SU1610328A1 - Strain-measuring device - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure pressure. The purpose of the invention is to improve the measurement accuracy. The device contains a power source 1, the first voltage divider, consisting of resistors 2 and 3, the midpoint of which is connected to the inverting input of the operational amplifier 4, the second voltage divider containing the strain gages 5 and 6, the middle point of which is connected to the non-inverting input of the amplifier 4 the third voltage divider, the midpoint of which is connected to the inverting input of the second operational amplifier 7. In turn, the resistor 10 is connected between the resistor 11 and the second resistor 5, and the resistor 2 between the inverting the input of the amplifier 4 and the non-inverting input of the amplifier 7. The device is additionally equipped with a second adder 13, a buffer amplifier 14 and a second large-scale amplifier 15. 1 Il.

Description

one

(21) 4628439 / 2A-10

(22) 12/29/88

(46) 11/30/90. BULL. No. 44

(71) State Research Institute of Heat and Power Instrumentation

(72) A.U.Yalshev

(53) 531.787 (088.8)

(56) USSR Copyright Certificate №932212, кп. G 01 B 7/18, 1982.

(54) TENSOMETRY DEVICE

(57) The invention relates to a measurement technique and can be used to measure pressure. The purpose of the invention is to increase the measurement accuracy. The device contains a power source 1, the first voltage divider, consisting of resistors

2 and 3, the middle point of which is connected to the inverting input of the operational amplifier 4, the second voltage divider containing the strain resistors 5 and 6, the middle point of which is connected to the non-inverting input of the amplifier 4, the third voltage divider, the middle point of which is connected to the inverter input . the second operational amplifier 7. In turn, the resistor 10 is connected between the resistor 11 and the second resistor, and the resistor 2 between the inverting input of the amplifier 4 and the non-inverting input of the amplifier 7. The device is additionally equipped with a second adder 13, a buffer amplifier 14 and the second large-scale amplifier 15. 1 il.

i (L

316

The invention relates to a measurement technique, namely, strain gauge devices with a strain-resistive measuring circuit, and can be used to measure mechanical loads, e.g. pressure, under conditions of significant influence of fast temperatures.

The purpose of the invention is to improve the measurement accuracy by reducing the non-linearity of the transformation and the multiplicative component of the temperature error.

The drawing shows a block diagram of the proposed device.

The device contains a grounded power source 1, which for the strain circuit as a reference voltage signal, the first 2 and second 3 resistors, which form a voltage divider, operational amplifier 4 with differential inverting and non-inverting inputs, to the inverting input of which is connected the middle point of this divider, two series-connected strain gauges 5 and 6, one of which (the strain gauge 6) is grounded, forming the other (second) voltage divider, the middle point of which is connected to the second (non-inverting) input of the operational amplifier 4, in the negative feedback circuit of which resistor 3 is connected, serially connected to the second operational amplifier 7, also with differential inputs, scale amplifier 8 and adder 9, the second input of which is connected to the output of the first operational amplifier 4 and the third 10, fourth 11 and fifth 12 resistors connected in series with each other. The fourth and fifth resistors form the third voltage divider, the midpoint of which is connected to the inverting input of the operational amplifier 7 ,. resistor 12 is connected to the negative feedback circuit. In turn, resistor 10 is connected between resistor 11 and strain gauge 5, and resistor 2 is connected between the inverting input of opamp 4 and the non-inverting input of opamp 7.

In addition, the device is additionally equipped with a second adder 13 with three inputs, a buffer amplifier 14. with a single gain and

284

the second large-scale amplifier 15, the power source 1 being connected to one of the inputs of the adder 13, to the other two inputs of which the output of the buffer amplifier and the output of the scale amplifier 15 are connected, the input of which is connected to the output of the operational amplifier 7, and the input b5 of the power amplifier is connected to the common connection point of the tensorizer 5 with the resistor 10, the common connection point of which with the resistor 11 is directly connected to the output of the adder 13, while the non-inverting input of the operational amplifier 7 is connected to the output have a buffer amplifier.

Strain gauge device contains internal and external PS Evdomosty, interconnected according to the so-called scheme of the bridge in the bridge.

The internal pseudo-bridge is made up of an operational amplifier 4, strain gauges 5 and 6, resistors 2 and 3, and

also a unity gain buffer amplifier 14.

An external pseudo-bridge is formed by an operational amplifier.7, a buffer amplifier 14, resistors 11 and 12, as well as a resistor 10 and strain gauges 5 and 6. At the same time, the buffer amplifier potentially isolates the internal pseudo-bridge from the external one, at the output of which voltage U (and Uj respectively.

The device works as follows.

When exposed to pressure P, the strain resistors 5 and 6, respectively, perceive compression and tension deformation in such a way that the resistance Kg of the tension sensor 5 decreases, and the resistance R of the strain gauge 6 increases. Since the strain gauges are in the same temperature conditions, the change in their resistances is almost the same value as the linear deformation 6.

I.

From the output of the operational amplifier 4, which is included in the above internal internal host, the main informative signal U, which is modified by the algorithm

„- t, RzRe -. КзК, - R2 (R5 + Кб)

(one)

516

where is the voltage taken

from the output of the buffer amplifier}

R- and RJ - resistance of resistors 2 and 3, respectively.

In turn, the additional signal Ugi used in the device for temperature correction is removed from the output of amplifier 7 entering the above external pseudo-bridge:

()

where and is the voltage taken from the output of the adder 13; R. and R, ji are the resistances of resistors 11 and 12, respectively.

In this case, the output voltage of the adder 13 is formed according to

and, Un + and

4 - K, 5U2,

(3)

where and is the output voltage of the power source 1, K,. is the scaling factor

scale amplifier 15. At the output of the buffer amplifier 14, a signal U is formed, equal to

Rg + Re

and.

and

 Ry + KB + RIO

(four)

where R, 0 is the resistance of the resistor 10. Taking into account the expressions (1) - (4), we obtain the following main dependencies for the bridge bridge circuit:

and. and,

RtRs - RiRio

1 +

..RS + R6 EIZ

 5 R, (, R ,, /

-1 - K, g (

RS + Rg Rtt-v V

40

.

R5 (P, UT) Rs (e, UT) + o.UT) 1 - Ke (1 + lfuT) J;

R, - (P, UT) R6 (e, UT)

"RO (I) l + K6 (1 -" - yT

where K is the coefficient of strain sensitivity (KTP) of the strain gauge /

оС - temperature coefficient of resistance (ТКС) of the strain gauge,

LP is the temperature coefficient of the stress sensitivity (DC) of the strain gauge,

RJJ is the nominal value of the resistance of the strain gauge at the calibration tee-Rati Go. Taking into account the statements (7) we get:

R5 (e, & T) + RfiCe.uDs i 2Rg (1 + YYT).

(eight)

Thus, one of the arms of the external pseudo-bridge with strain gauges 5 and 6 is thermo-dependent, and the change in its resistance is determined mainly by the TCR of these strain gauges.

Having fulfilled at the calibration temperature Tj the condition under which the ratio of the resistances of the resistors 11 and 12 of the external pseudo-bridge corresponds to Rt2 RS- + R6 corresponds to the equality -.- -

those. - effusion (5) and

RM fo (6) we get:

40

)(five)

(9)

. (6)

IT - n (5 + R6 RC), and o - and p (, -g-; "

f ioKII

 l - К „(V) l

| RIO R "J

With the simultaneous effect of pressure P and temperature DT for a differential pair consisting of strain gauges 5 and 6, the following relations can be presented as a first approximation, characterizing the change in resistance of these strain gauges:

45

 (ten)

1 - K.,

50 GD (R) - resistance change

the strain gauge under the influence of the fast-changing temperature T, with the DT DT T - Td Since there really is a ir 2uR (M)

the property of C.s-fT 1. then for OC | o

55

45

New and additional U signals we write:

and

 - g

 RzRi; L

1 +

to 2UR (UT) 1. 5 R, o J

(eleven)

U,

2AR (iT)

R

(12)

40

From expression (11) it follows that the main signal U, is sensitive to both pressure P and temperature, at the same time an additional signal and is sensitive mainly to the effect of temperature at the location of resistance strain gages 5 and 6.

Consequently, according to the expression (12), the external pseudo-bridge works practically as a temperature sensor, which generates the output signal Uj, in which (unlike the prototype) there is no parametric term depending on the measured pressure. In other words, the introduction into the circuit of the device of the adder 13 and the buffer amplifier 1A made it possible to substantially weaken the effect of the measured pressure on the temperature dependence of the signal Uj.

 Therefore, to extend the temperature range of operation of the strain gauge device, the signal U can be effectively used as a corrective signal.

The additional signal Ug thus generated is fed to large-scale amplifiers 8 and 15. With which help, respectively, correction signals KgU and K, 5Uj, are formed. The magnitude of the scaling factor Kg determines the depth of compensation of the additive component of the temperature error, and the magnitude of the coefficient K, the scaling determines the amplitude of the correction signal providing compensation for the multiplicative component of the temperature error.

When compensation additive composition. We establish the following condition: K, O and KD e O, as a result of which from the expressions. (5) and (6) we obtain, respectively, the following dependences;

, - ". .

The signal from the output of the operational amplifier 4 is fed to one of the inputs of the adder 9, to the second input of which from the output of the scale amplifier 8 is fed to the correction signal KgUn to compensate for the additive component of the temperature error.

In this case, the output of the adder 9 will generate a signal equal to

TI - n RzRe - R3Rs-,

EXIT -

+ If IT fRg-- R6) -H KgU (- R;)

0

five

0

five

0

five

0

five

or taking into account the expression (12) we obtain:

tm tt R2R6 (TsAT) - R, RS (XRT) 6b1) With nR2.Rfa

 Key (15)

  R When the condition R Rg const is fulfilled, the last expression is simplified and leads to

I

IIII GK (E.LT) -. (& T).

and, „and„ R, o

(16) Analysis of expression (16) shows

that in the proposed device the compensation of the additive component of the temperature error is more efficient than in the prototype, while the conversion functions for the signals and and and are more linear than the similar functions of the prototype conversion.

In order to compensate for the multiplicative component, a large-scale amplifier 15 is used, the output signal from which (at 0) is applied to one of the inputs of the adder 13. At the same time, the voltage of the tangency circuit is changed compared with the reference voltage U, generated by the source 1, which connected to the second input of the adder 13. To the third input of the adder 13 a signal U is fed from the output of the buffer amplifier, the value of which is almost equal to the supply voltage of the strain gages 5 and 6 of the measuring circuit. This connection of the buffer amplifier 14 with the adder 13 eliminates the influence of the measuring diagonal of the internal pseudo-bridge on the measuring diagonal of the external pseudo-bridge intended to generate an additional signal Ug about the effect of temperature. This is one of the main functional differences between the circuit of the proposed device and the prototype circuit.

Thus, when K 5 O and K, O, taking into account the impulses (11) and (12), the output signal of adder 9 generates an informative signal Ugjj, containing the components for compensating for temperature drifts zero and the measuring range:

and

 out

 KgKb - RiRg

R, R

 +

(17)

+ to - ALJAT). . to IT 2AR (UT) .5 R ,, J aUnR;

From the analysis of permutation (17), it follows that in the proposed device it is possible, at a rapidly changing temperature over a wide range, to separately perform autocompensation of both additive and multiplicative components of the temperature error.

Claims (1)

Invention Formula A strain gauge device containing two strain gauges, a power source, two operational amplifiers, a scale divider, an adder and five resistors, the inverting input of the first operational amplifier through the first connecting resistor five 0 five 0 five with the non-inverting input of the second operational amplifier and through the second resistor with its own output and one input of the adder, and the non-inverted 1st input of the first operational amplifier through the first strain gauge is grounded and through the series-connected second resistance strainer, the third and quarter resistors are connected to the inverting input of the second operational amplifier whose output through the fifth resistor is connected to its own inverting input through a large-scale amplifier connected to another input of the adder, the output to It is an output of the device, characterized in that, in order to increase accuracy by reducing the non-linearity of the conversion and the multiplicative component of the temperature error, it is provided with an additional adder, the first input of which is connected to the output of the power source, and the upstream side and a fourth resistor, a buffer amplifier, the input of which is connected to the connection point of the third resistor and the second resistance strain gauge. and the output with a non-inverting input of the second operational amplifier and the second input of an additional adder, and an additional large-scale amplifier whose input is connected to the output of the second operational amplifier, and the output with the third input of an additional adder.