SU1531005A1 - Device for measuring capacitance of sensor - Google Patents

Abstract

The invention relates to a measurement technique and can be used in devices that record changes in the parameters of dielectrics by changing their dielectric constant (capacitor capacitance). The purpose of the invention is to improve the accuracy and expand the measurement range by reducing the effect of changes in dielectric loss on the output parameter of the device. For this, a resistor is connected in parallel with the capacitive sensor whose resistance is chosen close to the capacitive resistance of the sensor. In each measurement, the resistance of the resistor and the capacitance of the sensor are equal by finding the maximum output parameter of the device. 1 il.

Description

The image relates to measurement technology and, in particular, can be used in devices that record changes in the parameters of dielectrics in terms of changes in their dielectric constant.

The purpose of the invention is to increase accuracy and expand the range of measurement of electrical capacitance by reducing the effect of changes in dielectric loss on the output parameter of the device and the ability to control the parameters of dielectrics with a high dielectric loss value.

The output parameter of the device is determined by the expression K

R,

1+ (SZSV)

)

(ABOUT

where F (J is the active component of the complex resistance

sensor with shunt resistor;

R - loss resistance circuit capacitive sensor - resistor;

C - sensor capacity;

O is the circular frequency of the device self-oscillations.

The loss resistance of the circuit capacitive sensor - shunt resistor is determined by the expression

SP

WITH

ate

 VSH - RH V RV,

(2)

where N is the loss resistance of a capacitive sensor; R is the resistance of the shunt resistor. Provided

Нц,: Н „, R ЕШ. (3)

Consequently, a change in the loss resistance of a sensor or a controlled capacitor R has almost no effect on the output parameter of the device, for which expression (1) can be written as

- RI

1 + (G) CRi

(four)

Expression (4) shows that the output parameter of the device is determined only by the capacitance of the sensor.

With R. -g :; resistance

 COOL

loss of a capacitive sensor will affect the output parameter of the device, lowering the accuracy of the device, as the condition (3) ceases to be met

one

- sensitivity

With

soy

Max

devices to change the capacity becomes insufficient to provide the necessary measurement accuracy. If the shunt resistor is made variable, then by changing it you can find the extremum of the active component of the sensor impedance with the shunt resistor.

R

and max which of the expression given the conditions of the extremum R

(four)

sh

oos

- has the meaning

a

- RIH

(five)

From the expression (5) and the extremum condition, a formula is obtained for determining the capacitance of the sensor by the extremum of the output parameter

one

WITH

2COR,

(b)

and max

The change in dielectric loss of the capacitive sensor is fully compensated by the change in the resistance of the shunt resistor, since the dielectric loss in the capacitive sensor is summed with the resistance of the shunt resistor ..

The drawing shows a block diagram of the device.

The device contains a measuring bridge 1, including resistors 2-5, a capacitor 6, a compensation element 7, a vacuum crystal oscillator 8, a capacitive sensor 9. The output of the co0 bridge

five

0

five

0

five

40

45 50

-

It is connected to the amplifier 10, two outputs of which are connected to the inputs of phase inverter 1 and the inputs of detector 12, two outputs of phase inverter 1I are connected to the inputs of the measuring bridge, two outputs of the detector are connected to the pointer 13 and to the compensation element.

The device works as follows.

When bridge 1 is unbalanced, auto-oscillations occur, their mode and amplitude are automatically kept constant by supplying the compensation element 7 with the output voltage of amplifier 10 detected by detector 12. Changes in dielectric parameters in capacitive sensor 9 associated with changes in dielectric constant and dielectric losses , leads to a change in the active and reactive components of the impedance of capacitive sensor 9.

The reactive component of the sensor impedance is compensated by a quartz resonator 8. The change in the active component of the capacitance of a capacitive sensor with a shunt resistor 5 occurs mainly as a result of a change in the capacitance of the sensor 9, since the loss capacitance of the capacitive sensor is much greater than the resistance of the shunt resistor 5. The output parameter of the device is changed for changes in the capacitance of sensor 9 causes a change in imbalance of bridge 1, which causes a change in input voltage de pointer 13 and on the compensation element 7, the total resistance of which varies in proportion to the value of the DC voltage supplied from the detector 12 in such a way as to restore the imbalance of the bridge, ensuring the stability of the amplitude of self-oscillations, and hence the stability of the amplifier 10. The scale of the pointer 13 can be made in terms of capacitance or another parameter of the dielectric depending on the capacitance of the sensor. The complete elimination of the effect of a change in the loss resistance of the capacitive sensor 9 is possible when the shunt resistor 5 is made variable. By changing the resistance of the resistor 5, maximum readings are obtained.

pointer 13, calibrated in units of the active component of the capacitance impedance of the capacitive sensor 9 with a shunt resistor 5. The change in loss resistance of the sensor 9 is compensated by the resistance of resistor 5 when adjusting the pointer J3 for maximum readings.

Due to the accuracy of measuring the parameters of dielectrics by changing their dielectric constant, the proposed device can be used to control the parameters of dielectrics with a high level of interfering side factors, for example, to control the degree of vulcanization or the degree of aging of rubber products. Full compensation of changes in dielectric loss makes it possible to control the capacitance of capacitors without evaporating them from the circuit, and also allows you to quickly and accurately control the capacitances of resistors.

Claims (1)

Claims An apparatus for measuring the electrical capacitance of a sensor, comprising a measuring bridge, the branch of which consists of resistors, Compiled by V.Semenchuk Editor A. KozorizTechred M.Didyk 31005 the bridge stroke is connected via a series-connected amplifier and a phase inverter with its own input, the amplifier output is connected to the detector input, the detector output is connected to the pointer and to the input of the compensation element included in the measuring arm of the measuring bridge in series 1Q with a vacuum quartz resonator and a capacitive sensor, and the reference arm of the measuring bridge consists of a parallel-connected variable resistor and a capacitor, one of 15 common conclusions of which are connected to a common bus, characterized in that, in order to catch measurement accuracy, a variable arm is introduced into the measuring arm of the measuring bridge 20 a resistor that is connected in parallel with a capacitive sensor, and the resistance of the variable resistor is chosen from the condition five one CO   IN WCMO.KC 1 and Cmin - circular frequencies j 0 РЫ- maximum and minimum sensor capacitance} resistance of the shunt resistor, Proofreader m.Shcharshi