RU2079102C1 - Method for tuning of integral strain-measuring bridge using power supply - Google Patents

Abstract

FIELD: instruments. SUBSTANCE: method involves measuring of resistance of power supply diagonal of strain-measuring bridge for different temperature values, measuring of variation range of output signal of strain-measuring bridge for same temperature values when strain-measuring bridge is fed by power supply, connection of temperature-stable resistor in parallel to power supply diagonal of strain-measuring bridge, measuring initial output signal from strain-measuring bridge and additional of compensating resistor in one are of bridge. Resistance of power supply diagonal of strain-measuring bridge is measured for three different temperature values which correspond to lower, middle and upper points of temperature variation range. Before connection of temperature-stable resistor, additional resistor which resistance depends on temperature in same way as that of power supply diagonal is connected in series to power supply diagonal of strain-measuring bridge. Said temperature-stable resistor is being connected in parallel to power supply diagonal and temperature-sensitive resistor. Then initial output signal from strain-measuring bridge is measured when bridge is fed by power supply for two temperature values which correspond to lower and upper limits of temperature variation range. Then variation range of output signal for temperature which corresponds to middle points of temperature variation range is measured. Value of resistance of compensating resistor is calculated. Said compensating resistor is made from material which temperature sensitivity coefficient is by two orders of magnitude greater than temperature sensitivity coefficient of strain-measuring resistors. EFFECT: increased precision. 2 dwg

Description

 The invention relates to measuring equipment, and in particular to methods of tuning integrated strain gauge bridges designed to operate in variable temperatures.

 There is a method of tuning an integrated strain gage powered by a current source, which consists in measuring the resistance of the power supply diagonal of the strain gage at two different temperatures, measuring the initial output signal of the strain gage when it is powered from a constant voltage source for the same two temperatures, using the data obtained, determine the required the voltage value at the output of the strain bridge, then this voltage is established by introducing a place in one of the arms depending on the sign of the additive temperature sensitivity elnosti, compensation resistor made of the same material as the other resistors tenzomosta / 1 /.

 The disadvantage of this tuning method is that it allows you to stabilize only the initial output signal of the strain gage.

 The closest technical solution is the method of setting up an integrated strain gage powered by a current source, which means that to stabilize the sensitivity of the strain gage, a thermostable resistor is connected in parallel to the strain gage power diagonals, the resistances of which are determined from the measurement results of the resistance of the power diagonal at two different temperatures and according to the measurement results of the range changes in the output signal for the same temperatures when feeding the strain gage from the current source, and th correction of the initial output signal is carried out by introducing the post into the shoulders of compensation resistors, the resistances of which are selected by setting output tenzomosta desired voltage value based on the results of measuring the initial output signal for the same two values of the temperature when supplied from a voltage source axle / 2 /.

However, this method has the following disadvantage. The temperature correction of sensitivity in the described way depends on the temperature coefficient of resistance (TCS) of the diagonal of the strain gage power supply and is not effective enough when this coefficient is small (1 • 10 ^-5 5 • 10 ^-5 1 / ^o C), and when the temperature coefficient of elastic modulus is subject to , on which the strain gage is formed, is opposite in sign to the temperature coefficients of the strain gages, the described method is even more ineffective.

где R_т1(T₂) значение сопротивления термозависимого резистора при температуре Т₂, Ом
R(Т₁), R(Т₂), R(Т₃) сопротивление диагонали питания тензомоста при температурах Т₁, Т₂, Т₃ соответственно, Ом,
α_RC ТКС термостабильного резистора, 1/^oC,
V_тр<V_д(Т₁) нормативная величина диапазона изменения выходного сигнала тензомоста от воздействия номинального значения измеряемой величины, мВ,
V_д(Т₁), V_д(Т₂), V_д(Т₃) - диапазоны изменения выходного сигнала тензомоста от воздействия измененного значения измеряемой величины при температурах Т₁, Т₂, Т₃ соответственно, мВ,
α $\genfrac{}{}{0ex}{}{\text{+}}{\text{Rти}}$ ,α $\genfrac{}{}{0ex}{}{\text{-}}{\text{Rти}}$ ТКС термозависимого резистора в интервале температур от Т₂ до Т₃ и от Т₂ до Т₁ соответственно, 1/^oC,
Т₁, Т₂, Т₃ значения температуры, соответствующие нижней, средней и верхней точкам рабочего диапазона температур тензомоста, С.The technical task of the method is to increase accuracy by stabilizing the sensitivity
The technical result is achieved by the fact that in the tuning method, which includes measuring the resistance of the strain gage power diagonal at different temperatures, measuring the range and changing the output signal of the strain gage for the same temperatures when supplying the strain gage from a current source, connecting a thermostable resistor to the strain gage power diagonal, measuring the initial output signal strain bridge and the introduction into one of the shoulders of the bridge thermal compensation resistor, measuring the resistance of the power diagonal of the strain bridge and d The output signal changes range is carried out at three different temperatures, corresponding to the lower, middle and upper points of the operating temperature range. Before connecting the thermostable resistor, a thermo-dependent resistor with a TCS of the same sign as that of the bridge diagonal is connected in series with the power diagonal, and the thermostable resistor is connected in parallel inclusions in series of the power diagonal and the temperature-dependent resistor, and to determine the values of the resistance of the temperature-dependent and thermostable resistors use the expressions:

where R _t1 (T ₂ ) is the resistance value of a temperature-dependent resistor at a temperature of T ₂ , Ohm
R (T ₁ ), R (T ₂ ), R (T ₃ ) the resistance of the diagonal of the strain bridge power supply at temperatures T ₁ , T ₂ , T _3, respectively, Ohm,
α _RC TCS thermostable resistor, 1 / ^o C,
V _Tr <V _d (T ₁ ) the standard value of the range of the output signal of the strain bridge from the influence of the nominal value of the measured value, mV,
V _d (T ₁ ), V _d (T ₂ ), V _d (T ₃ ) - ranges of changes in the output signal of the tensor bridge from the influence of the changed value of the measured value at temperatures T ₁ , T ₂ , T _3, respectively, mV,
α $\genfrac{}{}{0ex}{}{\text{+}}{\text{Rti}}$ , α $\genfrac{}{}{0ex}{}{\text{-}}{\text{Rti}}$ TCS of a temperature-dependent resistor in the temperature range from T ₂ to T ₃ and from T ₂ to T _1, respectively, 1 / ^o C,
T ₁ , T ₂ , T ₃ temperature values corresponding to the lower, middle and upper points of the operating temperature range of the tensor bridge, C.

где: R_T0(Т₂) значение сопротивления компенсационного резистора при температуре Т₂, Ом,
V_д(Т₂) диапазон изменения выходного сигнала тензомоста от воздействия номинального значения измеряемой величины при температуре Т₂, измеряемый до подключения резисторов R_Ти, R_с, мВ,

диапазон изменения выходного сигнала тензомоста от воздействия измененного значения измеряемой величины при температуре T₂, измерений после подключения резисторов R_Ти, R_с мВ,
α_RTo ТКС компенсационного резистора, 1/^oС,
V_н(Т₁), V_н(Т₃) значения начального выходного сигнала тензометра при температурах Т₁, Т₃ соответственно, мВ,
I_пит(Т₁), I_пит(Т₃) значения тока питания тензомоста при температурах Т₁, Т₃ соответственно, МА.Then, the initial output signal of the strain gage is measured when it is powered from the current source for two temperature values corresponding to the lower and upper points of the working temperature range, the range of the output signal is measured at a temperature corresponding to the midpoint of the working temperature range, and the value of the compensation resistance is determined from the obtained data a resistor designed for the temperature correction of the initial output signal and made of material with TCS two orders of magnitude you TKS strain gages, according to the formula:

where: R _T0 (T ₂ ) is the resistance value of the compensation resistor at a temperature of T ₂ , Ohm,
V _d (T ₂ ) the range of the output signal of the strain gage from the influence of the nominal value of the measured value at temperature T ₂ , measured before connecting the resistors R _Ti , R _s , mV,

the range of the output signal of the strain gauge from the impact of the changed value of the measured value at temperature T ₂ , measurements after connecting the resistors R _Ti , R _with mV,
α _RTo TCS compensation resistor, 1 / ^o С,
V _n (T ₁ ), V _n (T ₃ ) the values of the initial output signal of the strain gauge at temperatures T ₁ , T _3, respectively, mV,
I _pit (T ₁ ), I _pit (T ₃ ) the current values of the tensor bridge power supply at temperatures T ₁ , T _3, respectively, MA.

 A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known one in that, to stabilize the sensitivity, the strain gage power supply circuit additionally includes a temperature-dependent resistor having the same sign TCS with the strain gage power supply diagonal, and the thermally dependent resonator is connected in series with the motor supply of the strain gage, and thermostable parallel to the diagonal of the strain gage power supply and the temperature-dependent resistor.

 The resistance of the thermally dependent and thermostable resistors is determined by measuring the resistance of the load bridge diagonal at three different temperatures and by measuring the range of the output signal for the same temperatures when the bridge is powered by a current source.

 The temperature correction of the initial output signal is carried out by including in one of the arms of the compensation cavity with the TCS two orders of magnitude more TCS strain gages, the resistance of which is determined by the measurement results and the initial output signal for two temperatures corresponding to the lower and upper temperatures of the operating temperature range and the measurement result the range of the output signal at a temperature corresponding to the midpoint of the operating temperature range.

 In FIG. 1 presents an example of a topology and in FIG. 2 an electrical diagram of an integrated tensor bridge for adjustment by the proposed method.

The integrated strain gage contains working strain gages R ₁ - R ₄ , a compensation resistor R _that is made of a material with a TCS two orders of magnitude larger than a TCS strain gages and shorted in the initial state by a jumper P1, contact pads K1-K7, as well as an additional thermally dependent resistor R _ty with jumpers P ₂ -P ₇ having a TKS of the same sign with the TKS of the diagonal of the tensonast nutrition.

The values of the resistances R _then , R _ty during designing are chosen such that they exceed the longitudinally necessary temperature compensation.

The additional resistor R _c is located outside the substrate on which the tensor bridge is formed, and is a constant thermostable resistor, for example, type C2-36.

 Adjustment of the integrated tensor bridge is as follows.

At three different temperatures T ₁ , T ₂ , T ₃ corresponding to the lower, middle, and upper points of the operating temperature range of the strain gage, measure the resistance of the power supply diagonal of the strain gage R (T ₁ ), R (T ₂ ), R (T ₃ ) between the pads K ₂ and K ₇ .

The temperature T _{2 is} chosen, as a rule, equal to the temperature of normal climatic conditions (25 + 10) ^o C. Connect the diagonal of the power supply to the current source and measure the range of the output signal of the tensor bridge from the influence of the nominal value of the measured value for the same temperature values V _d (T ₁ ), V _d (T ₂ ) and V _d (T ₃ ) at a fixed value of the supply current I _pit . The resistance values of the additional thermally dependent resistor R _{ty are} calculated by the formula (I). By breaking the jumpers P ₁ -P ₆ , the calculated values of R. are determined. Calculate the resistance value of the thermostable resistor P _c according to formula (2) and choose from a number of constant resistors, for example, type C2-36 ОЖО, 467, 089 TU with TKS no more than + 75 ^-6 1 / ^o C in the temperature range from minus 60 to +155 ^o C, the closest (within + 0.5%) at face value to the calculated value.

They include the resistors R _ty and R _c in the measuring circuit and connect the diagonal of the circuit power to the current source. At temperatures T ₁ and T ₃ measure the value of the initial output and the signal of the strain gage and at temperature T _{2 the} range of changes in the output power from the change in the nominal value of the measured value. Calculate the resistance values of the compensation resistor according to formula (3) and include it in one of the shoulders of the place, depending on the sign of the temperature change in the initial output signal, having previously removed the jumper P ₁ . The required value of the resistance of the compensation resistor is selected by short-circuiting individual sections of the compensation resistor with jumpers made of gold microwire.

 Setting the tensor bridge in the described way allows you to stabilize its sensitivity and the initial level of the output signal when working in a wide range of variable temperatures.

 The physical meaning of the process of compensating for temperature changes in sensitivity and the initial output signal is as follows.

 When working in conditions of variable temperatures, the sensitivity of the strain gage changes. The magnitude of the sensitivity change depends on the TCS of the strain gages, on the temperature coefficient of the strain sensitivity of the material of the strain gages, on the temperature coefficient of the elastic modulus of the substrate on which the strain gage is formed.

 Bypassing the diagonal of the strain gage power supply with a thermostable resistor causes a distribution of the supply current between the diagonal of the strain gage and the shunt resistor. When the temperature changes, the resistance of the power diagonal changes due to its TCS, which leads to the redistribution of current between the thermostable resistor and the power diagonal of the strain gage.

 By appropriately calculating the resistance of the thermostable resistor, it is possible to compensate for the temperature change in sensitivity and strain gage by an inversely proportional change in the current flowing through the power diagonal.

However, this compensation method is effective only with a sufficiently large TCS value of the power diagonal. If the TCS of the supply diagonal is ≈5 • 10 ^-5 1 / ^o C, and the magnitude of the sensitivity change is usually greater than the value by which it can be compensated by the change in the bridge supply current.

 This drawback is eliminated in the method of adjusting the power supply diagonal by increasing the TCS by the required value by turning on a thermally dependent resistor in series with the power supply diagonal with the TCS of the same sign as the supply diagonal TCS. In this case, the thermostable resistor is connected in parallel with the thermally dependent resistor and the power diagonal. The resistance of the thermally dependent and thermostable resistors is calculated so that any temperature change in sensitivity is compensated by an inversely proportional change in the supply current of the bridge.

The effectiveness of the proposed tuning method is confirmed experimentally. The results of experimental studies are shown in table 1. The determination of temperature errors was carried out in the temperature range from minus 60 to +165 ^o C.

For existing strain gauge pressure sensors, for example, W206, W212, the temperature errors of zero and sensitivity are respectively + 0.02% ^o C and + 0.05% ^o C. Thus, the experimental results show that the adjustment of the proposed method allows to increase by an order of magnitude the stability of the initial output signal and the sensitivity of the strain gauges in the temperature range from minus 60 to +165 ^o C.

 The derivation of formulas (1), (2) is carried out as follows.

When powered by direct current tenzomosta tenzomosta output signal (and the range of variation of the output signal V _d (T) associated with a current power ratio I _pit tenzomosta
u _d (T) = ΔR (T) • I _pit (4)
where ΔR (T) is the change in the resistance of the shoulders of the strain gage from the input quantity (for example, pressure).

R_ти(T₂) = R_ти(T_i)•[1+α_Rти•(T₂-T_i)], (7)
I_c+I_д=I_пит (8)

где R_с(Т₂), R_с(Т_i) значение сопротивления термостабильного резистора при значениях температуры Т₂ или Т_i, принимающей значение Т₁ при i=1 или Т₃ при i=3 соответственно,
α_RC температурный коэффициент сопротивления (ТКС) термостабильного резистора в интервале температур от Т₂ до Т_i,
R(Т₂), R(Т_i) значения сопротивления диагонали питания тензомоста при значениях температуры Т2 и Т_i соответственно,
R_ти(T₂), R_ти(Т_i) -значения сопротивления термозависимого резистора при значениях температуры Т₂ и Т_i,
α_RTи ТКС термозависимого резистора и интервала температур от Т₂ до Т_i,
I_c, I_д значения тока, протекающего через резисторы R_c и R_ти соответственно,
I_пит значение тока питания схемы.When you turn on the DC source according to the proposed scheme, the following relationships are true:
R _c (T ₂ ) = R _c (T _i ) • [1 + α _RC • (T ₂ -T _i )], (5)

R _ty (T ₂ ) = R _ty (T _i ) • [1 + α _Rti • (T ₂ -T _i )], (7)
I _c + I _d = I _pit (8)

where R _c (T ₂ ), R _c (T _i ) is the resistance value of the thermostable resistor at temperatures T ₂ or T _i taking the value T ₁ at i = 1 or T ₃ at i = 3, respectively
α _RC temperature coefficient of resistance (TCS) of thermostable resistor in the temperature range from T ₂ to T _i ,
R (T ₂ ), R (T _i ) are the resistance values of the diagonal of the strain gage power supply at temperatures T2 and T _i, respectively,
R _ty (T ₂ ), R _ty (T _i ) are the values of the resistance of the thermally dependent resistor at temperatures T ₂ and T _i ,
α _{RT and} TCS of a temperature-dependent resistor and a temperature range from T ₂ to T _i ,
I _c , I _{d the} value of the current flowing through the resistors R _c and R _ty, respectively,
I _pit value of the current supply circuit.

С учетом формулы (10)

Или

Обознач.I _pit = const
u _Tr = ΔR (T) • I _d = const
where V _{Tr the} desired value of the output signal, V _Tr <V (T _i , V _Tr <V (T ₂ )
At

Given the formula (10)

Or

Designated by

Получаем

С другой стороны

Сделав необходимые преобразования после раскрытия скобок, получаем:

Обозначив:

Получаем

Или
R $\genfrac{}{}{0ex}{}{\text{i}}{\text{ти}}$ (T₂)•(C_i-B_i) = R(T₂)•(A_i-C_i) (25)
Или

В общем случае
R $\genfrac{}{}{0ex}{}{\text{1}}{\text{ти}}$ (T₂) ≠ R $\genfrac{}{}{0ex}{}{\text{3}}{\text{ти}}$ (T₂) (27)
Поэтому расчет значения термозависимости резистора для интервала температур проведены по формуле:

Переобозначив

производя необходимые подстановки, получаем выражение для R_Ти(Т₂) в общем виде

Формулу для расчета R_то(Т₂) получаем, исходя из известного выражения для расчета термокомпенсационного сопротивления нуля (Проектирование датчиков для измерения механических величин под ред. Е.П.Осадчего, М, Машиностроение, 1979г.)

где r_β значение термокомпенсационного сопротивления нуля,
a_r ТКС поста,
α_β ТКС компенсационного сопротивления,
r сопротивление одного плеча моста.

We get

On the other hand

Having made the necessary transformations after expanding the brackets, we get:

By marking:

We get

Or
R $\genfrac{}{}{0ex}{}{\text{i}}{\text{tee}}$ (T ₂ ) • (C _i -B _i ) = R (T ₂ ) • (A _i -C _i ) (25)
Or

In general
R $\genfrac{}{}{0ex}{}{\text{one}}{\text{tee}}$ (T ₂ ) ≠ R $\genfrac{}{}{0ex}{}{\text{3}}{\text{tee}}$ (T ₂ ) (27)
Therefore, the calculation of the temperature dependence of the resistor for the temperature range is carried out according to the formula:

Redesignating

making the necessary substitutions, we obtain the expression for R _Ti (T ₂ ) in the general form

The formula for calculating R _then (T ₂ ) is obtained on the basis of the well-known expression for calculating thermal compensation zero resistance (Design of sensors for measuring mechanical quantities under the editorship of E.P. Osadchy, M, Mechanical Engineering, 1979)

where r _{β is the} value of the temperature compensation resistance of zero,
a _r TKS post,
α _β TCS compensation resistance,
r resistance of one shoulder of the bridge.

To determine the TCS of the bridge, it is necessary to know the magnitude of the output signal from the strain bridge at two temperatures: T ₁ and T ₃ .

где V_н(Т₃), V_н(T₁) величины выходного сигнала тензомоста при температурах Т₃ и Т₁ соответственно.The calculation is carried out according to the formula:

where V _n (T ₃ ), V _n (T ₁ ) the output signal of the tensor bridge at temperatures T ₃ and T ₁ respectively.

K = r1 / r2 = r3 / r4 is the symmetry coefficient of the bridge (usually K = 1),
V _pit supply voltage of the bridge.

После подставки выражения для α_r, формулы для r_β получим

Поскольку V_пит(Т) R(Т)•I_пит(Т),
где R(Т) сопротивление диагонали питания при питании тензомоста от источника постоянного тока,
I_пит(Т) ток питания тензомоста.Since the output signal of the strain gage is directly proportional to the supply voltage and the measurements of the output signal at different temperatures are spaced in time to eliminate the effect of instability, the calculation of the bridge TCS should be carried out according to the formula:

After substituting the expression for α _r , the formula for r _β we get

Since V _pit (T) R (T) • I _pit (T),
where R (T) is the resistance of the power diagonal when feeding the strain bridge from a DC source,
I _pit (T) current supply of the strain gage.

Вследствие малости ΔR (Т) (доли Ом) зависимостью ΔR от температуры можно пренебречь

или

С учетом этого в формулу для r_β введен коэффициент, равный отношению диапазонов изменения выходного сигнала до и после введения термокомпенсации чувствительности:

Преобразовав термокомпенсационное сопротивление нуля и его ТКС
r_β= β_то(T₂) α_β= α_Рто
и введя новые обозначения в выражение (41), получаем выражение (3) для значения сопротивления компенсационного резистора при температуре Т₂.Given that
u _d (T) = ΔR (T) • I _pit (T) (36)
and the actual supply current of the strain gage depends on the degree of damping of the sensitivity due to additional resistances R _Ti and R _s , and

Due to the smallness of ΔR (T) (fraction of Ohm), the temperature dependence of ΔR can be neglected

or

With this in mind, a coefficient equal to the ratio of the ranges of the output signal before and after the introduction of thermal compensation of sensitivity was introduced into the formula for r _β :

By transforming the thermal compensation resistance of zero and its TCS
r _β = β _then (T ₂ ) α _β = α _Рто
and introducing new notation in expression (41), we obtain expression (3) for the resistance value of the compensation resistor at temperature T ₂ .

The effectiveness of the proposed tuning method is confirmed experimentally. The results of experimental studies are shown in table 2. The determination of temperature errors was carried out in the temperature range from minus 60 to +165 ^o C.

For existing strain gauge pressure sensors, for example W206, W212, the temperature errors of zero and sensitivity are respectively + 0.02% / ^o C and + 0.05% / ^o C. Thus, the experimental results show that the adjustment by the proposed method allows order to increase the stability of the initial output signal and the sensitivity of the strain gauges in the temperature range from minus 60 to +165 ^o C.

Claims (1)

A method for setting up an integrated strain gauge bridge powered by a current source, which consists in measuring the resistance of the strain gauge power diagonal at different temperatures, measuring the range of the output signal of the strain gauge for the same temperature values when feeding the strain gauge from the current source, then connect the thermostable resistor parallel to the strain gauge power diagonal , measure the initial output signal of the strain gage and introduce into one of the shoulders a compensating resistor, characterized in that the resistance of the diagonal of the feed the tensor bridge and the range of the output signal are measured at three different temperatures, corresponding to the lower, middle and upper points of the operating temperature range; before connecting the thermostable resistor, a thermally dependent resistor with a temperature coefficient of resistance of the same sign as the diagonal of the bridge power supply is connected in series with the power diagonal, moreover, the thermostable resistor is connected in parallel with the power diagonal and the thermally dependent resistor connected in series with it, and for The values of the resistance values of the thermally dependent and thermostable resistors use the expressions

wherein _{T and} R are temperature dependent resistance value of the resistor at the temperature T _2, in ohms;
R (T ₁ ), R (T ₂ ), R (T ₃ ) the resistance of the diagonal of the strain bridge power supply at temperatures T ₁ , T ₂ , T _3, respectively, Ohm;
α _RC TCS thermostable resistor, ^o C ^-1 ;
U _tp <U _d (T ₁ ) the standard value of the range of the output signal of the strain gage from the influence of the nominal value of the measured value, mV;
U _d (T ₁ ), U _d (T ₂ ), U _d (T ₃ ) are the ranges of the output signal of the tensor bridge from the influence of the nominal value of the measured value at temperatures T ₁ , T ₂ , T _3, respectively, mV;
α $\genfrac{}{}{0ex}{}{\text{+}}{\text{Rti}}$ , α $\genfrac{}{}{0ex}{}{\text{-}}{\text{Rti}}$ TCS of a temperature-dependent resistor in the temperature range from T ₂ to T ₃ and from T ₂ to T _1, respectively, ^o C ^-1 ;
T ₁ , T ₂ , T ₃ the temperature value corresponding to the lower, middle and upper points of the operating temperature range of the tensor bridge, ^o C,
then measure the initial output signal of the strain gage when it is supplied from the current source for two temperature values corresponding to the lower and upper points of the operating temperature range, measure the range of the output signal at a temperature corresponding to the midpoint of the operating temperature range, and to determine the resistance value of the compensation resistor made from a material with a temperature coefficient of resistance two orders of magnitude higher than the temperature coefficient of resistance of strain gauges, using zuyut expression

where R _o (T ₂ ) is the resistance value of the compensation resistor at a temperature of T ₂ , Ohm;
U _d (T ₂ ) the range of the output signal of the strain gage from the influence of the nominal value of the measured value at a temperature T ₂ measured before connecting the resistors R _ty , R _c , mV;

the range of the output signal of the strain gage from the influence of the nominal value of the measured value at a temperature T ₂ measured after connecting the resistors R _ty , R _c , mV;

TCS compensation resistor, ^o C ^-1 ;
U _n (T ₁ ), U _n (T ₂ ) the values of the initial output signal of the tensor bridge at temperatures T ₁ and T _3, respectively, mV;
I _pit (T ₁ ), I _pit (T ₃ ) values of the current supply of the strain bridge at temperatures T ₁ and T _3, respectively, mA.

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