SU1337649A1 - Instrument transducer of non-electric quantities with capacitance-type sensor - Google Patents

Abstract

The invention is intended to convert changes in the capacitance of a working capacitor of a sensor into changes in a constant voltage. The purpose of the invention is to expand the functionality of the device. The converter contains stable constant voltage source 1, switches 2 and 3, rectangular voltage generator 4, amplifier 7 and phase-sensitive detector 8. Introduction of operational amplifiers 9 and 10 and the formation of new functional connections ensure the operation of the converter with various types of capacitive sensors and the ability to adjust the slope and zero offset of the transfer characteristic while maintaining its linearity and stability. 1 il. J3 / J rcfbUx so oo O) i4; o

Description

The invention relates to a measurement technique, can be used to measure various non-electric quantities (displacement, angle, rotation, substance level, etc.) and is intended to convert changes in the capacitance of an operational capacitor of a sensor into constant voltage variations .IQ

The aim of the invention is to enhance the functionality of the converter by providing its operation with various types of capacitive sensors, as well as by providing the ability to adjust the slope and zero the transfer characteristic while maintaining its linearity and stability.

The drawing shows the functional diagram of the Converter.

The device contains a source of stable DC voltage, switches 2 and 3, a generator 4 of a rectangular voltage, working 5 and 6 capacitors, yci-7, phase-sensitive detector 8, operational amplifiers 9 and 10, resistors 11-17, output terminals 18 devices. With

The device works as follows.

The potential electrodes of the working capacitors 5 and 6 of the sensor are supplied by antiphase rectangular voltages generated by switch 2 from the output voltage of the first operational amplifier 9 and switch 3 from the output voltage of the operational amplifier 10. Switches 2 and 3 are controlled by a rectangular voltage generator 4 . In case of disequilibrium of the circuit (when the ratio of capacitances C15 and C6 of the capacitors 5 and 6 of the sensor is not equal to the inverse ratio of the voltages applied to them) on the connected electrodes of the operating capacitors 5 and 6

20 a differential signal acts, which is amplified by amplifier 7. The phase of the square signal at the output of amplifier 7 depends on the equilibrium sign of the circuit. This rectangular voltage is applied to the input of the phase-sensitive detector 8, which forms a constant voltage at its output, which is supplied for the weekend

The terminals 18 of the device and through the resistors resistors 11 and 12 are connected the odors 15 and 16 to the inverting inputs from the terminals respectively to the output amplifiers 9 and 10, respectively, of the operational amplifiers 9 and 10, respectively. The same inputs through the second terminals - to their inverting resistors 13 and 14 are supplied to the stabilized inputs to which through a resistor of a constant voltage of 13 and 14 is connected the source 1 of the constant source 1. To the inverting input the second voltage, and through the resistors 15 and 16 - the output of the device, the output of the opalI of the amplifier 9 is connected through the resistor 17 to the inverting input of the operational amplifier 10, and the non-inverting inputs of the operating

The output voltage of the first operational amplifier 9 is also supplied through the resistor 17. Thus, a change of 40 in the output voltage of the phase-sensitive detector 8 causes a change in

the amplifiers are connected to the common bus, the first information inputs of the switches 2 and 3 are connected respectively to the outputs of the operational amplifiers 5 bb voltages on the potential

9 and 10, and their second inputs to the common electrodes of capacitors 5 and 6 of the sensor, the outputs of switches 2 and 3 are connected to potential electrodes of working capacitors 5 and 6, the second — current electrodes of which are connected and connected to the input of the expander 7, the output of which is connected to the input of the phase-sensitive detector B, the output of the square voltage generator 4 is connected to the control inputs of the switches 2 and 3 and the reference input of the phase-sensitive detector 8, the output of which is connected to the output terminals 18 of the device.

The device works as follows.

The potential electrodes of the working capacitors 5 and 6 of the sensor are supplied by antiphase rectangular voltages generated by switch 2 from the output voltage of the first operational amplifier 9 and switch 3 from the output voltage of the operational amplifier 10. Switches 2 and 3 are controlled by a rectangular voltage generator 4 . In case of disequilibrium of the circuit (when the ratio of capacitors C5 and C6 of the working capacitors 5 and 6 of the sensor is not equal to the inverse ratio of the voltages applied to them) at the connected electrodes of the working capacitors 5 and 6

A difference signal acts on the sensor, which is amplified by amplifier 7. The phase of the square signal at the output of amplifier 7 depends on the equilibrium sign of the circuit. This rectangular voltage is applied to the input of the phase-sensitive detector 8, which forms a constant voltage at its output, which is supplied for the weekend

the terminals 18 of the device and through the resistors 15 and 16 to the inverting inputs of the operational amplifiers 9 and 10, respectively. The same inputs through resistors 13 and 14 are supplied with a stabilized DC voltage of source 1. At the inverting input of the secondary

The output voltage of the first operational amplifier 9 is also supplied through the resistor 17. Thus, a change in the output voltage of the phase-sensitive detector 8 causes a change in

output voltages Ug and V, operational amplifiers 9 and 10, respectively, which leads to a change in the ratio

k and to a decrease in the voltage unbalance. This process continues until the circuit is balanced, i.e. the disequilibrium voltage will not become zero. Thereafter, the constant voltage at the output of the phase-sensitive detector 8 remains unchanged until the capacitances of the operating capacitors 5 and 6 of the sensor change again.

In the balanced state of the circuit with sufficiently large gains of the operational amplifiers 9

and 10, as well as the amplifier of equations describing properties, has the form: Ug-Cj + U ,, - C, 0,

and 11 5g T 5i.

3 ° R „. vih R.

and - 1t (-

  .R

 H

hb "

R ,,

(one)

the output voltage of the device (acting at the output 18);

stabilized constant voltage source 1; resistance resistors

11-17, respectively. system (1) gives the following transformation device

R ,.

rRl2RI- Rl2

lm p j-f 12 / -I

p 5 p P g 91

JSHI - pDDP

Cc ,, 4. g 2 g

R G R R V I. k, k, fc

By choosing different ratios between the values of resistance, it is possible to obtain various transfer characteristics of the device. Consider some typical examples.

The sensor is differential, and in the middle position of the moving electrode (at) the output voltage must be zero. In this case, the transfer function must be

Cf-ct

proportional to the value ---, with С j + Cj

than R, R ,,,, R ,, j, and the resistor 14 is excluded from the circuit ((R), Then from (2) we get

- iTlEfjEt

By changing the ratio R, j / R, 3, one can obtain the necessary slope of the transformation without changing the position of the zero reference.

The sensor is also differential, but a zero shift of the reference is required, and, as in the previous case, R ,, ,, ,,, P ,, however, resistor 14 is left in the circuit.

Substitute these relations in the formula (2)

th

n

you are -Uo

1 g + c5i Bi) g

p At Vp TK 4 K.1 1X14 K, j

, + c,

 and convert this expression to the following form:

TI - tt Ch h R) 5 1,. . V

Ua ..- Ue (R-- 2k:; - s; TS2k7

As can be seen from the obtained formula, by changing the resistance R, one can choose the position of the zero reference (at the same time, in order to maintain the same steepness, R must also be adjusted at the same time, so that the value 1513

- - - remained constant), and iz p m

The magnitude of R is to obtain the necessary steepness of the transfer characteristic.

The sensor is not differential with variable area electrodes. In this case, to obtain a linear reference, the output voltage must be proportional to the ratio C5 / C6, if the capacitance C5 is variable, and C6 is constant (exemplary). Eliminate from the circuit resistors 15, 17, and resistors 11 and 12 will make the same, in

30, according to which we shall substitute the following values into formula (2): R R,

R.r.

then

and ...- and „. (1-2- + 1).

 tblf

Ri3-c,

R,

(five)

In this case, by changing the resistance R, j, the steepness can be adjusted, and by changing the resistance R ", the zero position can be adjusted.

The sensor is not differential, with a variable gap between the flat electrodes. In this case, to obtain a linear dependence of the output signal on the displacement, it is necessary that

the voltage was inversely proportional to the capacity of the working capacitor. The device is suitable for operation and in this case it is only necessary to turn on the sensor so that its variable

the working capacitor was in place of capacitor 6, and a constant (exemplary) one was in place of capacitor 5. The choice of resistors and coupling for Uj, while being the same as in the previous case.

Claims (1)

Invention Formula Non-electric measuring transducer with capacitive sensor, containing two switches, the second information inputs of which are connected to the common bus, and the outputs - to the potentials of the two working capacitors of the sensor, the current electrodes of which are connected and connected through an amplifier to the input of the phase-sensitive detector, the output of which is rectangular voltage, the output of which is connected to the control inputs of the switches and the reference input of the phase-sensitive detector, and a source of stable constant voltage, is distinguished by iys in that, in order to expand the functionality of the transducer by providing it with different types emkoRedaktor N.Gorvat Compiled by N.Mikhalev Tehred M. Khodanich Proofreader L. Bezkid Order 4117/35 Circulation 676 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 ... K.SH..I. .- ". HVH". Production and printing company, Uzhgorod, st. Project, 4 five It is equipped with two operational amplifiers, the outputs of which are connected directly to the first information inputs of the switch and, through resistors, to their inverting inputs, which also A source of a stable constant voltage and an output of a phase-sensitive detector are connected through appropriate resistors; the output of the first operational amplifier The resistor is connected to the inverting input of the second opamp, and their non-inverting inputs are connected to the common bus.