SU1186938A1 - Capacitive displacement transducer - Google Patents

Abstract

CAPACITIVE TRANSFORMER CONVERTER, containing a grounded capacitive two-electrode sensor and a reference capacitor, a pulse generator and a first switch controlled by a pulse generator. characterized in that, in order to improve the accuracy of movement, the converter is equipped with a constant voltage source, a second switch, a charge integrator with a storage capacitor and an inverting adder, the first input of which is connected to the output of the integrator, the second input is connected to a constant reference source and the output through the normally closed contact of the first switch is connected to the reference capacitor, the capacitive sensor through the normally closed contact of the second switch of the bodies with It is connected to the integrator output, and the normally open contacts of the first and second switches are connected to the integrator input.

Description

one

The invention relates to a measurement technique and can be used to measure the movement of objects.

The purpose of the invention is to increase the measurement accuracy.

The drawing shows a diagram of a capacitive displacement transducer. The capacitive displacement transducer contains a capacitive sensor 1 with two electrodes 2 and 3, of which electrode 3, which is connected to an object under control (not specified), is grounded. The shielding electrode 4 is connected to the electrode 2 via a voltage follower 5. The ground capacitor 6 has one grounded electrode. The capacitive displacement transducer also contains a source of constant reference voltage 7, an inverter PI1, a first switch 9 and a second switch 10, a pulse generator 11 controlling the operation of switches 9 and 10, and a charge integrator 12 including an operational amplifier 13 and a storage capacitor 14. The non-grounded electrode of the reference capacitor 6 is connected to the normally closed contact of the switch 9, the electrode 2 of the capacitive sensor 1 is connected to the normally closed contact of the switch 10. Normally opened The contacts of the switches 9 and 10 are connected to the input of the integrator 12, the output of which is connected to the first input of the inverting adder 8. The second input of the inverting adder 8 is connected to the source 7 of a constant reference voltage.

Capacitive displacement transducer works as follows.

Moving the monitored object leads to a change in the gap between the electrodes 2 and 3 of the capacitive sensor 1. The actual value of the electrical capacitance of the capacitive sensor 1 can be represented as follows

WITH

g 8,

where S is the bottom area of the electrodes 2 and 3;

5 - the dielectric constant of the medium between the electrodes 2 and 3 {

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8 - the gap between the electrodes

2 and 3;

С -: parasitic capacitance due to the incompleteness of the shield of electrodes 2 and

3 shielding electrode 4, mounting capacity and not excluded edge effect.

О Since Sc does not depend on the value of the measured displacement, it leads to a non-linearity of the transducer's conversion function,

15 A capacitor formed by electrodes 2 and 3, when the contacts of switches 9 and 10, indicated in the drawing, are charged, is up to: the value of the output voltage of the integrator 12 charge. In this case, the reference capacitor 6 charges to the value of the output voltage of the adder 8. When the 11 capacitor pulse 1 and the reference capacitor 6 are connected to the input of the integrator 12 charge, the voltage on them becomes equal to the input voltage of the integrator 12 charge which due to

0, the high gain of the operational amplifier 13 is close to zero. In this case, the charge from sensor 1 and the reference capacitor 6 is transferred to the storage capacitor 14, changing the output voltage of the charge integrator 12 accordingly. During subsequent switchings of switches 9 and 10, the voltage at the output of the integrator 12 is charged. tends to a value at which the charges accumulated in the sensor 1 and the reference capacitor 6 are equal in absolute value and opposite in sign. The opposite of the charge signs is provided by the inverting switching on of the oleration amplifier 13. Thus, the steady state of the converter operation is described by the equation resulting from the equality of the charges on the sensor 1 and the capacitor 6

.x- Sd output output voltage

j z transducer voltage

adder 8;

GO is the capacitance of the reference capacitor 6;

31

taking into account the dependence of the output signal of the inverting adder 8 on its conversion coefficients for the first and second inputs

-V, - ". Y-K,

and

conversion factors

the value of the reference voltage

IL,

OUT c.R

.r .f .V

g -n -0 i

If the value of the coefficient K is chosen such that CpKj C, then: the effect of CD on the output characteristic of the converter will be excluded

869384

and the output voltage of the converter will be linearly related to the measured displacement.

So the signal introduction

5 feedback from the output of the converter through the inverting adder 8 allows you to eliminate the error due to parasitic capacitance, and to improve the measurement accuracy for

10 by increasing the linearity of the output characteristic. In addition, the introduction of the integrator 12 charge and the second switch, which, together with the first switch, controls the pulse generator 4–11 pulses, produces a constant voltage at the output of the inverter, which eliminates the need for rectifying the output voltage

20 similar devices to reduce accuracy.

Claims (1)

CAPACITY MOVEMENT CONVERTER containing a grounded capacitive two-electrode sensor and a reference capacitor, a pulse generator and a first switch controlled by a pulse generator, a charge integrator with a storage capacitor and an inverting adder, the first input of which is connected to the integrator output, the second input is connected to a constant reference voltage source, and the output - through the normally closed contact of the first switch is connected to the reference capacitor, the capacitive sensor through normally closed the first contact of the second switch connected to the output of the integrator, and the normally open contacts of the first and second switches are connected to the input of the integrator. SH95TT 1186938 2