RU1830492C - Capacious transformation of sensors into voltage - Google Patents

Abstract

The invention relates to electrical engineering and can be used to convert parameters of sensors with capacitive equivalent circuitry. In order to increase accuracy, two resistors and an additional error compensation gain circuit are added to it. 1 ill.

Description

The invention relates to an electrical measuring technique, namely, the conversion of the informative parameter of a capacitive sensor, and can be used to convert the informative parameter of various sensors to voltage.

An object of the invention is to increase the accuracy of converting a sensor capacitance to voltage.

The drawing shows a functional diagram of a transducer of a sensor capacitance to voltage.

It consists of generator 1, convertible 2 (Cx) and model 3 (Co) capacities; the first 4, second 5, third 6, fourth 7, fifth 8 and sixth 9 resistors; first 10 and second 11 amplifiers.

The converter operates as follows.

The voltage from the output of the generator 1 is supplied through the converted capacitance 2 to the non-inverting input of the first operational amplifier 10. The output voltage Tsg of the converter will be determined based on two equations: the initial equation for the first amplifier, found by the well-known formula:

e + -

U

out

(1)

will look like this:

Uo j 0 Cx +. Uo j (Oh.

1

 O) Cx + j (O Co +

Re

"

fe

Ui iRi + U2I R4 Ui

1 KUG

Ri T R4 Rs

(2)

and the expression for the output voltage LJ2 of the second amplifier 8 will be described by the following known expression:

U2 -Ui

By

1

R2

1 +

R3

Kua

C + YY)

00

with

g

H)

to

where from:

. "G- TB- + TYA-X1 + - -)"

Substituted equation (3) in (2), we get:

Wojft) Cx -4-WojfwCo

U2

R3

G1. 1 / L .. kz -i

 VR2) J

jft) Cx + j «Co + 1 Re

Ra

(1 + g)

Whence, provided that the right-hand side of the last expression is zero, when all active components of the current are compensated, the dependence of the output voltage U2 of the converter on the transformed capacitance of the sensor will have the following form:

U2 -Uo

Jk.

With

Equality of the right-hand side of equation (4) 0 can be achieved by adjusting any of the transducer resistances (except for the sixth resistor) until the input phase Uo and output voltage node are out of phase. As can be seen from (5), the conversion error is 0 (yi 0), because the output voltage U2 is independent of the amplification factors of the amplifiers.

The methodological error for the prototype is described by the following expression:

} -

C „+ Cx

(1 + Cu4) Co + Cx

From a comparison of the expressions for yi m yi, it can be seen that the claimed device eliminates the error in converting the capacitance of the sensor Cx to voltage IJ2, due to the final value of the gain of the amplifier,

Thus, the inventive device provides improved accuracy.

+

JiL.

R4 R5

AND)

forming the sensor capacitance in voltage.

Compared with the prototype, the use of the proposed Converter allows you to:

-increase the accuracy of conversion of the sensor capacitance-to voltage; .

-to expand the frequency range of the converter;

- increase performance

Claims (1)

SUMMARY OF THE INVENTION A transducer of a sensor capacitance to voltage, comprising a generator, the input of which is connected to one of the terminals capacitance of the sensor, the first amplifier, the output of which is connected through the first resistor to its inverting input, and through the second resistor to the inverting input of the second amplifier, a non-inverting input which is connected to a common bus, and its output through the third resistor is connected to its inverting input and through the fourth resistor to the inverting input of the first amplifier, characterized in that, in order to improve accuracy, a sample capacitance, fifth and sixth resistors are introduced into it, the inverting input of the first amplifier is connected through the fifth resistor to the common bus, and the non-inverting input to the second output of the sensor capacitance, through the sixth resistor to the common bus and through the model capacitance to the output of the second amplifier, 4 sz8 Vo z 1g G 7 -oj s CZ TO j -ih g