Measurement of basic electrical characteristics. Abstract: Measuring parameters of electrical circuits. Measurements of electrical characteristics of cable, overhead and mixed lines

Measurements of electrical parameters of cable communication lines

1. Measurements of electrical parameters of cable communication lines

The electrical properties of cable communication lines are characterized by transmission parameters and influence parameters.

Transmission parameters evaluate the propagation of electromagnetic energy along a cable chain. Influence parameters characterize the phenomena of energy transfer from one circuit to another and the degree of protection from mutual and external interference.

The transmission parameters include the primary parameters:

R - resistance,

L - inductance,

C - capacity,

G - insulation conductivity and secondary parameters,

Z - wave impedance,

a - attenuation coefficient,

β - phase coefficient.

The influence parameters include primary parameters;

K - electrical connection,

M - magnetic coupling and secondary parameters,

Near-end coupling loss

Bℓ is the far-end coupling loss.

In the low-frequency region, the quality and range of communication are determined mainly by transmission parameters, and when high-frequency circuits are used, the most important characteristics are the influence parameters.

When operating cable communication lines, measurements of their electrical parameters are carried out, which are divided into preventive, control and emergency. Preventive measurements are carried out at certain intervals to assess the condition of communication lines and bring their parameters to standards. Control measurements are carried out after Maintenance and other types of work to assess the quality of their implementation. Emergency measurements are carried out in order to determine the nature and location of damage to the communication line.

1.2 Circuit resistance measurement

There is a distinction between circuit resistance (Rc) to direct current and circuit resistance to alternating current. The DC resistance of 1 km of wire depends on the wire material (resistivity - p), wire diameter and temperature. The resistance of any wire increases with increasing temperature, and decreases with increasing diameter.

For any temperature resistance from 20 °C, the resistance can be calculated using the formula:

Rt =Rt=20 [1+a (t -20) ]Ohm/km ,

where Rt is the resistance at a given temperature,

a is the temperature coefficient of resistance.

For two wire circuits, the resulting resistance value must be multiplied by two.

The resistance of 1 km of wire to alternating current depends, in addition to the above factors, also on the frequency of the current. Resistance to alternating current is always greater than to direct current due to the skin effect.

The dependence of the wire resistance to alternating current on frequency is determined by the formula:

R=K1 × Rt Ohm/km ,

where K1 is a coefficient taking into account the current frequency (with increasing current frequency, K1 increases)

The resistance of the cable circuit and individual wires is measured at the mounted amplification sections. To measure resistance, a DC bridge circuit with a constant balance arm ratio is used. This scheme is provided by measuring instruments PKP-3M, PKP-4M, P-324. Measurement schemes using these instruments are shown in Fig. 1 and fig. 2.

Rice. 1. Scheme for measuring circuit resistance using the PKP device

Rice. 2. Scheme for measuring circuit resistance with the P-324 device

The measured resistance is recalculated per 1 km of circuit and compared with the standards for a given cable. Resistance standards for some types of light and symmetrical cables are given in table. 1.

Table 1

ParameterCableP-274 P-274MP-270TG TBTZB TZGP-296MKB MKGMKSB MKSGSDC circuit resistance ( ¦ = 800Hz), at +20 °C, Ohm/km115 ÷ 12536.0d=0.4 £ 148d=0.8 £ 56.155.5d=1.2 £ 31.9d=0.9 £ 28.5d=0.75 £ 95d=0.9 £ 28.5d=1.4 £ 23.8d=1.2 £ 15.85d=0.6 £ 65.8d=1.0 £ 23.5d=0.7 £ 48d=1.2 £ 16.4d=1.4 £ 11,9

The direct current resistance d is equal, and the active resistance of light field communication cables (P-274, P-274M, P-275) does not depend on the methods of laying lines and weather conditions (“dry”, “damp”) and has only a temperature dependence, increasing with temperature environment(air, soil, etc.).

If, as a result of comparison, the measured resistance value is higher than normal, this may indicate the presence of poor contact in the cable splices or in the connecting halves.

1.3 Capacitance measurement

Capacitance (Cx) is one of the most important primary transmission parameters of cable communication line circuits. By its size, you can judge the condition of the cable and determine the nature and location of its damage.

In actual nature, the cable capacitance is similar to the capacitance of a capacitor, where the role of the plates is played by the surfaces of the wires, and the insulating material located between them (paper, styroflex, etc.) serves as the dielectric.

The capacity of cable communication line circuits depends on the length of the communication line, cable design, insulating materials, and type of twisting.

The capacitance of symmetrical cable circuits is influenced by neighboring cores and cable sheaths, since they are all in close proximity to each other.

Cable capacitance measurements are carried out using measuring instruments such as PKP-3M, PKP-4M, P-324. When measuring the PKP device, the ballistic measurement method is used, and the P-324 device measures using an AC bridge circuit with a variable ratio of the balance arms.

On cable communication lines the following can be carried out:

measuring the capacity of a pair of cores;

measuring core capacitance (relative to ground).

1.3.1 Measuring the capacitance of a pair of cores using the P-324 device

The capacitance of a pair of cores is measured according to the diagram shown in Fig. 3.

Rice. 3. Scheme for measuring the capacitance of a pair of cores

One of the balance arms is a set of nR resistors, three times a resistance store - Rms. The other two arms are the reference capacitance Co and the measured capacitance Cx.

To ensure equality of the shoulder loss angles, the BALANCE Cx ROUGH and BALANCE Cx SMOOTH potentiometers are used. The balance of the bridge is ensured using a resistance store Rms. If the loss angles of the arms and the balance of the bridge are equal, the following equality is valid:

Since Co and R are constant for a given measurement circuit, the measured capacitance is inversely proportional to the magazine resistance. Therefore, the resistance store is calibrated directly in units of capacitance (nF), and the measurement result is determined from the expression:

Cx = n SMS.

1.3.2 Measuring core capacitance relative to ground

Measurement of the conductor capacitance relative to the ground is carried out according to the diagram in Fig. 4.

Rice. 4. Scheme for measuring core capacitance relative to ground

The norms for the average value of the working capacity of a pair of cores for some types of cable communication lines are given in Table. 2.

table 2

ParameterCableP-274 P-274MP-270TG TBTZB TZGP-296MKB MKGMKSB MKSGSAverage value of working capacity, nF/km32.6 ÷ 38.340.45d =0.4 d =0.5 C=50d =0.8 C=3836.0d =1.2 C=27 d =1.4 C=3624.0 ÷ 25d =0.9 С=33.5d =0.6 С=40d =1.0 С=34d =0.7 С=41d =1.2 С=34.5d =1.4 С=35.5

Note:

. The capacity of light field communication cables varies depending on the installation method, weather conditions, and ambient temperature. The greatest influence is exerted by moistening or covering the cable sheath with semiconducting layers (soil, precipitation, soot, etc.) The capacitance of the P-274 cable changes noticeably with increasing temperature and frequency (with increasing temperature the capacitance increases, and with increasing frequency it decreases).

The working capacity of the cable MKSB, MKSG depends on the number of quads (single-, four- and seven-quad) and the number of signal cores.

1.4 Insulation resistance measurement

When assessing the quality of a circuit's insulation, the concept of “insulation resistance” (Riz) is usually used. Insulation resistance is the reciprocal of insulation conductivity.

The conductivity of the circuit insulation depends on the material and condition of the insulation, atmospheric conditions and frequency of the current. The conductivity of the insulation increases significantly when the insulation is contaminated, if there are cracks in it, or if the integrity of the cable insulation layer is damaged. In wet weather, the conductivity of insulation is greater than in dry weather. As the frequency of the current increases, the conductivity of the insulation increases.

Insulation resistance can be measured with PKP-3, PKP-4, P-324 devices during preventive and control tests. Insulation resistance is measured between conductors and between conductor and ground.

To measure the insulation resistance Riz, the control winding of the MU is connected in series with the voltage source and the measured insulation resistance. The smaller the value of the measured Rout, the greater the current in the control winding of the MU, and therefore the greater the EMF in the output winding of the MU. The amplified signal is detected and recorded by the IP device. The instrument scale is calibrated directly in megohms, so the reading of the measured value is Riz. is carried out on the upper or middle scale, taking into account the position of the Rmom LIMIT switch.

When measuring insulation resistance with the PKP device, an ohmmeter circuit is used, which consists of a microammeter and a 220V power source connected in series. The microammeter scale is calibrated from 3 to 1000 MΩ.

Insulation resistance standards for some types of communication cables are given in table. 3.

Table 3

ParameterCableP-274 P-274MP-270TG TBTZB TZGP-296MKB MKGMKSB MKSGSInsulation resistance of single cores relative to other cores, at t=20 °C not less than, MOhm/km 100÷1000 250÷2500 500050001000050001000010000

The insulation resistance of light field communication cables largely depends on the installation method, operating conditions, as well as the ambient temperature.

1.5 Measurement of secondary transmission parameters

1.5.1 Characteristic impedance

Characteristic impedance (Zc) is the resistance that an electromagnetic wave encounters when propagating along a homogeneous circuit without reflection. It is characteristic of this type of cable and depends only on the primary parameters and frequency of the transmitted current. The magnitude of the wave impedance characterizes the circuit, as it shows the relationship between voltage (U) and current ( I ) at any point for a homogeneous chain the value is constant, independent of its length.

Since all primary parameters, with the exception of capacitance, depend on the frequency of the current, as the frequency of the current increases, the characteristic impedance decreases.

Measurement and assessment of the wave resistance value can be carried out using the P5-5 device. For this purpose, work is carried out from both ends of the cable communication line. At one end, the circuit being measured is disrupted by an active resistance, for which it is recommended to use high-frequency mastic resistances SP, SPO or a magazine of non-wire resistances; at the other, the P5-5 device is connected. By adjusting the resistance at the far end of the circuit and increasing the gain of the device at the near end of the circuit, we achieve minimal reflection from the far end of the line according to the P5-5 device. The resistance value selected at the far end of the circuit in this case will correspond to the characteristic impedance of the circuit.

Standards for the average value of wave resistance are given in table. 4.

Table 4

Frequency, kHzCableP-274P-274MP-270TG, TBTZG, TZSP-296MKB MKGMKSB MKSGsukhov watersukhov water0.8720495823585798 ÷1085 368 ÷648 43548749010,0230155258181146231 ÷308 147 ÷200 160190,519616,0205135222158139133 ÷174 15218218660131142 ÷147 130174174,6120129142 ÷146 171168,4200128169,2167,3300126168,2166,3

1.5.2 Operating attenuation

When distributed electrical energy along the wires, the amplitudes of current and voltage decrease or, as they say, undergo attenuation. The decrease in energy over a chain length of 1 km is taken into account through the attenuation coefficient, which is otherwise called kilometer attenuation. The attenuation coefficient is indicated by the letter a and is measured in nepers per 1 km. The attenuation coefficient depends on the primary parameters of the circuit and is caused by two types of losses:

attenuation due to energy losses due to heating of the wire metal;

attenuation due to losses due to insulation imperfections and due to dielectric losses.

In the lower frequency range, losses in the metal dominate, and losses in the dielectric begin to affect them higher.

Since the primary parameters depend on frequency, then a depends on frequency: with increasing current frequency a increases. The increase in attenuation is explained by the fact that with increasing current frequency, the active resistance and conductivity of the insulation increase.

Knowing the circuit attenuation coefficient ( a ) and the length of the chain (ℓ), then we can determine the intrinsic attenuation of the entire chain (a):

a= a × ℓ, Np

For four-way networks that form a communication channel, it is usually not possible to fully ensure the conditions for consistent switching. Therefore, to take into account the inconsistency in both the input and output circuits of the formed communication channel in actual (real) conditions, it is not enough to know only its own attenuation.

Operating attenuation (ap) is the attenuation of the cable circuit under real conditions, i.e. under any loads at its ends.

As a rule, in real conditions the operating attenuation is greater than the intrinsic attenuation (ar >A).

One method for measuring operating attenuation is the level difference method.

When measuring using this method, a generator with a known EMF and a known internal resistance Zо is required. The absolute voltage level at the matched generator load Zо is measured by the station level indicator A and is determined:

and the absolute voltage level at the load Z i measured by station level indicator B.

Standards for the attenuation coefficient of circuits of some types of cable communication lines are presented in table. 5.

Secondary parameters of light field communication cables significantly depend on the method of laying the lines (suspension, on the ground, in the ground, in water).

1.6 Measurement of influence parameters

The degree of influence between the circuits of a cable communication line is usually assessed by the magnitude of the transient attenuation. Transient attenuation characterizes the attenuation of influence currents during their transition from the influencing circuit to the circuit, influenced. When alternating current passes through the influencing circuit, an alternating magnetic field is created around it, which crosses the affected circuit.

A distinction is made between coupling attenuation at the near end Ao and coupling attenuation at the far end Aℓ.

The attenuation of transient currents occurring at the end of the circuit where the influencing circuit generator is located is called near-end transient attenuation.

The attenuation of transient currents arriving at the opposite end of the second circuit is called far-end transient attenuation.

Table 5. Standards for circuit attenuation coefficient, Np/km.

Frequency, kHzCableP-274P-274MP-270TG, TBTZG, TZSP-296MKB MKGMKSB MKSSGsukhov vodesukhov vode0,80,1080,1570,0950,1440,065 0.04÷0.670.043÷0.066 0,0440,043100,2840,3980,2680,3740,1160.344÷0.6440.091÷0.170 0,200,0910,087160,3200,4450,3040,4210,1360.103÷0.1 820,230,0960,092300,1740.129÷0.220 0,240,1110,114600,2290.189÷0.275 0,280,1500,1451200,3110.299÷0.383 0,380,2180,2102000,3920,460,2940,2743000,4740,3720,3325520,81

1.6.1 Near-end coupling loss

Near-end coupling loss is important to measure and evaluate for four-wire systems with in different directions transmission and reception. Such systems include single-cable transmission systems (P-303, P-302, P-301, P-330-6, P-330-24) operating over a single-four cable (P-296, P-270).

The most common method for measuring transient attenuation is the comparison method used when using a set of instruments VIZ-600, P-322. When measuring with the P-324 device, a mixed (comparison and addition) method is used.

The essence of the comparison and addition method is that in position 2 the value of the transient attenuation (Ao) is supplemented by the magazine attenuation (amz) to a value of less than 10 Np. By changing the magazine attenuation, the condition Ao + amz ≥10 Np is achieved.

For the convenience of reading the measured value, the numbers on the NP switch are not the attenuation of the amz, which is actually introduced by the store, but the difference of 10 - amz.

Since the magazine attenuation does not change smoothly, but in steps of 1 Np, the remainder of the attenuation in Np is measured on a pointer scale (PI) ranging from 0 to 1 Np.

Before the measurement, the instrument (IP) is calibrated, for which the NP circuit switch is set to the GRAD position (position 1 in Fig. 9). In this case, the output of the generator is connected to the meter through a reference extension cable (EC) with an attenuation of 10 Np.

The standards for transient attenuation are given in table. 6.

Table 6. Standards for transient attenuation at the near end within and between adjacent quadruples, not less, Np

Cable type Frequency, kHz Line length, km Crosstalk attenuation P-27060106.0 P-29660108.8 MKB MKG100 2000.850 0.8506.8 6.8 MKSB, MKSG Entire frequency range 0.6507.2

For the P-296 cable, crosstalk attenuation is also checked at frequencies of 10 kHz and 30 kHz.

1.6.2 Far-end crosstalk

Far-end crosstalk is important to measure and evaluate also for four-wire systems, but with the same receive and transmit directions. Such systems include two-cable transmission systems such as P-300, P-330-60.

To measure the transition attenuation at the far end of Aℓ, it is necessary to have two P-324 devices installed at opposite ends of the measured circuits. The measurement is carried out in three stages.

Also, using the P-324 device, it is possible to measure attenuations of at least 5 Np; at the input of the device, an extension cord UD 5 Np, which is part of the device, is turned on to check the functionality of the device.

The resulting measurement result is divided in half and the attenuation of one circuit is determined.

After this, the circuit is assembled and the measuring path of the station B device connected to the influencing circuit is calibrated. In this case, the sum of the attenuation of the circuit, the UD 5Np extension cord and the attenuation magazine must be at least 10 Np, the remainder of the attenuation in excess of 10 Np is set on the pointer device.

In the third step, the coupling attenuation at the far end is measured. The measurement result is the sum of the readings of the NP switch and the pointer device.

The measured value of the far-end coupling attenuation is compared with the norm. The norm of transient attenuation at the far end is given in table. 7.

Table 7

Cable type Frequency, kHz Line length, km Transition attenuation P-27060105.5 P-29660105.0 MKB MKG100 2000.850 0.8507.8 7.8 MKSB, MKSG Entire frequency range 0.6508.2

In all symmetrical cable circuits, the transient attenuation decreases with increasing frequency approximately according to a logarithmic law. To increase the transient attenuation between circuits, during manufacturing, conductive cores are twisted into groups (pairs, fours, eights), the groups are twisted into a cable core, the circuits are shielded, and when laying cable communication lines, the cable is balanced. Balancing on low-frequency cables consists of additionally crossing them during deployment and turning on capacitors. Balancing on HF cables is the crossing and inclusion of counter-coupling circuits. The need for balancing may arise when the influence parameters of the cable deteriorate during its long-term use or during the construction of a long-distance communication line. The need to balance the cable must be determined in each specific case, based on the actual value of the transient attenuation of the circuits, which depends on the communication system (the system of using cable circuits and compaction equipment) and the length of the line.

2. Determination of the nature and location of damage to cable communication lines

2.1 General provisions

Communication cables may have the following types damage:

lowering the insulation resistance between cable cores or between cores and ground;

lowering the insulation resistance “shell - ground” or “armor - ground”;

complete cable break;

dielectric breakdown;

asymmetry of core resistance;

broken pairs in a balanced cable.

2.2 Tests to determine the nature of damage

Determining the nature of the damage (“ground”, “break”, “short” decrease in insulation resistance) is carried out by testing each cable core using megger or ohmmeter circuits of various measuring instruments (for example, P-324, PKP-3, PKP-4, KM- 61C, etc.). A combined “tester” device can be used as an ohmmeter.

Tests are carried out in the following order:

The insulation resistance between one core and the others connected to the grounded screen is checked.

At station A, where the tests are carried out, all the cores except one are connected together and to the screen and grounded. At station B, the conductors are insulated. The insulation resistance is measured and compared with the standard for a given cable type. Tests and analysis are carried out for each cable core. If the measured insulation resistance value is below the norm, then the nature of the damage is determined:

damage to insulation relative to ground;

damage to the insulation relative to the cable screen;

damage to the insulation relative to other cable cores.

To determine the nature of the damage at station A, they alternately remove the “ground” from the cable cores and carry out an analysis:

a) if removing the “ground” from some core (for example, from core 2 in Fig. 13) leads to sharp increase insulation resistance, then the insulation between the tested core (core 1) and the one from which the “ground” is removed (core 2) is damaged;

b) if removing the “ground” from all cores does not lead to an increase in insulation resistance to the norm, then the insulation of the tested core (core 1) is damaged relative to the cable shield (ground).

If during the next test it turns out that the insulation resistance is hundreds of Ohms or units of kOhms, then this indicates a possible short circuit between the cable cores being tested (for example, a “short” is shown between cores 3 and 4);

The integrity of the cable cores is checked, for which all the cores at station B are connected together and to the screen. At station A, each core is checked for integrity with an ohmmeter.

Establishing the nature of the damage allows you to choose one of the methods for determining the location of the damage.

2.3 Determining the location of damage to the insulation of wire cores

To determine the location of damage to the core insulation, bridge circuits are used, the choice of which depends on whether a given cable has serviceable cores or not.

If there is a serviceable wire equal in resistance to the damaged one, and if the insulation resistance of the damaged wire is up to 10 mOhm, measurements are made using the bridge method with a variable ratio of the balanced arms.

During measurements, the resistance values of the bridge arms Ra and Rm are selected in such a way that there is no current in the diagonal of the bridge into which the power supply is connected.

When determining the location of insulation damage using the bridge method with a variable balance arm ratio, PKP-3, PKP-4, KM-61S devices are used. In these devices, the resistance Rm is variable and is determined by measurements at the moment of equilibrium of the bridge, and the resistance Ra is constant and for PKP devices is chosen equal to 990 Ohms, for the KM-61S device - 1000 Ohms.

If the good and damaged wires have different resistances, then measurements are taken from both ends of the cable communication line.

When using PKP-3, PKP-4 devices, other methods of measuring insulation resistance can be used to determine the location of cable damage:

Bridge method with variable balance arm ratio with auxiliary line. It is used when there are serviceable wires that are not equal in resistance to the damaged one, and the insulation resistance of the damaged wire is up to 10 MOhm, and the auxiliary wire is over 5000 MOhm,
Bridge method with constant balance arm ratio using double loop method. It is used in the presence of significant interference currents and insulation resistance of the damaged wire up to 10 M0 m, and auxiliary - over 5000 MOhm.
Bridge method with a constant balance arm ratio at high transient resistances. It is used when there is a serviceable wire equal in resistance to the damaged one, and a transition resistance at the site of insulation damage of up to 10 MOhm.
Method of two-way measurements of loop resistance of damaged wires. It is used in the absence of serviceable wires and the transition resistance is on the order of the resistance of the loop.

5. Method idle move and short circuit when using a bridge with a constant balance arm ratio. It is used in the absence of serviceable wires and the transition resistance at the site of insulation damage is up to 10 kOhm.

No-load and short-circuit method when using a bridge with a variable balance arm ratio. It is used in the absence of serviceable wires and the transition resistance at the site of insulation damage is from 0.1 to 10 MOhm.

In the absence of serviceable wires, determining the location of insulation damage using bridge methods with sufficient accuracy presents certain difficulties. In this case, pulse and inductive methods can be used. For measurements using the pulse method, they use the P5-5, P5-10 devices, the range of which can reach 20-25 km on symmetrical communication cables.

2.4 Determining the location of broken wires

Determining the location of a wire break can be done using the following methods:

Pulsed current bridge method. It is used when there is a working wire that is equal in resistance to the damaged one.

Capacity comparison method (ballistic method). It is used when the specific capacitance of the good and damaged wires is equal.

Method for comparing capacitances with two-sided measurements. It is used when the specific capacitance of the damaged and serviceable wires is unequal and, in particular, when it is impossible to ground the unmetered wires of the line.

To determine the location of a wire break, PKP-3, PKP-4, KM-61C, P-324 devices can be used.

If there is a serviceable core in the cable and it is possible to ground all other cable cores, the working capacitance of the serviceable core (Cℓ), then the damaged core (Cx) is measured one by one.

If, due to the operating conditions of the cable, grounding of the remaining unmeasured conductors is impossible, then to obtain a reliable result, the broken conductor is measured on both sides, and the distance to the break point is calculated using the formula:

Objects electrical measurements are all electrical and magnetic quantities: current, voltage, power, energy, magnetic flux, etc. Determining the values of these quantities is necessary to assess the operation of all electrical devices, which determines the exceptional importance of measurements in electrical engineering.

Electrical measuring devices are also widely used to measure non-electrical quantities (temperature, pressure, etc.), which for this purpose are converted into proportions to them. electrical quantities. Such measurement methods are known collectively as electrical measurements of non-electrical quantities. The use of electrical measurement methods makes it possible to relatively easily transmit instrument readings over long distances (telemetering), control machines and devices (automatic control), automatically perform mathematical operations on measured quantities, simply record (for example, on tape) the progress of controlled processes, etc. Thus, electrical measurements are necessary when automating a wide variety of production processes.

In the Soviet Union, the development of electrical instrument manufacturing proceeds in parallel with the development of electrification of the country and especially rapidly after the Great Patriotic War. The high quality of the equipment and the required accuracy of the measuring instruments in use are guaranteed by state supervision of all measures and measuring instruments.

12.2 Measures, measuring instruments and measurement methods

The measurement of any physical quantity consists of comparing it through a physical experiment with the value of the corresponding physical quantity taken as a unit. In the general case, for such a comparison of the measured quantity with a measure - a real reproduction of a unit of measurement - you need comparison device. For example, a standard resistance coil is used as a measure of resistance together with a comparison device - a measuring bridge.

The measurement is greatly simplified if there is direct reading device(also called an indicating instrument), showing the numerical value of a measured quantity directly on a scale or dial. Examples include ammeter, voltmeter, wattmeter, electric energy meter. When measuring with such a device, a measure (for example, a standard resistance coil) is not needed, but a measure was needed when calibrating the scale of this device. As a rule, comparison instruments have higher accuracy and sensitivity, but measurement with direct reading instruments is simpler, faster and cheaper.

Depending on how the measurement results are obtained, measurements are distinguished between direct, indirect and cumulative.

If the measurement result directly gives the desired value of the quantity being studied, then such a measurement is one of the direct ones, for example, measuring current with an ammeter.

If the measured quantity has to be determined on the basis of direct measurements of other physical quantities with which the measured quantity is related by a certain relationship, then the measurement is classified as indirect. For example, an indirect measurement will be the resistance of an element of an electrical circuit when measuring voltage with a voltmeter and current with an ammeter.

It should be borne in mind that with indirect measurement, a significant decrease in accuracy is possible compared to the accuracy with direct measurement due to the addition of errors in direct measurements of quantities included in the calculation equations.

In a number of cases, the final measurement result was derived from the results of several groups of direct or indirect measurements of individual quantities, and the value under study depends on the measured quantities. This measurement is called cumulative. For example, cumulative measurements include determining the temperature coefficient of electrical resistance of a material based on measurements of the material's resistance at various temperatures. Cumulative measurements are typical for laboratory studies.

Depending on the method of using instruments and measures, it is customary to distinguish the following main measurement methods: direct measurement, zero and differential.

When using direct measurement method(or direct reading) the measured quantity is determined by

direct reading of the reading of a measuring device or direct comparison with a measure of a given physical quantity (measuring current with an ammeter, measuring length with a meter). In this case, the upper limit of measurement accuracy is the accuracy of the measuring indicating device, which cannot be very high.

When measuring zero method an exemplary (known) quantity (or the effect of its action) is adjusted and its value is brought to equality with the value of the measured quantity (or the effect of its action). Using a measuring device in this case only achieves equality. The device must be of high sensitivity, and it is called zero device or null indicator. Magnetoelectric galvanometers are usually used as zero devices for direct current (see § 12.7), and for alternating current - electronic null indicators. The measurement accuracy of the zero method is very high and is mainly determined by the accuracy of the reference measures and the sensitivity of the zero instruments. Among the zero-point electrical measurement methods, the most important are bridge and compensation methods.

Even greater accuracy can be achieved with differential methods measurements. In these cases, the measured quantity is balanced by a known quantity, but the measuring circuit is not brought to complete equilibrium, and the difference between the measured and known quantities is measured by direct reading. Differential methods are used to compare two quantities whose values differ little from one another.

Plan

Introduction

Current meters

Voltage measurement

Combined devices of the magnetoelectric system

Universal electronic measuring instruments

Measuring shunts

Instruments for measuring resistance

Determination of ground resistance

Magnetic flux

Induction

Bibliography

Introduction

Measurement is the process of finding the value of a physical quantity experimentally, using special technical means– measuring instruments.

So measurement is information process obtaining experimentally a numerical relationship between a given physical quantity and some of its values taken as a unit of comparison.

The result of a measurement is a named number found by measuring a physical quantity. One of the main tasks of measurement is to assess the degree of approximation or difference between the true and actual values of the measured physical quantity - measurement error.

The main parameters of electrical circuits are: current, voltage, resistance, current power. Electrical measuring instruments are used to measure these parameters.

Measuring the parameters of electrical circuits is carried out in two ways: the first is a direct measurement method, the second is an indirect measurement method.

The direct measurement method involves obtaining the result directly from experience. An indirect measurement is a measurement in which the desired quantity is found on the basis of a known relationship between this quantity and the quantity obtained as a result of direct measurement.

Electrical measuring instruments are a class of devices used to measure various electrical quantities. The group of electrical measuring instruments also includes, in addition to the measuring instruments themselves, other measuring instruments - gauges, converters, complex installations.

Electrical measuring instruments are classified as follows: according to measured and reproducible physical quantity(ammeter, voltmeter, ohmmeter, frequency meter, etc.); by purpose (measuring instruments, measures, measuring transducers, measuring installations and systems, auxiliary devices); by the method of providing measurement results (displaying and recording); by measurement method (direct assessment devices and comparison devices); by method of application and design (panel, portable and stationary); according to the operating principle (electromechanical - magnetoelectric, electromagnetic, electrodynamic, electrostatic, ferrodynamic, induction, magnetodynamic; electronic; thermoelectric; electrochemical).

In this essay I will try to talk about the device, the principle of operation, give a description and brief description electrical measuring instruments of electromechanical class.

Current measurement

Ammeter is a device for measuring current in amperes (Fig. 1). The scale of ammeters is calibrated in microamperes, milliamperes, amperes or kiloamperes in accordance with the measurement limits of the device. In an electrical circuit, the ammeter is connected in series with the section of the electrical circuit (Fig. 2) in which the current is measured; to increase the measurement limit - with a shunt or through a transformer.

The most common ammeters are those in which the moving part of the device with the pointer rotates through an angle, proportional to the magnitude measured current.

Ammeters are magnetoelectric, electromagnetic, electrodynamic, thermal, induction, detector, thermoelectric and photoelectric.

Magnetoelectric ammeters measure direct current; induction and detector - alternating current; ammeters of other systems measure the strength of any current. The most accurate and sensitive are magnetoelectric and electrodynamic ammeters.

The principle of operation of a magnetoelectric device is based on the creation of torque due to the interaction between the field of a permanent magnet and the current that passes through the winding of the frame. An arrow is connected to the frame, which moves along the scale. The angle of rotation of the arrow is proportional to the current strength.

Electrodynamic ammeters consist of fixed and moving coils connected in parallel or in series. The interaction between the currents that pass through the coils causes deflections of the moving coil and the arrow connected to it. In an electrical circuit, the ammeter is connected in series with the load, and at high voltages or high currents - through a transformer.

Technical data of some types of domestic ammeters, milliammeters, microammeters, magnetoelectric, electromagnetic, electrodynamic, and thermal systems are given in Table 1.

Table 1. Ammeters, milliammeters, microammeters

Instrument system	Device type	Accuracy class	Measurement limits
Magnetoelectric	M109	0,5	1; 2; 5; 10 A
	M109/1	0,5	1.5-3 A
	М45М	1,0	75mV
	М45М	1,0	75-0-75mV
	M1-9	0,5	10-1000 µA
	M109	0,5	2; 10; 50 mA
	200 mA
	М45М	1,0	1.5-150 mA
Electromagnetic	E514/3	0,5	5-10 A
	E514/2	0,5	2.5-5 A
	E514/1	0,5	1-2 A
	E316	1,0	1-2 A
	3316	1,0	2.5-5 A
	E513/4	1,0	0.25-0.5-1 A
	E513/3	0,5	50-100-200 mA
	E513/2	0,5	25-50-100 mA
	E513/1	0,5	10-20-40 mA
	E316	1,0	10-20 mA
Electrodynamic	D510/1	0,5	0.1-0.2-0.5-1-2-5 A
Thermal	E15	1,0	30;50;100;300 mA

Voltage measurement

Voltmeter - measuring device direct reading to determine voltage or EMF in electrical circuits (Fig. 3). Connected in parallel to the load or source of electrical energy (Fig. 4).

According to the operating principle, voltmeters are divided into: electromechanical - magnetoelectric, electromagnetic, electrodynamic, electrostatic, rectifier, thermoelectric; electronic - analog and digital. By purpose: direct current; alternating current; pulse; phase sensitive; selective; universal. By design and method of application: panel; portable; stationary. Technical data of some domestic voltmeters, millivoltmeters of magnetoelectric, electrodynamic, electromagnetic, and thermal systems are presented in Table 2.

Table 2. Voltmeters and millivoltmeters

Instrument system	Device type	Accuracy class	Measurement limits
Electrodynamic	D121	0,5	150-250 V
D567	0,5	15-600 V
Magnetoelectric	M109	0,5	3-600 V
M250	0,5	3; 50; 200; 400 V
М45М	1,0	75 mV;
75-0-75 mV
75-15-750-1500 mV
M109	0,5	10-3000 mV
Electrostatic	C50/1	1,0	30 V
C50/5	1,0	600 V
C50/8	1,0	3 kV
S96	1,5	7.5-15-30 kV
Electromagnetic	E515/3	0,5	75-600 V
E515/2	0,5	7.5-60 V
E512/1	0,5	1.5-15 V
With electronic converter	F534	0,5	0.3-300 V
Thermal	E16	1,5	0.75-50 V

For measurements in direct current circuits, combined instruments of the magnetoelectric system, ampere-voltmeters, are used. Technical data on some types of devices are given in Table 3.

Table 3. Combined devices of the magnetoelectric system .

Name	Type	Accuracy class	Measurement limits
Millivolt-milliammeter	M82	0,5	15-3000 mV; 0.15-60 mA
Voltammeter	M128	0,5	75mV-600V; 5; 10; 20 A
Ampere-voltmeter	M231	1,5	75-0-75 mV; 100-0-100 V; 0.005-0-0.005 A; 10-0-10 A
Voltammeter	M253	0,5	15mV-600V; 0.75 mA-3 A
Millivolt-milliammeter	M254	0,5	0.15-60 mA; 15-3000 mV
Microamperevoltmeter	M1201	0,5	3-750 V; 0.3-750 µA
Voltammeter	M1107	0,2	45mV-600V; 0.075 mA-30 A
Milliamp-voltmeter	М45М	1	7.5-150 V; 1.5 mA
Volt-ohmmeter	M491	2,5	3-30-300-600 V; 30-300-3000 kOhm
Ampere-voltmeter	M493	2,5	3-300 mA; 3-600 V; 3-300 kOhm
Ampere-voltmeter	M351	1	75mV-1500V; 15 µA-3000 mA; 200 Ohm-200 Mohm

Technical data on combined instruments - ampere-voltmeters and ampere-voltmeters for measuring voltage and current, as well as power in alternating current circuits.

Combined portable instruments for measuring direct and alternating current circuits provide measurement of direct and alternating currents and resistances, and some also provide element capacitance in a very wide range, are compact, and have self-powered power, which ensures their wide application. The accuracy class of this type of devices is DC 2.5; on variable – 4.0.

Universal electronic measuring instruments

Universal measuring instruments (universal voltmeters) are widely used for measuring electrical quantities. These devices, as a rule, make it possible to measure alternating and direct voltages and currents, resistance, and, in some cases, signal frequency over an extremely wide range. In the literature, they are often called universal voltmeters, due to the fact that any value measured by the devices is somehow converted into voltage and amplified by a broadband amplifier. The devices have a dial scale (an electromechanical type device) or a display with a liquid crystal indicator; some devices have built-in programs that provide mathematical processing of the results.

Information about some types of modern domestic universal devices is given in Table 4.

Table 4. Universal measuring instruments

Device type	Limits of measured values, additional functions	additional information
V7-21A	1 µV-1,000 V, 0.01 Ohm-12 Mohm, frequency up to 20 kHz	weight 5.5 kg
V7-34A	1 µV-1,000 V, 1 mOhm - 10 Mohm, error 0.02%	weight 10 kg
B7-35	0.1mV-1000V, 0.1 µV-10 A, 1 Ohm-10 MOhm,	battery powered weight 2 kg
V7-36	0.1 mV-1,000 V, 1 Ohm-10 MOhm,	Pointer, battery powered

Accessories included with universal devices:

1. AC voltage probe in the range of 50KHz-1GHz for AC voltage extension with all universal voltmeters and multimeters.

2. High-voltage DC voltage divider up to 30 kV 1: 1000. Table 5 shows the technical data of the universal B3-38V.

Table 5. Technical data of digital millivoltmeter V3-38V

Characteristics	Options	Meaning
AC voltage	Voltage range Measurement limit	10 µV…300 V 1 mV/… /300 V (12 p/ranges, step 1-3)
	Frequency range	Normal area: 45 Hz…1 MHz Workspaces: 20 Hz…45 Hz; 1 MHz-3 MHz; 3 MHz-5 MHz
	Measurement error Additional error Settling time	±2% (for harmonic vibrations) ±1/3xKg, at Kg 20% (for non-harmonic vibrations)
	Maximum input voltage Input impedance	600 V (250 V DC) 4 MOhm/25 pF within 1 mV/…/300 mV 5 MOhm/15pF within 1 V/…/300 V
Voltage transformer	Output voltage Conversion error Output impedance
Wideband amplifier	Maximum output voltage	(100±20) mV
Display	Type of indicators Display format	LCD indicator 3 ½ digits
Total information	Supply voltage Dimensional data	220V±10%, 50Hz 155x209x278 mm

Universal voltmeters with liquid crystal display of the results of measuring direct and alternating currents and voltages, resistance in a 2/4 wire circuit, frequencies and periods, measurement of the rms value of alternating current and arbitrary voltage.

In addition, if there are replaceable temperature sensors, the devices provide temperature measurement from -200 to +1110 0 C, power measurement, relative levels (dB), recording/reading up to 200 measurement results, automatic or manual selection measurement limits, built-in test control program, musical sound control.

Measuring shunts

Shunts are designed to expand the limits of current measurement. A shunt is a calibrated, usually flat, conductor (resistor) of a special design made of manganin, through which the measured current passes. The voltage drop across the shunt is a linear function of the current. The rated voltage corresponds to the rated current of the shunt. They are mainly used in DC circuits in combination with magnetoelectric measuring instruments. When measuring small currents (up to 30 A), shunts are built into the device body. When measuring high currents (up to 7500 A), external shunts are used. Shunts are divided into accuracy classes: 0.02; 0.05; 0.1; 0.2 and 0.5.

To expand the measurement limits of voltage devices, calibrated resistors, called additional resistances, are used. Additional resistors are made of manganin insulated wire and are also divided into accuracy classes. Information about shunts is presented in Table 6.

Table 6. Measuring shunts

Type	Rated current, A	Nominal voltage drop, mV	Accuracy class
P114/1	75	45	0,1
P114/1	150	45	0,1
P114/1	300	45	0,1
75RI	0,3-0,75	75	0,2
75RI	1,5-7,5	75	0,2
75RI	15-30	75	0,2
75RI	75	75	0,2
75ShS-0.2	300; 500; 750; 1000; 1500; 2000; 4000	75	0,2
75ShS	5; 10; 20; 30; 50	75	0,5
75ShSM	75; 100; 150; 200; 300; 500; 750; 1 000	75	0,5

Instruments for measuring resistance

Devices for measuring electrical resistance, depending on the range of resistance measured by the devices, are called ohmmeters, microohmmeters, magaohmmeters. To measure the resistance to current spreading of grounding devices, grounding meters are used. Information about some types of these devices is given in Table 7.

Table 7. Ohmmeters, microohmmeters, megaohmmeters, grounding meters

Device	Type	Measurement limits	Basic error or accuracy class
Ohmmeter	M218	0.1-1-10-100 Ohm 0.1-1-10-100 kOhm 0.1-1-10-100 MOhm	1,5-2,5%
Ohmmeter	M371	100-10,000 kOhm;	±1.5%
Ohmmeter	M57D	0-1 500 Ohm	±2.5%
Microohmmeter	M246	100-1,000 µOhm 10-100 mOhm-10 Ohm
Microohmmeter	F415	100-1,000 µOhm;	-
Megaohmmeter	M4101/5		1
Megaohmmeter	M503M		1
Megaohmmeter	M4101/1		1
Megaohmmeter	M4101/3		1

Determination of ground resistance

The term grounding means electrical connection any circuit or equipment to ground. Grounding is used to set and maintain the potential of a connected circuit or equipment as close to ground potential as possible. The ground circuit is formed by the conductor, the clamp by which the conductor is connected to the electrode, the electrode, and the ground around the electrode. Grounding is widely used for electrical protection purposes. For example, in lighting equipment, grounding is used to short-circuit fault current to ground to protect personnel and equipment components from high voltage exposure. The low resistance of the grounding circuit ensures that the breakdown current flows to the ground and prompt operation of the protective relays. As a result, extraneous voltage is removed as quickly as possible to avoid exposing personnel and equipment to it. To the best way fix the reference potential of the equipment in order to protect it from static electricity and limit voltages on the equipment frame to protect personnel, the ideal ground circuit resistance should be zero.

PRINCIPLE OF GROUNDING RESISTANCE MEASUREMENT

A voltmeter measures the voltage between pins X and Y and an ammeter - the current flowing between pins X and Z (Fig. 5)

notice, that points X,Y and Z correspond points X,P and C of a device operating on a 3-point circuit or points C1, P2 and C2 of a device operating on a 4-point circuit.

Using the formulas of Ohm's law E = R I or R = E / I, we can determine the grounding resistance of the electrode R. For example, if E = 20 V and I = 1 A, then:

R = E / I = 20 / 1 = 20 Ohm

If you use a grounding tester, you will not need to make these calculations. The device itself will generate the current necessary for the measurement and directly display the value of the grounding resistance.

For example, consider a meter from a foreign manufacturer, brand 1820 ER (Fig. 6 and Table 8).

Table 8. Type 1820 Meter Specifications ER

Characteristics	Options	Values
Ground resistance	Measurement limits	20; 200; 2000 Ohm
	Permission	0.01 Ohm at 20 Ohm limit 0.1 Ohm at 200 Ohm limit 1 ohm at 2,000 ohm limit
	Measurement error	±(2.0%+2 digit units)
	Test signal	820 Hz, 2 mA
Touch voltage	Measurement limits	200 V, 50…60 Hz
	Permission	1 V
	Measurement error	±(1%+2 digit units)
Total information	Indicator	LCD, maximum displayed number 2,000
	Supply voltage	1.5 V x 8 (type AA)
	dimensions	170 x 165 x 92 mm
	Weight	1 kg

Magnetic flux

General information.

Magnetic flux- flux as an integral of the magnetic induction vector through a finite surface. Determined through the surface integral

in this case the vector element of the surface area is defined as

where is the unit vector normal to the surface.

where α is the angle between the magnetic induction vector and the normal to the area plane.

Magnetic flux through a circuit can also be expressed in terms of the circulation of the vector potential magnetic field along this circuit:

Units

In the SI system, the unit of magnetic flux is weber (Wb, dimension - V s = kg m² s −2 A −1), in the CGS system it is maxwell (Mks); 1 Wb = 10 8 μs.

A device for measuring magnetic fluxes is called Fluxmeter(from Latin fluxus - flow and ... meter) or webermeter.

Induction

Magnetic induction- vector quantity, which is the force characteristic of the magnetic field at a given point in space. Shows the force with which a magnetic field acts on a charge moving at a speed.

More precisely, it is such a vector that the Lorentz force acting on a charge moving with speed is equal to

where α is the angle between the velocity and magnetic induction vectors.

Also, magnetic induction can be defined as the ratio of the maximum mechanical torque forces acting on a frame with current placed in a uniform field, to the product of the current strength in the frame and its area.

It is the main characteristic of a magnetic field, similar to the vector of electric field strength.

In the CGS system, magnetic field induction is measured in gauss (G), in the SI system - in tesla (T)

1 T = 10 4 G

Magnetometers used to measure magnetic induction are called teslameters.

Bibliography

1. Handbook of electrical engineering and electrical equipment, Aliev I.I.

2. Electrical engineering, Ryabov V.I.

3. Modern measuring electrical equipment, Zhuravlev A.

Measurement is the process of finding experimentally the value of a physical quantity using special technical means. Electrical measuring instruments are widely used in monitoring the operation of electrical installations, in monitoring their condition and operating modes, in taking into account the consumption and quality of electrical energy, in the repair and adjustment of electrical equipment.

Electrical measuring instruments are electrical measuring instruments designed to generate signals that are functionally related to the measured physical quantities in a form understandable to an observer or an automatic device.

Electrical measuring instruments are divided into:

by the type of information received on instruments for measuring electrical (current, voltage, power, etc.) and non-electrical (temperature, pressure, etc.) quantities;
according to the measurement method - for direct assessment devices (ammeter, voltmeter, etc.) and comparison devices (measuring bridges and compensators);
according to the method of presenting measured information - analog and discrete (digital).

The most widely used analog devices for direct assessment are classified according to the following criteria: type of current (direct or alternating), type of measured quantity (current, voltage, power, phase shift), principle of operation (magnetoelectric, electromagnetic, electro- and ferrodynamic), accuracy class and operating conditions.

To expand the measurement limits electrical appliances for direct current, shunts (for current) and additional resistances Rd (for voltage) are used; on alternating current, current transformers (tt) and voltage transformers (tn).

Instruments used to measure electrical quantities.

Voltage measurement is carried out with a voltmeter (V), connected directly to the terminals of the section of the electrical circuit under study.

Current measurement is carried out with an ammeter (A), connected in series with the elements of the circuit under study.

Measurement of power (W) and phase shift () in alternating current circuits is carried out using a wattmeter and a phase meter. These devices have two windings: a fixed current winding, which is connected in series, and a moving voltage winding, connected in parallel.

Frequency meters are used to measure alternating current frequency (f).

To measure and account for electrical energy - electrical energy meters connected to the measuring circuit similarly to wattmeters.

The main characteristics of electrical measuring instruments are: accuracy, reading variations, sensitivity, power consumption, reading settling time and reliability.

The main parts of electromechanical devices are the electrical measuring circuit and the measuring mechanism.

The measuring circuit of the device is a converter and consists of various connections of active and reactive resistance and other elements, depending on the nature of the conversion. The measuring mechanism converts electromagnetic energy into mechanical energy necessary for the angular movement of its moving part relative to the stationary one. The angular movements of the pointer a are functionally related to the torque and counteracting moment of the device by a transformation equation of the form:

k is the design constant of the device;

Electrical quantity under the influence of which the arrow of the device deviates by an angle

Based on this equation, it can be argued that if:

input quantity X to the first power (n=1), then a will change sign when the polarity changes, and the device cannot operate at frequencies other than 0;
n=2, then the device can operate on both direct and alternating current;
the equation includes more than one quantity, then you can choose any one as the input, leaving the rest constant;
two quantities are input, then the device can be used as a multiplying converter (wattmeter, counter) or dividing converter (phase meter, frequency meter);
with two or more input values on a non-sinusoidal current, the device has the property of selectivity in the sense that the deviation of the moving part is determined by the value of only one frequency.

Common elements are: a reading device, a moving part of the measuring mechanism, devices for creating torque, counteracting and calming moments.

The reading device has a scale and a pointer. The interval between adjacent scale marks is called a division.

The instrument division value is the value of the measured quantity that causes the instrument needle to deflect by one division and is determined by the dependencies:

Scales can be uniform or uneven. The area between the initial and final values of the scale is called the range of instrument readings.

The readings of electrical measuring instruments differ somewhat from the actual values of the measured quantities. This is caused by friction in the measuring part of the mechanism, the influence of external magnetic and electric fields, changes in ambient temperature, etc. The difference between the measured Ai and actual Ad values of the controlled quantity is called the absolute measurement error:

Since the absolute error does not give an idea of the degree of measurement accuracy, the relative error is used:

Since the actual value of the measured quantity during measurement is unknown, the accuracy class of the device can be used to determine it.

Ammeters, voltmeters and wattmeters are divided into 8 accuracy classes: 0.05; 0.1; 0.2; 0.5; 1.0; 1.5; 2.5; 4.0. The number indicating the accuracy class determines the largest positive or negative basic reduced error that a given device has. For example, for an accuracy class of 0.5, the given error will be ±0.5%.

Specifications ammeters

Parameter name	Ammeters E47	Voltmeters E47
System	electromagnetic	electromagnetic
Information output method	analog	analog
Measuring range	0...3000 A	0...600 V
Installation method	on the shield panel	on the shield panel
Switching method	<50 А- непосредственный, >100 A - via current transformer with 5 A secondary current	direct
Accuracy class	1,5	1,5
Limit of permissible basic error of instruments, %	±1.5	±1.5
Rated operating voltage, no more	400 V	600 V
Permissible long-term overload (no more than 2 hours)		120% of the final value of the measuring range
Average time to failure, not less, h	65000	65000
Average term service, at least, years	8	8
Ambient air temperature, °C	20±5	20±5
Frequency of the measured value, Hz	45...65	45...65
Mounting plane position	vertical	vertical
Dimensions, mm	72x72x73.5 96x96x73.5	72x72x73.5 96x96x73.5

Electrical measuring instruments (ammeters and voltmeters) series E47

Used in low-voltage complete devices in distribution electrical networks residential, commercial and industrial facilities.

E47 ammeters - analog electromagnetic electrical measuring instruments - are designed to measure current in AC electrical circuits.

E47 voltmeters - analog electromagnetic electrical measuring instruments - are designed to measure voltage in alternating current electrical circuits.

Wide measurement range: ammeters up to 3000 A, voltmeters up to 600 V. Accuracy class 1.5.

Ammeters designed to measure currents above 50 A are connected to the circuit being measured via a current transformer with a rated secondary operating current of 5 A.

Operating principle of ammeters and voltmeters of the E47 series

Ammeters and voltmeters E47 are devices with electromagnetic system. They consist of a round coil with movable and stationary cores placed inside. When current flows through the turns of the coil, a magnetic field is created that magnetizes both cores. As a result.

the like poles of the cores repel each other, and the movable core turns the axis with the arrow. To protect against negative influence external magnetic fields, the coil and cores are protected by a metal shield.

The principle of operation of magnetoelectric system devices is based on the interaction of the field of a permanent magnet and conductors with current, and the electromagnetic system is based on the retraction of a steel core into a stationary coil when there is current in it. The electrodynamic system has two coils. One of the coils, movable, is mounted on an axis and is located inside the stationary coil.

The principle of operation of the device, the possibility of its operation in certain conditions, the possible maximum errors of the device can be established according to symbols, printed on the dial of the device.

For example: (A) - ammeter; (~) - alternating current ranging from 0 to 50A; () - vertical position, accuracy class 1.0, etc.

Current and voltage measuring transformers have ferromagnetic magnetic cores on which the primary and secondary windings are located. The number of turns of the secondary winding is always greater than the primary.

The terminals of the primary winding of the current transformer are designated by the letters L1 and L2 (line), and the secondary windings by I1 and I2 (measurement). According to safety regulations, one of the terminals of the secondary winding of the current transformer, as well as the voltage transformer, is grounded, which is done in case of insulation damage. The primary winding of the current transformer is connected in series with the object being measured. The resistance of the primary winding of the current transformer is small compared to the consumer resistance. The secondary winding is connected to the ammeter and current circuits of devices (wattmeter, meter, etc.). The current windings of wattmeters, meters and relays are rated at 5A, voltmeters, voltage circuits of wattmeters, meters and relay windings are rated at 100 V.

The resistance of the ammeter and the current circuits of the wattmeter is small, so the current transformer actually operates in short circuit mode. The rated current of the secondary winding is 5A. The transformation ratio of a current transformer is equal to the ratio of the primary current to the rated current of the secondary winding, and for a voltage transformer - the ratio of the primary voltage to the secondary rated current.

The resistance of the voltmeter and voltage circuits of measuring instruments is always high and amounts to at least a thousand ohms. In this regard, the voltage transformer operates in idle mode.

The readings of devices connected through current and voltage transformers must be multiplied by the transformation ratio.

TTI current transformers

TTI current transformers are intended: for use in electricity metering schemes for settlements with consumers; for use in commercial electricity metering schemes; for transmitting a measurement information signal to measuring instruments or protection and control devices. The transformer housing is non-separable and sealed with a sticker, which makes access to the secondary winding impossible. The secondary winding terminals are covered with a transparent cover, which ensures safety during operation. In addition, the lid can be sealed. This is especially important in electricity metering circuits, as it helps prevent unauthorized access to the secondary winding terminals.

The built-in tinned copper busbar of the TTI-A modification makes it possible to connect both copper and aluminum conductors.

Rated voltage - 660 V; nominal network frequency - 50 Hz; transformer accuracy class 0.5 and 0.5S; rated secondary operating current - 5A.

Technical characteristics of TTI transformers

Transformer modifications	Rated primary current of the transformer, A
TTI-A	5; 10; 15; 20; 25; 30; 40; 50; 60; 75; 80; 100; 120; 125; 150; 200; 250; 300; 400; 500; 600; 800; 1000
TTI-30	150; 200; 250; 300
TTI-40	300; 400; 500; 600
TTI-60	600; 750; 800; 1000
TTI-85	750; 800; 1000; 1200; 1500
TTI-100	1500; 1600; 2000; 2500; 3000
TTI-125	1500; 2000; 2500; 3000; 4000; 5000

Electronic analog devices are a combination of various electronic converters and a magnetoelectric device and are used to measure electrical quantities. They have high input impedance (low energy consumption from the measurement object) and high sensitivity. Used for measurements in high and high frequency circuits.

The operating principle of digital measuring instruments is based on converting the measured continuous signal into an electrical code displayed in digital form. The advantages are small measurement errors (0.1-0.01%) in a wide range of measured signals and high performance from 2 to 500 measurements per second. To suppress industrial interference, they are equipped with special filters. Polarity is selected automatically and indicated on the reading device. Contains output to a digital printing device. They are used to measure voltage and current, as well as passive parameters - resistance, inductance, capacitance. Allows you to measure frequency and its deviation, time interval and number of pulses.

Plan

Introduction

Current meters

Voltage measurement

Combined devices of the magnetoelectric system

Universal electronic measuring instruments

Measuring shunts

Instruments for measuring resistance

Determination of ground resistance

Magnetic flux

Induction

Bibliography

Introduction

Measurement is the process of finding the value of a physical quantity experimentally, using special technical means - measuring instruments.

Thus, measurement is an informational process of obtaining experimentally a numerical relationship between a given physical quantity and some of its values, taken as a unit of comparison.

The main parameters of electrical circuits are: current, voltage, resistance, current power. Electrical measuring instruments are used to measure these parameters.

Measuring the parameters of electrical circuits is carried out in two ways: the first is a direct measurement method, the second is an indirect measurement method.

Electrical measuring instruments are classified as follows: according to the measured and reproducible physical quantity (ammeter, voltmeter, ohmmeter, frequency meter, etc.); by purpose (measuring instruments, measures, measuring transducers, measuring installations and systems, auxiliary devices); by the method of providing measurement results (displaying and recording); by measurement method (direct assessment devices and comparison devices); by method of application and design (panel, portable and stationary); according to the operating principle (electromechanical - magnetoelectric, electromagnetic, electrodynamic, electrostatic, ferrodynamic, induction, magnetodynamic; electronic; thermoelectric; electrochemical).

In this essay I will try to talk about the device, the operating principle, and give a description and brief description of electrical measuring instruments of the electromechanical class.

Current measurement

The most common ammeters are those in which the moving part of the device with the pointer rotates through an angle proportional to the magnitude of the current being measured.

Ammeters are magnetoelectric, electromagnetic, electrodynamic, thermal, induction, detector, thermoelectric and photoelectric.

Technical data of some types of domestic ammeters, milliammeters, microammeters, magnetoelectric, electromagnetic, electrodynamic, and thermal systems are given in Table 1.

Table 1. Ammeters, milliammeters, microammeters

Instrument system	Device type	Accuracy class	Measurement limits
Magnetoelectric	M109	0,5	1; 2; 5; 10 A
	M109/1	0,5	1.5-3 A
	М45М	1,0	75mV
	М45М	1,0	75-0-75mV
	M1-9	0,5	10-1000 µA
	M109	0,5	2; 10; 50 mA
	200 mA
	М45М	1,0	1.5-150 mA
Electromagnetic	E514/3	0,5	5-10 A
	E514/2	0,5	2.5-5 A
	E514/1	0,5	1-2 A
	E316	1,0	1-2 A
	3316	1,0	2.5-5 A
	E513/4	1,0	0.25-0.5-1 A
	E513/3	0,5	50-100-200 mA
	E513/2	0,5	25-50-100 mA
	E513/1	0,5	10-20-40 mA
	E316	1,0	10-20 mA
Electrodynamic	D510/1	0,5	0.1-0.2-0.5-1-2-5 A
Thermal	E15	1,0	30;50;100;300 mA

Voltage measurement

Voltmeter - direct reading measuring device for determining voltage or EMF in electrical circuits (Fig. 3). Connected in parallel to the load or source of electrical energy (Fig. 4).

Table 2. Voltmeters and millivoltmeters

Instrument system	Device type	Accuracy class	Measurement limits
Electrodynamic	D121	0,5	150-250 V
D567	0,5	15-600 V
Magnetoelectric	M109	0,5	3-600 V
M250	0,5	3; 50; 200; 400 V
М45М	1,0	75 mV;
75-0-75 mV
75-15-750-1500 mV
M109	0,5	10-3000 mV
Electrostatic	C50/1	1,0	30 V
C50/5	1,0	600 V
C50/8	1,0	3 kV
S96	1,5	7.5-15-30 kV
Electromagnetic	E515/3	0,5	75-600 V
E515/2	0,5	7.5-60 V
E512/1	0,5	1.5-15 V
With electronic converter	F534	0,5	0.3-300 V
Thermal	E16	1,5	0.75-50 V

For measurements in direct current circuits, combined instruments of the magnetoelectric system, ampere-voltmeters, are used. Technical data on some types of devices are given in Table 3.

Table 3. Combined devices of the magnetoelectric system.

Name	Type	Accuracy class	Measurement limits
Millivolt-milliammeter	M82	0,5	15-3000 mV; 0.15-60 mA
Voltammeter	M128	0,5	75mV-600V; 5; 10; 20 A
Ampere-voltmeter	M231	1,5	75-0-75 mV; 100-0-100 V;0.005-0-0.005 A; 10-0-10 A
Voltammeter	M253	0,5	15mV-600V; 0.75 mA-3 A
Millivolt-milliammeter	M254	0,5	0.15-60 mA; 15-3000 mV
Microamperevoltmeter	M1201	0,5	3-750 V; 0.3-750 µA
Voltammeter	M1107	0,2	45mV-600V; 0.075 mA-30 A
Milliamp-voltmeter	М45М	1	7.5-150 V; 1.5 mA
Volt-ohmmeter	M491	2,5	3-30-300-600 V; 30-300-3000 kOhm
Ampere-voltmeter	M493	2,5	3-300 mA; 3-600 V; 3-300 kOhm
Ampere-voltmeter	M351	1	75mV-1500V;15uA-3000mA;200Ohm-200Mohm

Technical data on combined instruments - ampere-voltmeters and ampere-voltmeters for measuring voltage and current, as well as power in alternating current circuits.

Universal electronic measuring instruments