SU1479882A1 - Digital extremal ac bridge - Google Patents

Abstract

The invention relates to electrical measuring equipment and is intended for use in AC bridges. The purpose of the invention is to increase the speed - by introducing a phase shifter, quadrature detector, key and two logical elements EXCLUSIVE OR, the set of functioning of which partially or completely eliminates the effect of changing the phase of the imbalance signal when passing through the minimum point and, as a result, increases the speed of measuring the complex resistive and conductive. 2 Il.

Description

The invention relates to electrical measuring technique and may find application in the construction of high-precision extreme AC bridges.

The purpose of the invention is to increase the measurement speed by reducing the duration of transients in the input selective stages of the extremum detector.

Fig. 1 shows a functional diagram of the proposed digital extremum AC bridge; Fig. 2 shows vector voltage diagrams at the output of a bridge measuring circuit and at the input of an extremum detector with a positive voltage unbalanced by an auxiliary (unregulated) parameter q.

2 and „0, and Up Re (UH) is a component of the voltage UH, respectively

imbalance in the regulated parameter p; II ,, Im (UH) is the component of the voltage Uh, corresponding to the imbalance in the parameter q. Point 0 corresponds to the equilibrium of the bridge measuring circuit. Points A, B, C and D correspond to modulation increments m -up, up, + other, -dr. The digital extremum AC bridge contains the first 1 and second 2 logic elements AND, five modulators 3–7 increments of the parameter p, respectively —D.r, + p, 0, –dr, + D flip-flop 8, reverse, one-oscillator 9, connected to the output of the clock generator 10. The direct and inverse outputs of the trigger 8 for the reverse are connected to one of the inputs of logic elements 1 and 2 and the inputs of modulators 3 and 7. The second inputs of elements 1 and 2 are connected to the direct output one-way (f

WITH

J J SS OS OS

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Rotor 9, the inverse output of which is connected to the input of the modulator 5. The inputs of the modulators 4 and 6 are connected respectively to the outputs of the elements 1 and 2. The outputs of the modulators 3-7 are connected to the inputs of the adder And, one of the inputs of which is also connected to the output divider 12 voltages The power generator 13 is connected to the input of the bridge measuring circuit 14, the second input of which is connected to the output of the adder 11, and its output is connected to the inputs of the phase shifter 15 and the key 16, the second input of which is connected to the output of the phase shifter 15, and the output to the input of the extremum detector G /. The control input of the extremum detector 17 is connected to the output of the clock generator 10, its output

enabled by potential 1 from the inverse output of the one-shot 9. In the excited state, the one-shot 9 turns on one of the modulators 4 or 6 (depending on the state of the trigger 8) and turns off the modulator 5. One of the modulators 3 and 7 controls triggered by the trigger 8 reverse, turned on constantly. JQ The modulation increments produced by modulators 3–7, respectively, are equal to &p; + dr -, 0; - & p + & p, with up being the adjustment steps, and & p - (2k + 1) steps.

5 Inclusion of modulation increments, m

+ UP1 modulators 3 and 7 are always opposite to the counting direction of the reversible counter 18 set by trigger 8 of the reverse. The modulation positive increments - to the countable 2Q of the same action + Lr (generated by the re-trigger trigger input 8, and the output of the blowout switches 4 and 6 during the actual increments - to the counter pulses of the one-shot 9, coincide to the input of the reversible counter 18 pulses, the output of which is connected to the input of the voltage divider 12. The input of the quadrature detector 19 is connected

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with the invoice direction. Therefore, for the duration of the action of the one-shot pulses, modulation effects are carried out in the prescribed direction, comprising (2k + 1) control steps. The amplitude and phase modulated signal imbalances the bridge frequency with the output of the bridge measuring circuit 14, and its reference input is with the output of the power supply generator 13. Output de

enabled by potential 1 from the inverse output of the one-shot 9. In the excited state, the one-shot 9 turns on one of the modulators 4 or 6 (depending on the state of the trigger 8) and turns off the modulator 5. One of the modulators 3 and 7 controls triggered by the trigger 8 reverse, turned on constantly. Q The modulation increments produced by modulators 3–7, respectively, are equal to &p; + dr -, 0; - & p + & p, with up being the adjustment steps, and & p - (2k + 1) steps.

5 Inclusion of modulation increments, m

+ UP1 modulators 3 and 7 are always opposite to the counting direction of the reversible counter 18 set by trigger 8 of the reverse. The modulation Q effects of + Lr (generated by modulators 4 and 6 during the action of the pulses of one-vibrator 9 coincide

+ UP1 modulators 3 and 7 are always opposite to the counting direction of the reversible counter 18 set by trigger 8 of the reverse. The modulation Q effects of + Lr (generated by modulators 4 and 6 during the action of the pulses of one-vibrator 9 coincide

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with the invoice direction. Therefore, for the duration of the action of the one-shot pulses, modulation effects are carried out in the prescribed direction, comprising (2k + 1) control steps. Modulated in amplitude and phase signal imbalance of the bridge circuit

the vector 19 is connected to one of the inputs JQ pi 14 through the phase shifter 15 and the key

the second element EXCLUSIVE OR 20, the second input of which is connected to the output of the first element EXCLUSIVE OR 21, and the output to the control input of the key 16. The inputs of the element 21 are connected to the direct outputs of the reverse trigger 8 and the one-shot 9. The outputs of the reverse trigger 8 are also connected to control inputs 18.

The device works as follows.

An alternating voltage or current is applied from the power supply generator 13 to the input of the measuring circuit 14, whereby a signal appears at the output of this circuit whose frequency coincides with the frequency of the generator, and the amplitude and phase are determined by the state of the modulators 3-7 and divider 12 tension The clock generator 10 periodically excites a single vibrator 9, which, together with the trigger 8, controls the operation of the modulators. If the one-shot is in the unexcited state (a logical zero signal at its direct output), then modulators 4 and 6 are turned off by potentials O from the outputs of elements I 1 and 2, and modulator 5

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16 or directly through the switch 16 enters an extremum detector 17, which determines the amplitude increments of the imbalance signal. The phase increments of this signal by an extremum detector according to the principle of its operation are not analyzed, therefore the presence of a phase shifter 15 and a key 16 does not disrupt the operation of the extremum detector, and only allows to reduce the duration of transients caused by modulation effects.

If the modulation increments in (2k + 1) control steps cause an increase in the amplitude of the imbalance signal, which indicates an incorrectly chosen control direction, then the extremum detector 17 forms a pulse at the output of positive increments, which is fed to the counting trigger input 8 of the reverse and Its state and the counting direction of the up / down counter are reversed. The following modulation increment, carried out in the opposite direction, causes a decrease in the amplitude of the signal imbalance and the appearance of impulse at the output of negative increments of the extremum detects

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0

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16 or directly through the switch 16 enters an extremum detector 17, which determines the amplitude increments of the imbalance signal. The phase increments of this signal by the extremum detector according to the principle of its operation are not analyzed, therefore the presence of the phase shifter 15 and the key 16 does not disrupt the operation of the extremum detector, and only allows to reduce the duration of transients caused by modulation effects.

If the modulation increments in (2k + 1) control steps cause an increase in the amplitude of the imbalance signal, which indicates an incorrectly chosen control direction, then the extremum detector 17 generates a pulse at the output of positive increments that goes to the counting trigger input 8 of the reverse and changes it The state and direction of the counting counter's counter to the opposite. The following modulation increment, carried out in the opposite direction, causes a decrease in the amplitude of the imbalance signal and the appearance of an impedance at the output of negative increments of the extremum detector.

torus 17, which is fed to the counting input of the reversible counter 18. The reversing pulse counter 18 controls the voltage divider 12, therefore changing the meter readings brings the measuring circuit 14 closer to the equilibrium state. Far from the equilibrium point on the steep portion of the parabolic dependence of the amplitude of the signal disequilibrium on the controlled parameter, the modulation effects in (2k + 1) steps cause very significant amplitude increments. The determination of the sign of these increments can be carried out accurately, irrespective of the phase distortions, and long before the end of the transient processes in the extremum detector 17. As we approach the equilibrium state, the amplitude increments decrease and the phase increments increase.

From the vector diagram (Fig. 2), the unbalance stresses at Uo. O it is seen that the modulation increment + Dp causes the transition of the end of the nonequilibrium signal vector from point A to point B, i.e rotation of this vector by an angle close to 9G, and a slight increment of its amplitude. In order to reliably estimate the sign of this increment, it is necessary that the transient processes in the extremum detector 17 are almost completed. If the vector of difference AB is supplied to the input of the extremum detector 17, as is the case in the device prototype, the duration of the transition process is quite significant. In the proposed device, due to the presence of the phase shifter 15, the quadrature detector 19, the key 16 and the EXCLUSIVE OR elements 20 and 21 simultaneously with the modulation effect, the imbalance signal vector is rotated by the angle 90 90 (transition from point B to point B). In fact, in the absence of modulation (signal O at the direct output of the one-shot 9) and the selected direction of control in the direction of increasing readings (signal 1 at the direct output of the trigger 8), signal 1 is present at the output of the element 21. The detector 19 is subject to an Id 0 (1) voltage. Element 20 operates as an inverter of the output signal of element 21. Signals 1 from the outputs of the first element EXCLUSIVE OR 21

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and the quadrature detector 19 is fed to the inputs of the second element EXCLUSIVE OR GO and set at its output the signal O, which with the help of a key 16 closes the output of the bridge measuring circuit 1D to the entrance of the extremum detector 17 (vektr OA). When excited one-shot 9 at the output

The Q of the first element 21 generates a signal O, and the output of the second element 20, a signal 1, which by means of a key 16 connects to the input of an extremum detector 12 an output of the phase switch 5 of the carrier 15 (vector, the difference vector is significantly reduced compared to the module AB and corresponds to one step regulation.

Q The change in the imbalance signal at the output of the measuring circuit 14 under the modulation effect - & p corresponds in the vector diagram to the transition from point C to T. D, However,

5 since prior to modulation (signals O on the direct outputs of the trigger 8 and the one-shot 9) the input of the extremum detector 17 is connected to the output of the phase shifter 15 (by signal 1

o from the output of element 20) and for the duration of this action its input is connected to the output of bridge circuit 14, then the change in signal corresponds to the transition from t. C (coincides with t. A) to t. D. Modulus of difference vector C1) in this case corresponds to one adjustment step.

When disequilibrium in the auxiliary (unregulated) parameter q,

.Q to the corresponding negative voltage U l 0, the output of the quadrature detector has a low level signal (O), therefore the EXCLUSIVE OR 20 element acts as a repeater of the output signal of the element 21. Now, with a modulation effect + another extremum detector input switches from the output of the phase shifter at the output of the measuring circuit, and when modulated by 0 i

- DR - in the opposite direction. The vector diagram presented in the second quadrant (Fig. 2) for the case U ,, 0 is repeated with U - 0 in the fourth quadrant, and the vector differences are also significantly reduced. In the proposed scheme, quadrature detector 19 determines only the sign of the imbalance signal by

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parameter q, which is also not one, but 5-7 or more control steps. Therefore, compared with the phase detectors of known bridges, the requirements for accuracy and stability of its operation here can be significantly reduced.

Let the increment of the amplitude of the disequilibrium signal corresponding to one step of adjustment be AU. Let us determine the duration t of the transient process in the electoral cascade of an extremum detector from the condition of 10–20% error.

We have

uUe

from where

 0.1-0.2AU,

t4 1.6-2.3.

Comparing the obtained value with the expression t of 3.9-5.3 Ј to the prototype, we see that the proposed technical solution makes it possible to reduce the duration of transients by about 2.5 times compared with the prototype.

The duration of the transient processes determines the choice of the pulse frequency of the clock generator (balancing rhythm) and, consequently, the measurement time. Therefore, we can conclude that the speed iz-. Measurements of the proposed digital extremal AC bridge, due to the introduction of a phase shifter, a key, a quadrature detector, and two logical elements EXCLUSIVE OR, are increased 2.5 times.

Claims (1)

Invention Formula Digital extremum AC bridge containing a power generator, a bridge measuring circuit, an extremum detector, the outputs of which are connected to the counting input of a reversible pulse counter and the input pack the reverse trigger, five modulators, the outputs of which are connected to the corresponding five inputs of the adder, the output of the adder is connected to the first input of the bridge measuring circuit, the second input of which is connected to the output of the power generator, the clock generator, the first output of which is connected to the first input of the extremum detector, the second - with the input of the one-vibration one, the inverse output of which is connected to the input of the first modulator, and the non-inverted output - with the first inputs of the first and second elements And, the second input of the first element And is connected with the input of the second modulator and the forward output of the reverse trigger, the inverse output of which is connected to the second input of the second element I and the input of the third modulator, a voltage divider whose input is connected to the output of the reversible counter, and the output to the sixth input of the adder, with In this case, the output of the first element I is connected to the input of the fourth modulator, and the output of the second element I is connected to the input of the fifth modulator, characterized in that, in order to increase the speed of measurements, a phase shifter, quadrature detector, key , the first and second elements EXCLUDE OR, the first and second inputs of the first of which are connected to the corresponding direct outputs of the reverse trigger and the one-oscillator, the output to the first input of the second element EXCLUSIVE OR, the output of which is connected to the control input of the key, and the second input - with the output of the quadrature detector, the reference input of which is connected to the output of the power generator, and the input to the output of the bridge measuring circuit, the first input of the key and the input of the phase shifter, the output of the phase shifter is connected to the second input of the key, the output of which th is connected to the second input of the extremum detector. 0 five five 0 five figure 1