SU1413536A1 - Automatic digital a.c. bridge - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to measure one of the components of the impedance or conductivity. Digital automatic bridge (TSAI) - alternating current contains a generator I supply, transformer 2 voltage with primary and secondary windings 3 and 4.5, respectively, common comparator bus 7 currents with indicator and auxiliary windings 8 and 9-11, respectively, control unit 14 , model measure 13 of capacitance, transducer 16 code - conductivity, measurement object 12, discrete functional transducer 15. TsAM has a high measurement accuracy by increasing the accuracy of compensation of an unmeasurable parameter. 1 z.p, f-ly, 2 ill. i (Л С

Description

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The invention relates to electrical measuring equipment and is intended to measure one of the components of the impedance or conductivity.

The purpose of the invention is to increase the measurement accuracy by increasing the accuracy of compensation of an unmeasurable parameter.

FIG. 1 is a block diagram of a digital automatic AC bridge; in fig. 2 - vector diagram explaining the balancing process,.

The digital automatic AC bridge contains a power generator 1, a transformer 2 with a primary voltage 3 and secondary 4 and 5 windings, a balancing unit 6, a 7-current comparator with indicator 8 and auxiliary.: 9-11 windings, a measurement object 12, exemplary capacity measure 13, control unit 14 (phase converter - code), discrete function converter 15 and converter 16 - code - conductivity.

The generator 1 is connected to the primary winding 3 of the transformer 2 voltage and feeds the pavement measuring circuit. The secondary windings 4 and 5 of the transformer 2 voltage are connected to the corresponding elements 12, 13 and 16. The currents through these elements are compared in the comparator 7 currents. According to the signals taken from the indicator winding 8, the balancing unit 6 changes the number of turns of the adjustable secondary winding 5 of the voltage transformer 2 and balances the bridge measuring circuit according to the measured differential (capacitance C) of the object 12 measuring Digital An automatic AC bridge works as follows.

At the moment of equilibrium of the bridge-measuring circuit between the measured component C of the conductivity of the object 12 and the number of turns rij of the adjustable secondary winding 5, the following relationship exists:

ms p, o., p y; ::. V

GO4 PD

(ABOUT

where m is the number of turns of the secondary winding 4;

PdIp - the number of turns of the auxiliary windings 9 and 10, respectively;

Co is the value of the capacity of the model measure 13.

The current I through the measurement object 12 is composed of two components — capacitive {measured) 1, directed at an angle of 90 to the voltage vector Uf. generator 1, and active (unchangeable) 1, in phase with and (Fig. 2), the presence of an immeasurable component will interfere with balancing the bridge measuring circuit according to the measured parameter Cj (. To compensate for the current In with an immeasurable component q, consisting of a block 14, a discrete functional converter 15, a converter 16 and the auxiliary winding 11 of the comparator 7 currents.

The current 1 flowing through the measurement object 12 is fed to the input of the control unit 4, in which the phase shift Ч of this current is converted relative to the phase PJ. voltage generator 1 to code N ,:

K, (f, -Ч,) K, f, (2)

where K is the proportionality coefficient.

From the output of the block .14, the code N, is fed to the input of the discrete function converter 15, in which the code N. is converted by the formula

Wj ,,, (% - (3)

where Kj is the proportionality coefficient.

35 40. - 45

Q

55

From the output of the discrete functional converter 15, the Ng code is fed to the control inputs of the converter 16, the code is the conductivity, and it regulates the conductivity of the converter 16, and hence the current 1m flowing through it. The current I through the converter 16 is also regulated by switching the number of turns of the winding 5 (by changing the output voltage and the winding 5) of the voltage transformer 2. In this case, the current 1 through the converter 16 is determined by the expression

f, KU5.q.N, K, -U, .q.K., (4 ..

- j (4)

where K is the proportionality coefficient;

q is the discrete change in the conductivity of the converter 16. In turn, the current through the standard measure 13 of capacitance

Uj.

The values of the coefficients K, K, and K are chosen such that when the bridge circuit is equilibrium with respect to the measured component C, the current I is equal to the current 1, the unmeasured component q.

Current 1. flows through the auxiliary winding 11 of the comparator 7 currents applied to the core of the comparator 7 oppositely relative to the winding 9, as a result of which the magnetic fluxes of these windings are subtracted (compensated) and the presence of the non-measurable component q of the complex-conductivity of the object 12 (presence of the component TD the winding 9 of the comparator 7) will not interfere with the balancing of the bridge circuit (will not reduce the sensitivity of the bridge circuit near the equilibrium point) according to the measured parameter Su.

The process of balancing a bridge circuit can be reflected in a vector diagram (Fig. 2) in the complex plane W. Point C denotes the end of the century. torus I, fixed in the process of balancing, with a point c, is the end of the balancing vector lo + ij. With 35 adjusting the length of vector I, collinear to vector 1,, and the fulfillment of equality (4), the end of vector I - –u (point c) will move along ten percent fractions. The error of the transducer 15 is determined by the deviation of the used approximating polynomial (approximation function) from the real function and can be practically reduced to the tenths and hundredths of a percent. The 16-code-conductivity-to-digital-to-analog converter (DAC) error is the sum of the non-linearity and conversion factor errors, which are no more than hundredths of a percent for DACs with resistive dividers and no more than thousand fractions of percent dp DACs with inductive dividers , and methodological error - the quantization error of the output signal of the DAC (quantization error of the active conductivity value of the converter 16), the size of which can be adjusted depending on tr Expected accuracy (discreteness) of adjusting the output signal of the DAC (i.e., depending on the accuracy of the adjustment of the active conductivity of the converter 16).

25

Claims (2)

30 claims 1, a digital automatic ac bridge containing a power generator, a voltage transformer, one output of the primary winding of which is connected to the first output of the power generator and the other with a common bus, the ends of the adjustable and unregulated secondary windings of the transformer 1. The voltage balance bridge of the torus 40 wives are connected to a common bus, current comparator, the indicator winding of which is connected to the corresponding # 1 inputs of the balancing unit, the start of the unregulated secondary-immeasurable component of the voltage transformer will be right. As can be seen from the diagram, at the moment of equilibrium of the pavement of the circuit according to the measured parameter C .. (), the compensating current 1 will be equal to current IQ Sasha through the terminals for connecting the measurement object is connected to the beginning of the first auxiliary winding of the current comparator, the end of which is connected to the first input of the control unit, the second input of which is connected to the second output of the power generator, the beginning of the second and third auxiliary windings of the current comparator are connected to the common bus, the end of the second auxiliary The windings of the current comparator are connected to the control panel via a reference capacitance measure, and their input by the number switch. turns of the adjustable secondary winding1 ") are subtracted (compensate In the comparator 7 currents, these currents (1. and c). The control unit 14 can be built on the basis of the counter count of quantizing pulses for the time interval between the moments of the leading or trailing edges of the sinusoids of the current L and the voltage U within one period. The error of block 14 with this conversion may be no more than ten 14135364 tenths of a percent. The error of the transducer 15 is determined by the deviation of the approximating polynomial used (approximation function) from the real function and can be practically reduced to the percent, hundredths and hundredths. The error of the 16-code-conductivity-digital-to-analog converter (DAC) converter is made up of non-linearity and conversion factor errors, which are no more than hundredths of a percent for DACs with resistive dividers and no more than thousandths of percent dp of a DAC with inductive dividers, and methodical error — the quantization error of the output signal of the DAC (the quantization error of the active conductivity value of the converter 16), the size of which can be set depending on required accuracy (discreteness) of adjusting the output signal of the DAC (i.e., depending on the accuracy of adjusting the active conductivity of the converter 16). 15 20 25 . 35 30 claims 1, Digital automatic ac bridge containing a power generator, a voltage transformer, one output of the primary winding of which is connected to the first output of the power generator, and the other with a common bus, the ends of the adjustable and unregulated secondary windings of the transformer0 through the terminals for connecting the measurement object is connected to the beginning of the first auxiliary winding of the current comparator, the end of which is connected to the first input of the control unit, the second input of which is connected to the second output of the power generator, the beginning of the second and third auxiliary windings of the current comparator are connected to the common bus, the end of the second auxiliary The windings of the current comparator are connected to the control panel via a reference capacitance measure, and their input by the number switch. turns of the adjustable secondary winding5U13536 voltage transformer and with the output of the balancing unit, and the end of the third auxiliary winding of the current comparator is connected to the first output, the transducer's code - conductivity, which contributes so that, in order to improve the measurement accuracy, a discrete functional the converter, the inputs of which are connected to the corresponding outputs of the control unit, and the outputs - to the corresponding inputs of the converter of the converter; the code is the conductivity, the second output of which is connected to the control switching input of numbers turns adjustable transformer secondary voltage 2. The device according to claim 1, characterized in that the control unit is made in the form of a phase-code converter. X