SU1495718A1 - Device for measuring resistance increment - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure the increment in active resistance of resistors and resistive sensors connected via long lines of communication, such as strain gages, resistance thermometers and resistors, during their manufacture. The aim of the invention is to improve the speed of the device. The device contains two switches 1 and 13, a reference resistor 2 with an average output, a current source 3, keys 4 and 15, a resistive sensor 5, a differential amplifier 6, a synchronization unit 7, a comparison unit 8, an integrator 9 made on the basis of an operational amplifier 10, the capacitor 11 of the resistor 12 and the multiplexer 14. This device provides a higher measurement accuracy compared to the prototype, since it lacks an amplifier that introduces errors in the prototype from the instability of the transfer coefficients and the drift its voltage offset no. 2 Il.

Description

U, (t) U (t,). (iil rbRAryiizKliI o R.,

(four)

where t е (,), t ,.

At time t j, the voltage between the capacitor plates. 11 doi (..-, - .- -K + lc: K-ItR,.

UcV.c,

-3 - t 2loRAK ± IolRj

At time t

compensation 1. At the same time at time t, the same changes occur at the time t, as indicated by the synchronization node signals, as at time t ,.

It is obvious that For an arbitrary number - h correction cycles with simultaneous integration of the signal of the resistive sensor 5 with a duration, tg-t at the moment of the end of the last (the time t in Fig. 2, between the plates of the capacitor 11 will be present

and (t) l2siu A5- ± -Si5--5i. X

With (

-2loRAK + lo Ra T - - Thus, the integration of the input signal during a fixed interval tg-t, T is carried out without missing information.

I

At time t, the signal of synchronization unit 7 opens the second key 15, closes the first key 4, returns the first 1 and second 13 switches to the position shown in Fig. 1, and its third input is connected to Bbixoj y of the multiplexer 14. As a result, the voltage 1 R, which is present on the average output of the reference resistor 2, is connected to the noninverting input of the operative (taking into account expression (2))

about

(five)

25

thirty

/ 35

40

Q of the sig- nal amplifier 10 and to the second input of the comparator unit 8, the output of the integrator 9, and consequently, at the first input of the comparator unit 8, there is a voltage

Uu (t6 Uc (t,) +

 .bRz T

 four . V /)

Starting from the moment of time t ,, the voltage at the output of the integrator 9 increases linearly until the moment of equality to the voltage present at the second input of the comparison unit 8. The change in voltage at the output of the integrator 9 in the interval t ,, - tg is described by the expression

U, (t) U, (t,) ,, p. (eight) ,

and at the moment of compiling the block 8 of comparison there is equality

"((T,) | (t8-te) + IoR

IoR2cp.

gsr- (9)

Taking into account (6), expression (9) can be represented as

(e-t6) - V --- ° ---- | - (o)

Resistance of resistive sensor 5 corresponds to the expression

  Ao

(eleven)

where R. is the initial resistance

resistive sensor; AR measured resistance increment of the resistive sensor,

Taking this into account, equality (10) can be

convert to mind

rt- -t-. -

-L V -o VO T

K R

UR6

BUT; 2

R

}

(12)

take R,

(13)

 Ri KRAO 2 2 and after obvious conversions from expression (10) we get

te) --H

T ARA- -T.

R

Ac

(14)

The left part of equality (14) constitutes the informative interval, denoting it by T ,,, from equality (14) we obtain the final expression of the device conversion function

.PC

fltix

R "

(15)

Ao

From this it follows that the proposed

the device produces the same result as the known device with the duration of the conversion cycle

 | | | h-T 1.5. T,

In the known device, the conversion cycle time is 2T.

Thus, the speed of the proposed device is 1.3 times higher than that of the known device by eliminating information gaps when integrating the signal of the resistive sensor 5 during a fixed interval t - t T.

At the same time, the sensitivity of the known device is completely preserved and there is no amplifier contributing to the known device errors from the instability of the transmission coefficients and the drift of its bias voltage. Sly, this device is also more accurate.

To determine the sign of the deviation of the measured resistance increment jRi from the initial value Rd, it is sufficient to establish the temporary position

0

five

0

five

thirty

35

dd

50

55

Kie informative interval T C ,,, relative to the middle of a fixed interval T (time t in Fig. 2): if it ends at time t - increment counts. is negative if T d ,, begins at time t — the increment is considered positive. The sign information is removed from the second information output of the synchronization unit 7.

Claims (1)

Formula IZ A resistor increment measuring device DO containing a current source, the output of which through the first switch is connected to the first current output of a resistive sensor, the potential outputs of which are connected to the inputs of a differential amplifier, a reference resistor with an average output connected to the first output of the common bus, a synchronization unit , the first control output of which is connected to the control input of the first key, the second control output of the synchronization unit is connected to the control input of the first switch, the output of which is It is connected via an integrator consisting of an operational amplifier, a resistor and a capacitor, which is connected between the output and the inverting input of the operational amplifier, to the inverting input of the latter connected the first output of the resistor, the second output of which is the integrator input, with the first input of the comparison unit, the output which is connected to the input of the synchronization unit, the first information output of the synchronization unit is the sign output, the second information output is the device output, characterized in that in order to increase speed, a multiplexer, a second switch and a second key are entered into it, the second key input is connected to the current source, the output is from the second current output of the resistive sensor and the second input of the second switch, the first input of which is connected to the first current output of the resistive sensor, the output of the second switch is connected to the second output of the reference resistor and the second information input of the multiplexer. 914957 the middle pin of the reference resistor is connected to the third information input of the multiplexer, the first information input of which is connected to the output, the differential amplifier and the second input of the first switch, the first input of the first switch is connected to the common bus, the output of the multiplexer is connected to the non-inverting input of the integrator operational amplifier and with the second entrance 18-- Oh Comparison unit, second control-; rd output of synchronization unit; with the control input of the second switch and the first control input of the multiplexer, the third control output of the block with synchronization is connected to the second control input of the multiplexer, and the fourth control output of the synchronization block is connected with the second input of