SU608103A1 - Digital bridge for measuring capacitance and loss angle tangent of capacitors - Google Patents

Description

(54) DIGITAL BRIDGE FOR MEASURING CAPACITY AND TANGENSE ANGLE OF LOSS OF CAPACITORS

alternating voltage generator included in the diagonal of the power supply of the bridge measuring circuit, the zero-organ connected at the output of the bridge measuring circuit, threshold circuits, the control unit and the reading device, are equipped with two switches, three differentiating stages, two key circuits, two gate drivers , the driver of the reference voltage, two registers, and one of the switches is connected between the quadrupole and the operational amplifiers of the bridge measuring circuit and the inputs zero -organ, the control input of which is connected to the control unit, which is connected to the registers, and the output is connected to the inputs of the threshold circuits, while one of the inputs of the first threshold circuit is connected to the output of the zero-organ through one differentiating cascade, and the other input is the same threshold of the circuit is connected to the output of one of the operational amplifiers of the bridge measuring circuit and through another differential cascade and one of the gate-pulse drivers with the second switch, the other input of the second threshold circuit through the driver of the supports voltage and the third differential cascade is connected to a voltage generator, the outputs of both threshold circuits are connected via key circuits to registers whose outputs are connected to the inputs of a reading device, and the control input of one of the key circuits is connected to a voltage generator through another gate driver pulses and the second switch, and the control input of another threshold circuit. - with the same switch.

FIG. I given the scheme of the proposed device; in fig. 2 - diagrams on the operation of the device.

The device contains a measuring bridge I, a voltage generator 2, the measured impedance 3 (Cx and tg6x), operational amplifiers 4 and 5, covered by deep negative feedback, the output voltage of which is proportional to the current through the measured impedance and drop, respectively tension on it; a quadrupole 6 with an adjustable transfer ratio equal to (1) for a parallel replacement circuit and (1-f) for a serial replacement circuit for a measured capacitor, where K is a coefficient that is adjustable when balancing tg6; exemplary measures for testing the capacitive component of the complex resistance (CS) 7; differentiating cascade 8, shaper 9 of the reference voltage (BACKGROUND) threshold circuit capacity; differential cascade 10; And, 12 strobe pulses (VLF) formers, which form short pulses at the moment of zero amlititude. sinusoidal voltage supplied to the input of the VIF, switch i3, zero-organ (IO) 14, voltage comparator 15, amplifier 16 with 1stable-adjustable coefficient (gain factor; threshold circuits 17 .18 (PS) respectively in tg6 and C; key circuit 19, differentiating cascade 20, key circuit 21, decade registers 22, 23, respectively, according to tgfi and C. The number of decades is determined by the number of digits in the mantissa of reference in C and tg6, the control unit 24, which synchronizes and controls the operation of the device , digital reading device 25.

FIG. 2a explains the operation of the proposed device for. sequential capacitor replacement circuit, where

Y is the voltage at the output of the amplifier 4;

Oil - at the exit of the quadrupole 6 when adjusted for tg6;

Oz - at the output of the amplifier 5 when adjusting for capacity;

AU |, AU2 - at the input of the comparator 15, respectively, before adjusting the scales in C and tgS and after the first adjustment;

do Oie g - at the output of the differentiating cascade 10;

LO (о Л0 | е2 - at the output of differentiating cascade 20;

02 at the output of the imager 9;

0, e is the projection of the voltage imbalance vector prior to the commencement of balancing on the axis 0, -e; F;

{Jif capacitive component of unbalance voltage vector prior to balancing;

 - the vector of the capacitive component of the voltage on the measured capacitor, equal in magnitude to the unit of the reference voltage in capacitance;

Олв, Оаэ - vectors of the active component of the voltage unbalance before the start of equilibration for different replacement circuits of the capacitor;

Ol "- - voltage" Oah, shifted by

angle | -.,

RojwCx

, and, -Oo

l - + - jt§Sx

amplifier output voltage 4.

At the output of the quadrupole b voltage -

) -0, i () (О

It can be seen from equation (1) that when adjusting the circuit in tgS by changing the coefficient K, the end of the vector Otz moves along straight lines (see Fig. 2, a).

The output voltage of the amplifier 5 0, -Ooj.wRjC, fl)

Claims (1)

It can be seen from equation (2) that the end of the vector Oz also moves along a straight OK when balancing the circuit in terms of capacity. Thus, the vector, the voltage unbalance at the input of the comparator 15 when adjusting and With one end moves along the direct axis, and the other along the OK. Because of this, the projection of the voltage unbalance vector LO | or AOj on the direct ae, referred to the reference voltage Uee, uniquely determines the magnitude of the unbalance of the measuring bridge by tg6, and the projection of the vector of the unbalance voltage on the forward OK, referred to the projection of the vector of the reference voltage Oa on the same forward, uniquely determines the magnitude of the unbalance of the bridge in capacity. For a parallel replacement circuit (see Fig. 2.6), when the switches are in the opposite state, the voltage is O, -poRojwCx (l jtg6x) - (3) Uu, C, (l-jwK) (4) As can be seen from equations (3) and (4), one end of the unbalance voltage vector is stationary (point a), and the other moves when the circuit is adjusted along tg6 along a straight line parallel to Au when adjusted along the capacitance along a straight line parallel to OK. As a result, the projection of the voltage imbalance vector on the direct parallel to AB, and referred to the reference voltage, uniquely determines the value tg6, and the projection of the same vector to the direct parallel OK, related to the vector of the reference voltage Ua, uniquely determined em capacity value. Estimation of the capacitance value for a sequential replacement circuit of a capacitor by f-P 12. At Xu O, at the output of the FSI 12 a strobe pulse appears, opening the key circuit 21 in terms of capacity. The value of tg6 is estimated at the moment of time generated by the strobe pulse shaper 11. At DO O, a strobe pulse appears at the output of the strobe pulse shaper 11, opening the key circuit 19 by tg6 {and the key circuit 2 by capacitance with an parallel replacement circuit ). The process of equalizing capacitance is reduced to measuring the magnitude of the vector O (relative to the magnitude of the vector 0 ", i.e., the operation of dividing the voltage proportional to the current through the capacitance (0 |), the value of the voltage drop across the capacitive component and connecting the corresponding weights in terms of capacity. The process of uuroviva and in tg6 -svb is for evaluating the vector Cte for Uj, or for the vector Оа. for Uee, i.e. d | tg6 -, and connecting the corresponding weights for tgfi. Indicated division operations for each digit of the mantissa in C and tgd pro at the moment when Oy 0, the reference voltage vector tJ is equal to lOalcosfi LOlOol cos6 lOOoj. At the same time, the voltage input D0 | comes to the signal input of the threshold circuit 18. The resulting knockout of the threshold circuit at the coefficient usi The N-O value, equal to I, determines the digital value of the capacitance in the first discharge and is stored in the 1st decade of the register 23 in capacity. At the time when DO О, and О О turns out to be equal in value | Ivv} and on the signal the input of the PS along tgft 17 is equal to oEI, where the voltage Oeti is turned on a 90 ° voltage Oae: Thus o6razol; The threshold circuit 17 shows the ratio of the two voltages jOoef / fOae; i.e., with a unit gain of H-O, the first digit is read by tg6. The result of the comparison is stored in the 1st decade of the register 22. After obtaining the result of the comparison in C and tg6, the control unit issues a command to simultaneously connect the corresponding weights in the first discharge in C and tg6, and also increases the gain factor H-O by 10 times. At the same time, the next clock cycle begins, at the end of which, the value of the 2nd digit of C and tg6 is produced by the magnitude of the imbalance signal. Let, for example, after the 1-g clock cycle, input voltage A02 is applied to the input I – O. which, oh is the difference of two voltages, ohm and us. The component of the vector DOG, equal to o, corresponds to the residual capacitive component. It is determined by comparing the 10 times amplified signal AUj with the Cr vector at time and 10, 0. As a result, a 2-digit capacity is determined. The component pn of the vector DO2 characterizes-FSB. in “and,„ „y-Ggb JcSlein 10 times the length pp (at the output of the key circuit 19 shifted by 90 °) is compared using the threshold circuit again with the voltage Soe (at the time Oo 0) and, in terms of Uoe, the threshold scheme The 2nd digit tg6, etc. are possible. When switching with the help of a threshold circuit, the weighting error on C and tg6 are excluded by methods known for direct balancing. The process of measuring C and tgfi with a parallel replacement scheme differs from the sequence in that the determination of digits by capacitance and tg6 occurs at the same time when Oo O. At this time, the threshold circuit is determined by capacitance 11, and the threshold scheme for tg6-, where Ug lOOoe-J. When using the proposed bridge to measure capacitance, it is possible to use the direct method of balancing and simultaneously switching weights along C and tgfi for two capacitor replacement circuits, which ensures high speed of the device. A digital bridge for measuring the capacitance and loss tangent of capacitors, comprising a bridge measuring circuit, an alternating voltage generator included in the diagonal of the power supply of the bridge measuring circuit, a zero-body connected at the output of the bridge measuring circuit, threshold circuits, a control unit and a readout device, characterized in that, in order to improve speed for both parallel and post