SU1281874A1 - Strain-measuring device - Google Patents

Abstract

The invention can be used to measure strain. The purpose of the invention is to increase measurement accuracy. The strain gauge 1 is made in the form of a four-shoulder bridge. Matching unit 2 includes pre-3 and output 4 amplifiers. In addition, the device contains a recorder 5, keys 7, 9 and 12, a sampling and storage circuit 8, a generator 10, a driver I1 of calibration pulses, a calibration resistor 15. Introduction to the device of a compensating amplifier 6, keys 13 and 14, calibration resistors 16 and 17 allows you to improve the accuracy of compensation of the input signal ;; of a new signal and eliminate the influence of the degree of deformation of the strain gauge on the magnitude of the calibration signal. This reduces visibility during calibration. 1 3.pl-ly, 2 ill. § (L

Description

figure 1

1 I

This invention relates to a measurement technique and can be used to measure deformation.

The purpose of the invention is to improve the measurement accuracy by reducing the calibration errors.

Figure 1 presents the block diagram of the device; Fig. 2 shows graphs of the voltage at the outputs of the device blocks.

The strain gauge device contains a series-connected strain gauge 1, made in the form of a four-arm bridge, a matching unit 2, made in the form of a series-connected preamplifier 3 and an output amplifier 4, a register 5, a compensating amplifier 6, the input of which is connected to the output of a matching unit 2, and the output through the first key 7 is connected to the input of the sampling and storage circuit 8, the output of which is connected via the second key 9 to the second input of the output amplifier 4, connected in series with the generator O and forming 11 calibration pulses, the outputs of which are connected to the control inputs of keys 7, 9, 12, 13 and 14, calibration resistors: the first calibration resistor 15 is connected between the second peak of the supply diagonal and the second shoulder of the strain gauge, to the terminals of the first calibration resistor 15 under - the input and output of the third key 12 are turned on, the second calibration resistor 16 is connected in series with the third shoulder resistor, the input and output of the fourth key 13 are connected to the terminals of the second calibration resistor 16, the third calibration resistor 17 connected in series between the power bus and the first vertex of the power diagonal of the strain gauge, the input and output of the fifth key 14 are connected to the terminals of the third calibration resistor 17.

The device works as follows.

The load cell converts mechanical oscillations into an electrical signal that amplifies matching unit 2 at the command of generator 10 shaper 11 calibration pulses changes the state of load cell 1 so that it returns a signal to a predetermined calibration level.

In the mode of recording information about the process being measured, the key 7 is closed and the circuit 8 of sampling and storage is memorized.

This signal comes from the output of the compensating amplifier 6, but since the switch 9 is open at this time, the signal from the sampling and storage circuit 8 does not come to the input of the output amplifier 4 (figure 2, diagram 4, interval O - t). In the recording mode of the process being measured, the keys 12 and 13 are closed, and the key 14 is open. In this mode, the calibration w resistors 15 and 16 are shorted. At time t (FIG. 2, diagram I), on command from the driver I1 of the calibration pulses, the switch 9 closes and the auto-compensation circuit 15 starts working, the output from the matching unit 2 arrives at the input of the compensating amplifier 6, from its output to the input of the sampling circuit 8 and storage and from the output of the latter to the second 20 input of the output amplifier 4.

The operation of cJteM is described by the following equations:

25

thirty

35

Ubb, x., (Ub .. -U bu-cS K / Kg). (1) where ,, g is the output voltage of the output amplifier; K - transfer coefficient output.amplifier; Ugxf input voltage from the preamplifier output to the first input of the output amplifier;

K - transfer coefficient of the compensating amplifier; K is the transmission coefficient of the sampling and storage scheme. Transforming equation (1), semi

 , g.

1 + K K, Kb

(2)

Analysis of the equation (.2) allows

45 to conclude that with a finite value of K, Ug (, ix.c & O with K - Co J, i.e., with a sufficiently large transfer coefficient of the compensating amplifier (), therefore, 50 is the change in the compensation circuit of the input the signal allows to eliminate measurement errors

known device, since there is no need for an exact selection of the number 55 of the chain transfer factors

connection and output amplifier.

Virtually no effect on the accuracy of the zero setting on the output

matching block do not have temperature and time drifts.

At time t, the signal from the imaging unit 11 of the calibration pulses opens the key 7 (diagram 2). The value stored in the sampling and storage scheme is still fed to the second input of the output, amplifier 4, maintaining at its output

ivyh y 0.

At time t (diagram 3), the third output of the driver 11 of the calibration pulses sends a signal to the control inputs of the keys 12 and 13, their opening, and to the control input of the key 14, to close it. At this point in time, the calibration level is formed.

The operation of the circuit at this moment is described by the following expressions. Let be

R ,,

a R

t

one

one

- KJ 2 ki 2

where R, R, R ,, R is the resistance of the corresponding shoulder of the tensome bridge; R - calibration resistance

n - coefficient;

aR - the magnitude of the changes in resistance of the strain gauges; k - coefficient.

In the recording mode of the process being measured, the keys 12 and 13 are closed, the key 14 is open, then

and

di

- and

Uh

ftbix co

 2 + n

TO,

where K is the gain factor of the matching unit; K K K,

at t 2

and . - output voltage according to (floating block;

K - preamp amplifier transfer ratio; Kj is the gain of the output amplifier. To maximize the calculations, then Uj ,,,.,., Where and, 7 is the voltage at the output of the output amplifier and K, -Ki.

& calibration mode keys 12 and 13 open, and the key 14 closes, then

and.

- Fa.

n + 2k 2 + n

At the output of the amplifier, a calibration signal U .. ,,., Appears.

and.

 F. k, -n 2 + n

Analysis of the expression shows that the value of the calibration signal does not depend on the degree of deformation of the shadow bridge {there is no coefficient -, uR in the expression

1 i 1 The factor k 1 At time t, key 14 is opened and keys 12 and 13 are closed (diagram 3). At time t e,

key 9 opens (diagram 1), at time t the key 7 closes (diagram 2). After the moment of time t, the circuit is transferred to the mode of recording information about the measured value

(chart 4).

The time division of key firing is introduced in order to eliminate the effect of transients on the recorded information.

Thus, this strain gauge device allows one to increase the accuracy of the input signal compensation and to eliminate the influence of the strain rate of the strain gauge on the magnitude of the calibration signal, which makes it possible to increase the measurement accuracy.

Claims (2)

1. Strain gauge device containing sequentially connected four-pin strainer, matching unit, recorder, as well as serially connected generator and shaper of calibration pulses, sampling and storage circuit, three keys, the first of which is connected to the input of the sampling and storage circuit, whose output is connected to the input of the second key, output whom connected to the second input of the matching unit, and the control inputs of the keys are connected to the corresponding outputs of the driver of calibration pulses, the first calibration resistor, characterized in that, in order to improve measurement accuracy by reducing disturbances during calibration, the second and third calibration resistors, a compensating amplifier, the fourth and fifth keys, the control inputs of which are connected to the third output of the driver of the calibration pulses, and the input and output of the fourth key are connected respectively, the outputs of the second calibration resistor connected in series with the resistor of the third arm of the tenzomost, the input and output of the fifth key are connected respectively to the leads of the third calibration resistor connected between the power rail and the first vertex of the diagonal of the strainer bridge; the pins of the first calibration resistor connected between the second The power supply diagonal busbar and the resistor of the second shoulder of the tensometer bridge, the input of the compensating amplifier is connected to the output of the matching unit, and the output is connected to the input of the first key. 2. The device according to claim 1, that is, that the value of the second calibration resistor is chosen equal to the value of the first calibration resistor, and the value of the third calibration resistor is equal to half the first calibration resistor. .t, Utsts FIG. 2