SU1629875A1 - Converter of complex impedance parameters - Google Patents

Abstract

The invention relates to a measuring and control technique and can be used in the construction of transducers of impedance parameters, for example, capacitive and inductive sensors. The converter contains a sinusoidal voltage generator 1, a convertible resistance 2, an operational amplifier 3, an exemplary element 4, a controlled voltage divider 5, a phase-sensitive indicator 6, resistors 7 and 8. The converter has an enhanced conversion accuracy due to a decrease in the error caused by the final magnitude of the gain of the amplifier. 1 il.

Description

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ABOUT

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The invention relates to a measuring and control technique and can be used in the construction of transducers of impedance parameters, for example, capacitive and inductive sensors.

The purpose of the invention is to improve the accuracy of conversion of the parameters of complex resistances, by reducing the error due to the finite value of the gain of the amplifier.

The drawing shows the functional diagram of the parameter converter of complex resistances.

The converter contains sinusoidal voltage generator 1, measured impedance 2, operational amplifier 3, model element 4, controlled voltage divider 5, phase-sensitive indicator 6, first and second resistors 7 and 8,

The output of the generator 1 through the converted complex resistance 2 is connected to the inverting input of the amplifier 3 and the first output of the reference element 4. The output of the amplifier 3 is connected to the input of the controlled voltage divider 5 and the first input of the phase-sensitive indicator b, the output of which is connected to the control input of the controlled divider 5 voltages Resistors 7 and 8, having equal values of resistance, are connected in series and connected between the output of amplifier 3 and the common bus, and their middle point is connected to the non-inverting input of amplifier 3. The output of controlled voltage divider 5 is connected to the second output of model element 4, the output of the generator 1 is connected to the second input of the phase-sensitive indicator b.

The Converter operates as follows.

The voltage Ui from the output of the generator 1 is fed through the measured impedance 2 to the input of amplifier 3, the output voltage 1) 2 of which is determined from the condition of equality of currents at the input of the amplifier and in the feedback circuit taking into account the equality of the values of resistors 7 and 8 :

u - (f + e)

Z0

0)

where Zx Rx + 1 / j w Cx; Z0 1 / j with Co; e -U2 / Ky;

Ku is the gain of the amplifier. After transformations we get

(-1+ - + tL- +

1. +

2 ZoKu ZQKu

I) - 2

Substitute instead of Zx, 0, we get

/ 3Z0

U2u - Ui U2p and 12-1-2Ku / 3-Ku1

(3)

where is ft

 Z

U2.

Zx + Zo U2p - real voltage value

This voltage is applied to the input of the phase-sensitive indicator 6, to another input of which the voltage Ui is supplied from the generator output. The output signal of the phase-sensitive indicator changes the division ratio of the controlled voltage dividers 5 until the quasi-equilibrium state between the input voltages of the phase-sensitive indicator is reached.

An expression for the transmission coefficient K of a controlled voltage divider

has the appearance

to -Cz (Ky-2)

Co So (Ku + 2

under Ku oo, we obtain Ki Cx / Co, where Kp and Ki are, respectively, real and ideal K. Substitute the expression for Kp in formula (3), we obtain

one

j ft Cx Rx

(“)

at Ku oo.

When Ku oo we have

U2n -2Ui

one

 co G Rx (5)

The value of the relative error in the parameter U2

yv2 U2P - U2n 2

U2n

-Kv - 2

(6)

55

The magnitude of the relative log in parameter K

 CR - Ki 4 Cx

K4

So (Ku + 2) Sh

For a known expression converter, the relative conversion errors are described as

X

(Qu + 1) 1 + KypV

(8) (9)

, L a - ° where PCX - g. g

LO t them

To improve the accuracy of the conversion, the modulus of the relative error of the converter, defined by expressions (6) and (7), should be less than the corresponding values for the known converter, defined by expressions (8) and (9). This effect is achieved when the condition

p. s 1 1,

With a known range of variation of the values of Cx with respect to C0, condition (10) can be satisfied by an appropriate choice of Co. which allows to increase the accuracy of the conversion by reducing the error due to the finite value

Ku

The converter also provides conversion of the parameters of the complex conductivity, while the complex conductance being converted must be connected between the amplifier input and the output of the controlled voltage divider, and

the model element is between the generator output and the amplifier input.

Claims (1)

Claims of the Inverter of complex resistance parameters, comprising a sinusoidal voltage generator, an exemplary element, a controlled voltage divider, a phase-sensitive indicator, an operational amplifier. 10 an inverting input of which is connected to the first output of the reference element directly and through a convertible resistance to the output of a sinusoidal voltage generator, and the output of an operational amplifier is connected to the input of a controlled voltage divider and the first input of a phase-sensitive indicator, the output of which is connected to a controlled input of divide by 20 liters of voltage, which is characterized by the fact that, in order to increase accuracy by (Yu) reducing the error due to the final magnitude of the gain of the amplifier, entered into the converter 25, the first and second resistors having equal resistance values, the first terminals of the resistors respectively being connected to the output of the operational amplifier and the common bus, and the second terminals 30 are connected and connected to the non-inverting input of the operational amplifier, the output of the controlled voltage divider is connected to the second output of the reference element, the output of the generator is connected to the second input of the phase-sensitive indicator.