SU1195262A1 - Apparatus for measuring resistance increment - Google Patents

Description

The invention relates to measuring equipment and can be applied when measuring the increment of the active resistance of resistive sensors. The purpose of the invention is to improve the measurement accuracy when the remote location of the measured resistor. The output of the integrator 1 is connected to the inverting input of the comparator unit 2. The output of the comparator unit 2 is connected to the input of the integrator 1, with the power supply diagonal of the resistive bridge (PM) 3, with the second output of the two-position key 5. The other power supply of the diagonal PM 3 is connected to the common bus devices. The outputs of the measuring diagonal of the PM 3 are connected to two inputs of the unbalance amplifier 4, the output of which is connected to the first output of the two-position switch 5. The input (moving contact) is connected to the inverting input of the comparator unit 2, the output of which is connected to the period meter 6. 2 Il.

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The invention relates to electrical measuring equipment and can be used in measuring the increment of the active resistance of resistive sensors, for example resistance thermocouples or strain gauges, on alternating current in the presence of a certain sensor capacitance and connecting line.

The purpose of the invention is to improve the measurement accuracy at the remote location of the measured resistor by reducing the nonlinearity of the conversion due to the capacitance of the communication line, leading to saturation of the unbalance amplifier during the transient process.

FIG. I shows the functional diagram of the proposed device; in fig. 2 - timing diagrams explaining the operation of the device ..

The device contains an integrator 1, unit 2 comparison, resistive bridge 3, the amplifier 4 unbalance, two-position key 5, the meter 6 period. The output of the integrator 1 is connected to the inverting input of the comparator unit 2, the output of which is connected to the input of the integrator 1, with the power supply diagonal of the resistive bridge 3, with the second output of the two-position key 5. Another power supply diagonal of the resistive bridge 3 is connected to the common bus device. The outputs of the measuring diagonal of the resistive bridge 3 are connected to two inputs of the unbalance amplifier 4, the output of which is connected to the first output of the two-position key 5, the input (moving contact) of which is connected to the inverting input of the comparator unit 2. The output of block 2 comparison is connected to the input of the meter 6 period.

The device works as follows.

The device performs frequency conversion with a change in the direction of integration in adjacent half-periods due to a change in the polarity of the output voltage of the comparator unit 2. Considered work. the device in the case where the two-position key 5 is in the position shown in FIG. 1. During operation, the linearly varying voltage from the output of the non-inverting integrator 1 (Fig. 2), which is the result of integrating the voltage coming from the output of the comparator 2 to the input of the integrator 1, enters the inverting input of the comparator 2. The end of the half-cycle of oscillations occurs at the moment when the voltage coming from the output of the integrator 1 to the input of the comparator unit 2 becomes equal to the voltage presently present at the non-inverting input of the comparator unit 2. Then unit 2 of the comparison at its output changes the polarity of the voltage of the center due to the overall positive feedback. This changes the sign of the steepness of the linearly varying voltage at the output of the integrator 1 and the processes are repeated until the next achievement of equality of the voltages at the input of the unit 2 of the comparison. Proceeding from the equality of the increments of the voltages at the inputs of the comparison unit 2., get the value of the period T-, the output oscillations of the device

T ₁ = 4'GpK £,. (one)

where ΐ 'is the time constant of integrator I;

P ~ integer, depending on the number of working arms of the resistive bridge 3;

K - gain transfer factor ^ 4 imbalance;

£ ^considers tionary change in the resistance increments of 4K * working shoulder bridge 3;

- the resistance value of the operating arm of bridge 3, when bridge 3 is balanced.

When translating the "movable" contact of the key 5 to the upper position (see Fig. I), when the input of the key 5 is connected to its second output, the output of the comparator 2 is connected to its non-inverting input, the process of forming the periods occurs as indicated. In this case, at the output of the unit 2 comparison, a period of natural oscillations of the device is formed.

T _g = 4C. (2)

The informative value is the ratio of the periods and.

(3)

2

and does not depend on the time constant

integrator.

In the diagram of FIG. 2, which presents to simplify the conditional case of instant key switching

3

Η 95262 4

5, the voltage and corresponds to the moments of switching the key 5, and the negative voltage ϋ _Γ corresponds to the position of the key 5 shown in FIG. 1, and positive - 5

switching key 5 to the second position when the output of the comparator unit 2 is connected to its non-inverting input. When switching the key 5, a transient process of establishing the period of the device output oscillation occurs, however, the time of the transition process does not exceed one or two periods of the device oscillations and practically does not reduce the speed of measurement 15. In the diagram (Fig. 2), the transition process ends in one period, located between the periods and. FIG. 2 conventionally depicted the case of the formation of 20

one period and which carries the measuring information. In practice, the number of generated periods η is determined by the periodicity of switching the key 5 and can be selected in accordance with the measurement requirements.

. With the remote location of the measured resistor connected to the device by the communication line, due to the line capacity at moments after the polarity is changed, the output of the comparison unit 2 causes a transient voltage setting on the resistive bridge, which can lead to saturation of the unbalance amplifier 4 (shown in the diagram of υθ of Fig. 2 by the dashed line 9, the voltage distortion at its output and the appearance of an error in nonlinearity during the measurement. However, if you choose the value of the minimum half-time duration yes output oscillations of the device so that by the end of this half-period the voltage at the output of the unbalance amplifier 4

established with the required accuracy relative to its true static value, the error due to the capacity of the communication line can be made quite insignificant and, as a result, it can be neglected.

The proposed device can be used to measure temperature increments with non-chamber pressure control methods based on pressure drop, the accuracy of which is largely determined by the accuracy of temperature increment measurement during the valid pause (from 1 to -10 hours), as the temperature increment causes a change pressure in a controlled object, not related to its tightness, and often exceeds the component due to the actual leakage.

Claims (1)

Claim A device for measuring the increment of resistance, containing an integrator, the output of which is connected to the first input of the comparator, the output of which is connected to the first vertex of the supply bridge diagonal of the resistive bridge, the second vertex of the supply diagonal is connected to the common bus of the device, and the tops of the bridge diagonal are connected to the unbalance amplifier inputs The output of which is connected to the first input of the on-off key, the second input of which is connected to the output of the comparison unit, a period meter, characterized in that In order to improve measurement accuracy, the integrator input is connected to the output of the comparison unit, the second input of which is connected to the output of the two-position key, and the input of the period meter is connected to the output of the comparison unit. 1195262