taken in steps of 100 kHz: 1 kHz (initial frequency), 100 kHz, 200 kHz, ... until the frequency at which the readings of the electronic voltmeter drop to a value of the order of 0.8-0.9 from the initially set reading U P ( f 0 =1kHz). To clarify the upper frequency f in the operating frequency band f electronic voltmeter in the region of a 10 percent decline in the frequency response, it is necessary to additionally remove several points of the frequency response with a smaller step in changing the frequency of the input signal.
During testing, the constant level of the GS output signal is monitored with an electronic oscilloscope.
Write the results of tests and calculations in the table:
For EV f B = ... for CV f B = ...
Where U P ( f) - voltmeter readings at frequency f; K(f) = U P ( f) /U P ( f o = 1 kHz) - frequency response of the voltmeter, presented in relative units for the corresponding frequencies, f c is the upper limiting frequency of the voltmeter’s operating band, found in the experiment.
When performing a task in a similar way at the same frequencies, the frequency response of a digital voltmeter is evaluated. The test results are entered into the same table. Since this work requires comparing the operating frequency bands of electronic and digital voltmeters in a qualitative sense, it is not necessary to clarify the frequency response of a digital voltmeter at additional frequency points. In this case, the values of the limiting frequencies of the digital voltmeter will be determined with less accuracy.
Lower cutoff frequency f n working strip f for electronic AC voltmeters it is usually in the region of units and the first tens of Hz. Therefore, the procedure for determining the frequency response in the low-frequency region can be as follows: first, reduce the frequency from the original f 0 =1000Hz through 200Hz, and then from 50Hz through 10Hz. If necessary, clarify the lower frequency f n of the working band, at which the frequency response drops to a level of 0.9 from its value at f 0 =1000Hz, removing additional points in 1Hz increments.
The frequency response of a digital voltmeter is assessed at the same frequencies.
The test and calculation results are presented in table form:
For EV f n = …Hz, for CV f n = ...Hz.
Based on the results of the research, frequency response graphs are constructed for high and low frequencies. It is convenient to construct graphs along the frequency axis on a logarithmic scale.
3. Determination of the influence of the input signal shape on the readings of AC voltmeters.
In electronic AC voltmeters, AC to DC voltage converters are used, as, for example, shown in Fig. 2.2, where: u in( t) - input voltage, U - alternating current amplifier, IM - magnetoelectric measuring mechanism, - deflection angle of the measuring mechanism.
Converters of amplitude, average rectified or effective values of alternating voltage into direct voltage are used. At the same time, all electronic AC voltmeters, regardless of the type of converter, are calibrated in effective values of sinusoidal voltage. This may lead to additional errors when measuring non-sinusoidal voltages.
The GVT-417B electronic voltmeter has an average-rectified value converter. For such voltmeters, the angle of deflection of the pointer is proportional to the average rectified value U cf input voltage
Where: k V- voltmeter conversion coefficient, u in( t) - input alternating voltage with period T.
Indications U p voltmeter are calibrated in current U sinusoidal voltage values
Where: k F = U/U CP - voltage waveform coefficient, for sinusoidal voltage kФ = 1.11. Therefore, for another voltage form ( k F? 1.11) voltmeter readings may differ significantly from its actual value, which leads to an additional error in the measurement result.
In such cases, the required voltages with a known signal shape can be found by calculation.
Based on the principle of operation of the voltmeter and the accepted calibration, it is possible according to the readings U P of the device to determine the average rectified value of any (within the frequency response of the voltmeter) measured voltage
U SR = U P/1.11.
Effective value U non-sinusoidal voltage can only be determined if the coefficient is known k F voltage waveform, k F = U/U CP (or the signal shape is known from which this coefficient can be determined)
U= k F U SR.
Numerical values of shape factors for some signals are presented in the table.
To experimentally evaluate the influence of the voltage shape on the readings of an electronic voltmeter, signals of sinusoidal, rectangular and triangular shapes are sequentially measured at the same amplitude.
Previously, the voltmeter readings are set on the sinusoidal signal in the range of 0.5 - 0.6 from the upper measurement limit of the selected scale at the nominal frequency f n =1 kHz, and then, at the same amplitude of the input signals, the voltage is measured with a voltmeter for other signal forms. Signal shapes (sinusoidal, triangular, rectangular) are set by pressing the “ key Wave” on the generator.
According to indications U The voltmeter determines the average U SR and current U voltage values for all waveforms.
To assess the influence of the voltage form on the readings of an electronic voltmeter with a medium-rectified voltage converter, determine the additional relative error (in percent)
100(U P - U)/U.
The results of measurements and calculations are recorded in a table.
It should be noted that an additional error will be included in the measurement result if the effective values of non-sinusoidal voltages are determined directly from the voltmeter readings without taking into account the signal shape and carrying out the corresponding calculations.
Based on the research results, draw a conclusion about the influence of the shape of the voltage curve on the results of its measurement with an electronic voltmeter.
Literature
Metrology, standardization and certification: a textbook for students. higher textbook institutions/[B.Ya.Avdeev, V.V.Alekseev, E.M.Antonyuk, etc.]; edited by V.V. Alekseev. - M.: Publishing center "Academy", 2007. pp. 136-140.
The uninterrupted operation of electrical appliances largely depends on the voltage level in the network, the correct current supply, and the integrity of the wiring. You can measure AC voltage using a multimeter. This is an indispensable assistant in the timely identification of problems in the electrical network and ensuring safe use household and professional appliances.
Features, functions, types of devices
This device is a universal recorder of many electrical quantities. Depending on the model range and the set of functions that they perform, multimeters have found their use both in everyday life and in the arsenal of professional electricians.
An average-cost multimeter can measure:
- indicator of alternating voltage in the network and constant voltage of the battery or battery;
- direct and alternating current (current strength);
- resistance level;
- operability of diodes (continuity mode);
- current frequency;
- temperature;
- capacitance value of the capacitor.
New-style devices may have a low-frequency generator and a sound probe. Among the entire range of products, it is worth highlighting 2 main types of devices.
Electronic (digital) type. The obtained indicators are displayed on the screen, which is surrounded by indicators from seven segments. Most of them work in automatic mode, the multimeter determines the limiting value of the values independently, based on the data received. You just need to select the type of measurement. Other models can transfer data directly to a computer for further processing.
Arrow type. This type of device will be a real salvation when strong interference disrupts normal functioning electronic multimeter and completely distort the information.
At home, it will be enough to measure current with an electronic type multimeter with a resolution of 3.5. These are devices like dt 831, 832 or the newer modification dt 834.
Housing elements
Since digital models have become increasingly in demand, the designations and main characteristics of multimeters will be discussed using their example.
They are equipped with a liquid crystal screen that displays the measured values. Just below is a switch rotating around its axis. It indicates the selected type and measurement limits.
2 probes with wires are connected to the sockets on the multimeter body: red or positive, black or negative.
A negative probe is always connected to the connector labeled “ground” or “COM”. The positive one is connected to any other socket.
It should be noted that there can be 2, 3 or 4 connectors. Their number depends on the model and manufacturer. However, even in such multimeters, the socket for connecting only the positive probe can be changed, the negative one remains in the same place.
Tester operating modes
The operation of the multimeter and its modes is regulated using a switch. Its upper vertical position indicates that the device is turned off.
A turn in any other direction indicates a change in mode and is indicated as follows:
All results are displayed on the tester screen in a matter of seconds, reporting the value of the selected indicator with an accuracy of hundredths.
The designation of alternating current on any multimeter can be depicted in the form of AC symbols (alternating current). Accordingly, ACA is alternating current strength, ACV is alternating current voltage. This is a current that changes direction a huge but constant number of times in 1 second. In home networks, the variation frequency is 50 Hz.
Connection sequence
It is important to note that when starting to measure the alternating current level, it is not at all necessary to observe the polarity of connecting the probes. If its value is negative, then a minus sign will simply be displayed on the screen in front of the numbers.
We set the multimeter switch that measures this indicator to the appropriate position and set the measurement range.
The choice of measurement limits should be taken as responsibly as possible. If the measured current significantly exceeds the selected range, this may cause the fuse to blow or, even worse, the entire multimeter.
Pay attention to the choice of connector (socket). Below it should be the maximum current value you want to measure. 10A means that up to 10A of current is measured (quite high).
To regulate the measurement process, first set the switch to the maximum permissible range of values, insert the probe plugs into the sockets. Then, as necessary, reduce the level.
To measure the power of an alternating or direct current, the multimeter must be connected in series with the load (flashlight, lamp, cooler, radio circuit, etc.). This is the basic rule for all electrical measuring instruments. That is, to measure current, the multimeter is connected “into the open” of the circuit.
How to determine the value of alternating voltage in the network
An important point when determining alternating voltage is the fact that the multimeter probes are connected to the device being measured in parallel. This is due to the fact that voltage itself is the potential difference between two points.
You can use the same principle as in the case of alternating current. Adjust the value range from maximum to minimum, not forgetting the position of the probes.
As an example, a standard battery can be used to measure AC voltage. The switch is set to the appropriate mode, the range is set. In this case, the probes touch the battery parallel to each other on both sides. And you can instantly see how the screen displays the voltage value of the element under study.
The situation is the same with constant voltage, but you just need to remember to set the switch to the correct mode.
Regardless of the model and specific operation of the multimeter, it is important to follow the fire safety instructions and handle electrical devices correctly without putting your health at risk.
The basic unit of measurement for electrical voltage is the volt. Depending on the magnitude, voltage can be measured in volts(IN), kilovolts(1 kV = 1000 V), millivolts(1 mV = 0.001 V), microvolts(1 µV = 0.001 mV = 0.000001 V). In practice, most often you have to deal with volts and millivolts.
There are two main types of stress - permanent And variable. Batteries and accumulators serve as a source of constant voltage. The source of alternating voltage can be, for example, the voltage in the electrical network of an apartment or house.
To measure voltage use voltmeter. There are voltmeters switches(analog) and digital.
Today, pointer voltmeters are inferior to digital ones, since the latter are more convenient to use. If, when measuring with a pointer voltmeter, voltage readings have to be calculated on a scale, then digital result measurements are immediately displayed on the indicator. And in terms of dimensions, a pointer instrument is inferior to a digital one.
But this does not mean that pointer instruments are not used at all. There are some processes that cannot be seen with a digital instrument, so switches are more used in industrial enterprises, laboratories, repair shops, etc.
On electric circuit diagrams a voltmeter is indicated by a circle with a capital Latin letter " V" inside. Next to the symbol of the voltmeter its letter designation is indicated “ P.U." and the serial number in the diagram. For example. If there are two voltmeters in the circuit, then next to the first one they write “ PU 1", and about the second " PU 2».
When measuring direct voltage, the diagram indicates the polarity of the voltmeter connection, but if alternating voltage is measured, the polarity of the connection is not indicated.
Voltage is measured between two points schemes: in electronic circuits ah between positive And minus poles, in electrical diagrams between phase And zero. Voltmeter connected parallel to the voltage source or parallel to the chain section- a resistor, lamp or other load on which the voltage needs to be measured:
Let's consider connecting a voltmeter: in the upper diagram, the voltage is measured across the lamp HL1 and simultaneously on the power source GB1. In the diagram below, the voltage is measured across the lamp HL1 and resistor R1.
Before measuring the voltage, determine it view and approximate size. The fact is that the measuring part of voltmeters is designed for only one type of voltage, and this results in different measurement results. A voltmeter for measuring direct voltage does not see alternating voltage, but a voltmeter for alternating voltage, on the contrary, can measure direct voltage, but its readings will not be accurate.
It is also necessary to know the approximate value of the measured voltage, since voltmeters operate in a strictly defined voltage range, and if you make a mistake with the choice of range or value, the device can be damaged. For example. The measurement range of a voltmeter is 0...100 Volts, which means that voltage can only be measured within these limits, since if a voltage is measured above 100 Volts, the device will fail.
In addition to devices that measure only one parameter (voltage, current, resistance, capacitance, frequency), there are multifunctional ones that measure all these parameters in one device. Such a device is called tester(mostly pointer measuring instruments) or digital multimeter.
We won’t dwell on the tester, that’s the topic of another article, but let’s move straight to the digital multimeter. For the most part, multimeters can measure two types of voltage within the range of 0...1000 Volts. For ease of measurement, both voltages are divided into two sectors, and within the sectors into subranges: DC voltage has five subranges, AC voltage has two.
Each subrange has its own maximum measurement limit, which is indicated by a digital value: 200m, 2V, 20V, 200V, 600V. For example. At the “200V” limit, voltage is measured in the range of 0...200 Volts.
Now the measurement process itself.
1. DC voltage measurement.
First we decide on view measured voltage (DC or AC) and move the switch to the desired sector. For example, let's take a AA battery, the constant voltage of which is 1.5 Volts. We select the constant voltage sector, and in it the measurement limit is “2V”, the measurement range of which is 0...2 Volts.
The test leads must be inserted into the sockets as shown in the figure below:
red the dipstick is usually called positive, and it is inserted into the socket, opposite which there are icons of the measured parameters: “VΩmA”;
black the dipstick is called minus or general and it is inserted into the socket opposite which there is a “COM” icon. All measurements are made relative to this probe.
We touch the positive pole of the battery with the positive probe, and the negative pole with the negative one. The measurement result of 1.59 Volts is immediately visible on the multimeter indicator. As you can see, everything is very simple.
Now there's another nuance. If the probes on the battery are swapped, a minus sign will appear in front of the one, indicating that the polarity of the multimeter connection is reversed. The minus sign can be very convenient in the process of setting up electronic circuits, when you need to determine the positive or negative buses on the board.
Well, now let’s consider the option when the voltage value is unknown. We will use a AA battery as a voltage source.
Let’s say we don’t know the battery voltage, and in order not to burn the device, we start measuring from the maximum limit “600V”, which corresponds to the measurement range of 0...600 Volts. Using the multimeter probes, we touch the poles of the battery and on the indicator we see the measurement result equal to “ 001 " These numbers indicate that there is no voltage or its value is too small, or the measurement range is too large.
Let's go lower. We move the switch to the “200V” position, which corresponds to the range of 0...200 Volts, and touch the battery poles with the probes. The indicator showed readings equal to “ 01,5 " In principle, these readings are already enough to say that the voltage of the AA battery is 1.5 Volts.
However, the zero in front suggests going even lower and measuring the voltage more accurately. We go down to the “20V” limit, which corresponds to the range of 0...20 Volts, and take the measurement again. The indicator showed “ 1,58 " Now we can say with certainty that the voltage of a AA battery is 1.58 Volts.
In this way, without knowing the voltage value, they find it, gradually decreasing from a high measurement limit to a low one.
There are also situations when, when taking measurements, the unit "" is displayed in the left corner of the indicator. 1 " A unit indicates that the measured voltage or current is higher than the selected measurement limit. For example. If you measure a voltage of 3 Volts at the “2V” limit, then a unit will appear on the indicator, since the measurement range of this limit is only 0…2 Volts.
There remains one more limit “200m” with a measurement range of 0...200 mV. This limit is intended to measure very small voltages (millivolts), which are sometimes encountered when setting up some amateur radio design.
2. AC voltage measurement.
The process of measuring alternating voltage is no different from measuring direct voltage. The only difference is that for alternating voltage the polarity of the probes is not required.
The AC voltage sector is divided into two subranges 200V And 600V.
At the “200V” limit, you can measure, for example, the output voltage of the secondary windings of step-down transformers, or any other voltage in the range of 0...200 Volts. At the “600V” limit, you can measure voltages of 220 V, 380 V, 440 V or any other voltage in the range of 0...600 Volts.
As an example, let's measure the voltage home network 220 volt.
We move the switch to the “600V” position and insert the multimeter probes into the socket. The measurement result of 229 Volts immediately appeared on the indicator. As you can see, everything is very simple.
And one moment.
Before measuring high voltages, ALWAYS double check that the insulation of the probes and wires of the voltmeter or multimeter is in good condition. and also additionally check the selected measurement limit. And only after all these operations take measurements. This way you will protect yourself and the device from unexpected surprises.
And if anything remains unclear, then watch the video, which shows how to measure voltage and current using a multimeter.