JPS58155302A - Electrostatic capacity type displacement gage - Google Patents

Abstract

PURPOSE:To measure the vibration and displacement of a body highly sensitively and a highly accurately, by constituting the system so that an input voltage to a detecting end becomes large. CONSTITUTION:The AC voltage outputted from an AC oscillator 8 is amplified by a booster circuit 9 and supplied to one of electrode plates P of the detecting end. The AD signal outputted from an amplifier 2 is converted into a DC by a full wave linear detector circuit 4. The effect of a temperature drift is eliminated by a temperature compensating circuit 5. The DC signal outputted from the detector circuit 4 is smoothed by an amplfier 6, and the electric signal corresponding to a distance (d) between the electrode P and an object to be measured is outputted. The voltage, which is approximately equal to the output voltage from the amplifier 6, is outputted from a reference voltage generator 10. The output voltage from the amplifier 6 and the output voltage from the reference voltage generator 10 are compared in a differential amplifier 7 and amplified. The infinitesimal change in the distance (d) between the electrode plate P and the object to be measured is amplified by the differential amplifier 7, and the output voltage proportional to the amount of change is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitive displacement meter that measures vibration or displacement of an object to be measured by a change in capacitance between two electrodes.

Conventionally, there are eddy current type, optical type (laser), capacitance type, etc. as means for measuring minute displacements of objects without contact. Due to the measurement principle, the eddy current method is limited to conductive objects;
The measurement distance is also practically 100 square meters or less. The optical method (laser) has a high degree of freedom and high precision for length measurement, but
It is expensive and difficult to measure on irregular surfaces.

A capacitive displacement needle is a means for measuring the vibration or displacement of an object by measuring the distance between the object to be measured and the detection end using the correspondence between changes in capacitance and changes in distance. Figure 1 shows (a) and (b).
) to show its principle.

In the measurement system shown in FIG. 1(&), two electrode plates are arranged with a gap between them, and the relationship between the gap between these electrode plates and the capacitance is utilized.

When the distance between the two electrode plates is d1, the surface area of the electrode plate is S1, and the dielectric constant between the electrode plates is ε, the capacitance C between the electrode plates is given by: Therefore, d can be known from the change in C.

FIG. 1(b) shows two fixed electrode plates Pt*Pm
These fixed electrode plates Pl*Pt and one electrode plate M form two capacitances OH# Cg. If the distance between the electrode plate M and the electrode plate PIe h is d when the electrode plate - exists at the center position between the fixed electrode plates Px and Pm, then the electrode plate M is perpendicular to the plane of the electrode plate P1 or Pa. When displaced by X in the direction, two capacitances CI,
C snow is given by
can be known. As a capacitive displacement needle applying such a principle, Japanese Patent Application Laid-open Nos. 110655/1982 and 1983
There are techniques such as No.-152562 and No. F1854-41764.

However, these prior art techniques have problems with capacitive displacement needles. (1) The problem of stray capacitance between each electrode and the ground (The effect of stray capacitance between each electrode and the ground corresponding to the length of the wiring to the measuring device, and the problem of distributed capacitance in the wiring) , and (3) does not solve the problem of the presence or absence of stray capacitance to the measurement target. For example, if either electrode is grounded, the voltage converter will be unbalanced and measurement will be impossible.

The inventors have already proposed a capacitive displacement meter that solved the problems in the prior art described above in patent application No. 56-6659.
This was proposed in issue 7. This technology involves installing a pair of electrode plates facing the measurement target, surrounding each electrode plate with a grounded shield case, supplying alternating current from an AC oscillator to one of the electrode plates, and supplying alternating current to the other electrode plate. It is a system that outputs the static capacitance i between the board and the object to be measured to a voltage to a charge amplifier and an amplifier to amplify the voltage, and then outputs it to a circuit consisting of a converter that converts it into a line and outputs it as a signal. .

The present inventors further improved this capacitive displacement measurement system and invented a system that can measure the displacement, vibration, etc. of an object with high sensitivity and precision. Its features include a pair of electrode plates facing the object to be measured, a shield case surrounding each electrode plate, the shield case being grounded by a conductor, and an alternating current connected to one of the electrode plates. An AC oscillator that supplies current is provided via a booster circuit, and an amplifier consisting of a charge amplifier and a voltage amplifier that converts the capacitance between the other electrode plate and the object to be measured into voltage is provided. . The present invention will be explained in detail below.

In the measurement system proposed by the inventors in Japanese Patent Application No. 56-66597, charge amplifier 1 is used.

The relationship between the outputs is as follows! It is indicated by. Here, 1 V: output voltage at point a in FIG. 2; input voltage at point b in FIG. 2; Cf: feedback capacitance in charge amplifier 1; Cx: capacitance to be measured; Capacitance that corresponds to the distance between the tab stain electrode plate and the object to be measured.

The magnitude of the output voltage from the charge amplifier is determined by the magnitude of the capacitance Cx between the electrode plate and the object to be measured, and the input voltage V.
The size of t and the feedback capacitance Cf in the charge amplifier
Determined by Therefore, in order to increase the output of the charge amplifier in terms of the circuit for a measurement system of vibration and displacement of an object using capacitance, it is necessary to increase the input voltage Vi and to increase the feedback capacitance in the charge amplifier. It is effective to reduce Cf.

Therefore, in the present invention, the system is configured to increase the input voltage V1 to the detection terminal. FIG. 2 shows a system for measuring vibration and displacement of an object according to the present invention. In Fig. 2, the p1 electrode plate P,! :
The capacitance Cx between the objects to be measured is converted into voltage. 2
#i amplifier, which amplifies the output voltage from charge amplifier 1. 3 uses a filter to selectively extract the frequency applied to the detector 11 to improve the S/N in the measurement system. 4 is an aftereffect linear detection circuit,
The alternating current output from the filter 3 is converted into direct current.

The full-wave linear detection circuit 4 has a built-in temperature compensation circuit 5.
It functions to eliminate the temperature drift that occurs in the detection diode in the full-wave linear detection circuit 4, and the measurement system's measurement
! l! The degree decreases completely. If the measurement accuracy is ±a1,
There is no effect of 4IK temperature drift, but the measurement accuracy is ±5s.
At the level of rm@change, the influence of temperature drift becomes apparent. Although there is a method of keeping the entire circuit in an open circuit as a means to prevent the effects of temperature drift from occurring, in this invention, temperature drift can be avoided by using a circuit using a thermistor resistor and a resistor, which are inexpensive and whose circuit constants are easy to determine. The effect was removed.

Further, 6 is an amplifier which smoothes the output signal from the full-line linear detection circuit 4 and outputs an electric signal proportional to the measurement distance. 7 companies used differential amplifiers, compared the output voltage from the amplifier 6 and the output voltage from the reference voltage generator 10,
Amplify. This allows the measurement target and the detection end (electrode P) to
It is also possible to detect minute changes in distance between the two. 8 is an AC oscillator, and 9 is a booster circuit, which amplifies (external pressure) the output voltage from the AC oscillator 8 and supplies it to one of the electrode plates (P) in the detector 11. 11Fi, the detector is composed of an electrode plate (P) and a grounded shield case (S) surrounding each of the electrode plates (P). In FIG. 2, d is the distance between the electrode plate (P) and the object to be measured.

Next, the operation of the capacitive displacement needle according to the present invention constructed as described above will be explained. The voltage of the alternating current output from the alternating current oscillator 8 is amplified by the booster circuit 9 and then supplied to one of the electrode plates (P) of the detection end 11 . The capacitance Cx corresponding to the distance dK between the other stop plate (P) and the object to be measured is converted into a voltage by the charge amplifier 1, and then amplified by the amplifier 2. Since the pair of electrodes [(P) are each surrounded by a shield case C8>, the influence of stray capacitance between each electrode and the ground is eliminated. Furthermore, since the capacitance Cx is converted into a voltage by the charge amplifier and treated as a signal, the influence of stray capacitance between each electrode and the ground corresponding to the length of the wiring until it is taken out as a signal is also eliminated. The above-mentioned items eliminate the problem of the presence or absence of stray capacitance to the measurement target. The AC signal output from amplifier 2 is
The full-wave linear detection circuit 4 converts the current into direct current, and the temperature compensation circuit 5 eliminates the influence of temperature drift.

The DC signal output from the full-wave linear detection circuit 4 is smoothed by an amplifier 6, and the distance 11 between the electrode (P) and the measurement object is
It outputs nine electric signals corresponding to i1 (d). From the reference voltage generator 10, the output voltage from the amplifier 6 is t1i'.
Equal voltages are outputted by the differential amplifier 7, and the amplifier 6
The output voltage from the reference voltage generator 10 is compared and amplified.

Now, if the distance d between the electrode plate (P) and the scooped object changes slightly, the output voltage 41 of the amplifier 6 changes slightly.

This minute change is amplified by the differential amplifier 7, and nine output voltages are obtained in proportion to the amount of change. By doing so, minute changes in d on the order of μm can be detected. According to the measurement system AK according to the present invention, the capacitance of a general capacitor can be measured with high precision, and measurement of 0.019F is possible.

Since the present invention is configured and operated as described above, it is possible to measure the vibration and displacement of an object with high sensitivity and high accuracy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of a capacitive displacement needle, and FIG. 2 is a circuit diagram of a capacitive displacement meter according to the present invention. 1: Charge amplifier, 2: Amplifier, 5: Filter, 4
: full wave linear detection circuit, 5: i1 degree compensation circuit, 6: amplifier, 7: differential amplifier, 8: AC oscillator, 9: booster circuit, 10: DC reference voltage generator, 11: detector. Applicant Nippon Steel Corporation

Claims (2)

[Claims] (1) A pair of electrode plates is provided facing the measurement target, a shield case is provided surrounding each electrode plate, the shield case is grounded by a conductor, and an alternating current is supplied to one of the electrode plates. A capacitance displacement needle provided with an AC oscillator via a booster circuit, and an amplifier composed of a charge amplifier and a voltage amplifier that convert the capacitance between the other 4M board and the object to be measured into voltage. (2) A pair of electrode plates is provided facing the measurement target, and a shield case surrounding each electrode plate is provided.The shield case is grounded by a conductor, and an alternating current is supplied to one of the electrode plates. An oscillator is provided via a booster circuit, and an amplifier consisting of a charge amplifier and a voltage amplifier that converts the capacitance between the other electrode plate and the object to be measured into voltage is provided, and a full-wave linear detection circuit including a temperature compensation circuit is provided. A capacitive displacement meter is provided.