JPH06241706A - Capacitance type displacement gauge - Google Patents

Abstract

PURPOSE:To eliminate the floating capacity and distributing capacity around an electrode, and precisely measure an electrostatic capacity by providing a slide shaft capable of sliding in a cylindrical outer cylinder, and the electrode on the outer circumferential surface thereof. CONSTITUTION:A metal slide shaft 4 is mounted in an outer cylinder 27 in such a manner as to be capable of sliding, and the central part is continued to a major diameter part 4a. In adjacent positions to the outer circumference of the major diameter part 4a, cylindrical electrodes 2A, 2B are arranged. Cylindrical guard electrodes 3A, 3B are inserted between the electrodes 2A, 2B and the outer cylinder 27, whereby a precision reduction by the distributing capacity between the electrodes 2A, 2B and the outer cylinder 27 is eliminated. Insulating rings 28, 29, 30 are inserted among the electrodes 2A, 2B, the guard electrodes 3A, 3B, and the outer cylinder 27, respectively. The electrodes 2A, 2B and the guard electrodes 3A, 3B are connected to the internal conductors 5A, 5B and external conductors 6A, 6B of two coaxial cables, respectively, and delivered to an external control part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type displacement meter which detects changes in capacitance and equivalently measures changes in physical quantity.

[0002]

2. Description of the Related Art Capacitance type displacement gauges are used for measurement of permittivity, displacement and thickness, but in principle they have the following problems.

1) The electrode surface (side surface, back surface) other than the detection surface and the cable between the electrode and the control unit are also a part of the electrode, and these are affected by the stray capacitance, resulting in a decrease in accuracy.

2) Floating capacitance can be cut off by surrounding the electrode with a grounded case and by using a coaxial cable between the electrode and the control unit and grounding the outer conductor of the coaxial cable. A large amount of distributed capacitance is generated between the outer conductor and the inner conductor of the cable, which lowers the detection accuracy.

FIG. 12 shows an example of a conventional measuring method.

As described above, in the related art, no electrical countermeasures against the above-mentioned problems have been taken. Therefore, the precision is greatly reduced due to the stray capacitance or the distributed capacitance generated in the electrode and the cable between the electrode and the control unit. In order to prevent the decrease, the electrode and the control unit are integrated.

Originally, the capacitance type electrode has only to have a conductive surface and has a characteristic that a required shape such as a cylindrical shape or a roller shape can be easily obtained. Therefore, the conventional method is inevitably integrated. Because of this, this feature was not utilized.

When the capacitance is measured and the permittivity or displacement is equivalently measured, a resistance may be added in series or in parallel to the detection capacitance, but the conventional method is to use this series or parallel. The capacitance to be detected by the resistance could not be measured correctly.

For example, FIG. 13A shows an example of measuring the distance between electrodes and a material having a low conductivity such as a semiconductor. In this case, as shown in FIG. 13B, the detection capacitance C ₁ is connected in series. Since the resistance r of the semiconductor was added to, the distance d could not be measured correctly.

FIG. 14A shows an example of measurement of the dielectric constant,
In this case, as shown in FIG. 14B, the resistance r of the dielectric substance was added in parallel with the detection capacitance C ₁ , and the accurate dielectric constant could not be measured.

Further, although a differential transformer type has been conventionally used for this type of displacement gauge, it is expensive because it requires a coil to be wound.

[0012]

The problem to be solved by the present invention is to eliminate the stray capacitance and distributed capacitance around the electrodes, and to make it possible to separate the detection unit and the control unit without lowering the detection accuracy. An object of the present invention is to provide a capacitance displacement meter that can accurately measure the capacitance without being affected by the resistance applied in series or in parallel to the detection capacitance.

[0013]

In order to solve this problem, a capacitance type displacement gauge according to the present invention comprises a metal slide shaft slidably mounted on a cylindrical outer cylinder, and the outer cylinder. An electrode disposed in the vicinity of the outer circumference of the slide shaft, and a capacitance-voltage for converting the magnitude of the capacitance between the slide shaft and the electrode into the magnitude of the amplitude of the AC voltage. It is configured to include a conversion circuit and output means for converting the output of the capacitance-voltage conversion circuit into the displacement of the slide shaft and outputting the displacement.

[0014]

When the slide shaft is moved in the longitudinal direction with respect to the outer cylinder, the magnitude of the electrostatic capacitance between the slide shaft and the electrode changes according to the displacement. Therefore, by converting the change in the capacitance into a voltage, an output according to the magnitude of the displacement can be obtained.

Further, the guard poles surrounding the electrodes and the outer conductor of the coaxial cable are driven by the voltage follower amplifier to almost the same potential as that of the inner conductor of the electrode and the coaxial cable. The distributed capacitance is made minute and the stray capacitance is cut off. Moreover, the detection direction can be limited by surrounding a part of the electrode with the guard electrode.

The sampling circuit outputs the difference between the voltage follower amplifiers as a voltage proportional to the detected electrostatic capacity. The output is between the electrode and the guard pole and between the inner conductor and the outer conductor of the coaxial cable. A component proportional to the distributed capacitance and a component proportional to the resistance added in series / parallel to the detection capacitance are included as the in-phase component of the mutual product of the voltage follower amplifier outputs.

Since the component proportional to the detected capacitance is the 90 ° delayed phase of the product of the voltage follower amplifiers, the sampling circuit samples by the 90 ° delayed phase of the product of the voltage follower amplifiers.
Only the component proportional to the detected capacitance is output. If there is only one electrode, insert a capacitor equal to the sum of the distributed capacitance between the electrode and the guard pole and the inner and outer conductors of the coaxial cable between the inputs of the voltage follower amplifier to which the electrode is not connected. As a result, the in-phase component due to the distributed capacitance of the mutual products can be reduced.

[0018]

EXAMPLES The present invention will be specifically described below based on examples. [First Embodiment] FIG. 1 shows a first embodiment of the present invention, showing a case of a differential type having two electrodes. A metal slide shaft 4 is slidably mounted in the outer cylinder 27, and the central portion or neutral position of the slide shaft 4 is a large diameter portion 4a. Cylindrical electrodes 2A and 2B are arranged at positions close to the outer circumference of the large diameter portion 4a. By inserting the cylindrical guard electrodes 3A and 3B between the cylindrical electrodes 2A and 2B and the outer cylinder 27, the electrode 2
The accuracy deterioration due to the distributed capacitance between A and 2B and the outer cylinder 27 is eliminated, and the capacitance type can be applied to this type of length measuring device. Electrodes 2A, 2B, guard electrodes 3A, 3B and outer cylinder 27
Insulating rings 28, 29, 30 are inserted between them, and these insulating rings have capacitances between the electrodes 2A, 2B and the guard electrodes 3A, 3B, and between the guard electrodes 3A, 3B and the outer cylinder 27. Since the decrease in accuracy due to the above is small, there is no problem even if the material has a relatively large variation in the dielectric constant.

The cylindrical electrodes 2A and 2B and the guard electrode 3A,
3B are inner conductors 5A and 5 of two coaxial cables, respectively.
B and the external conductors 6A and 6B are connected to the external control unit. In the present embodiment of FIG. 1, the control unit is separated from the detection unit 1, so that it can be used even at high temperatures.

FIG. 2 is a circuit diagram showing the detection unit 1, the capacitance-voltage conversion circuit 7 and the coaxial cable in the capacitance type displacement meter of the present invention.

FIG. 3 shows the capacitance of the detector 1 according to the present invention.
Equivalent circuit up to voltage conversion circuit 7 and sampling circuit 1
6 shows a block diagram of 6. In FIG. 3, C ₁ and C ₂ are the detected capacitances between the electrodes 2A and 2B in FIG. 2 and the slide shaft 4 connected to the common potential COM, and C ₃ and
C ₄ is a distribution between the guard electrodes 3A and 3B and the common potential COM, between the outer conductors 6A and 6B of the coaxial cable and the common potential COM, and between the cable between the voltage follower amplifiers Q ₁ and Q ₂ and the sampling circuit 16 and the common potential COM. The sum of the capacitances, C ₅ and C _6, are the electrodes 2A. 2B and guard pole 3A. 3B
Inner conductors 5A and 5B and outer conductor 6 of the inter- and coaxial cables
It is the sum of the distributed capacities between A and 6B.

The effect of the capacitance generated around the detector and the coaxial cable on the accuracy will be described in detail below.

[Capacitance-Voltage Conversion Circuit 7] The relationship between the loop gain A _f of the voltage follower amplifiers Q ₁ and Q ₂ and the gain error ε at the oscillation frequency of the sine wave oscillator OSC can be approximated by the equation (1). ε = 1 / (jA _f ) ... (1)

[0024] Therefore, the output voltage e ₁ of the voltage follower amplifier Q ₁ is a (2). e ₁ = {(1-εR ₀ ωC ₅ ) e _i } / [1-εR ₀ ω (C ₃ + C ₅ ) -εR ω (C ₁ + C ₅ ) + jRωC ₁ {1-εR ₀ ω (C ₃ + C ₃ · C ₅ / C ₁ + C ₅ )} + jε] ・ ・ ・ (2)

From this equation, the effect of C ₅ on e ₁ is
Has a substantially ε doubled compared to that of C _1, effects on e ₁ of C ₃ It can be seen that even smaller almost .epsilon.R ₀ / R times the C ₁ (generally R»R _0).

[0026] If the opposite view, can be considered as substantially the capacitance of C ₅ is substantially the capacitance of C ₅ × epsilon, C ₃ became C ₃ × εR ₀ / R. This is the effect of driving the guard pole and the outer conductor of the coaxial cable with the voltage follower amplifier.

[Sampling Circuit 16] The sampling circuit 16 outputs the difference between the voltage follower amplifiers as the displacement amount. The output is between the electrode and the guard pole and between the inner conductor and the outer conductor of the coaxial cable. A component proportional to the sum of the distributed capacitance of is included as the in-phase component of the mutual product of the voltage follower amplifier outputs.

The component proportional to the displacement is the 90 ° delayed phase of the product of the voltage follower amplifiers, so 90
By sampling with a phase delay, only the component proportional to the displacement can be output.

The sampling circuit 16 further reduces the influence on the accuracy of C ₅ and C ₆ which have the greatest influence in the equation (2), and the equation (2) eliminates the term having a small influence. If it does, it will become a formula (3). e ₁ = e _i / {1-εRω (C ₁ + C ₅ ) + jωC ₁ } (3)

The same output voltage e ₂ of the voltage follower amplifier Q ₂ is (4). e ₂ = e _i / {1-εRω (C ₂ + C ₆ ) + jωC ₂ } (4)

The output e ₃ = e ₁ -e ₂ of the subtractor 10 is
From equations (3) and (4), equation (5) is obtained. e ₃ = {εRω (C ₁ -C ₂ + C ₅ -C ₆ ) -jRω (C ₁ -C ₂ ) e ₁ } / [{1-εRω (C ₁ + C ₅ ) + jRωC ₁ } {1- εRω (C ₂ + C ₆ ) + jRωC ₂ }] ・ ・ (5)

Expression (5) is a phase reference of e _i , and when this is used as a phase reference of e ₁ × e ₂ , expression (6) is obtained and the denominator is only the in-phase component. e ₃ '= {εRω (C ₅ -C ₆ ) -jRω (C ₁ -C ₂ ) e ₁ } / ([{1-εRωC ₅ } ² + {RωC ₁ } ² ] ^1/2 × [{1- εRωC ₆ } ² + {RωC ₂ } ² ] ^1/2 ) (6)

The sampling circuit 16 is a phase reference of e ₁ × e ₂ and samples only the 90 ° phase delay, and eliminates the first term of the equation (6) which changes depending on C ₅ and C _6. Then, the second of the formula (5) proportional to the detected capacitance
It is intended to retrieve only terms.

In FIG. 2, the output e ₄ of the adder 12 is given by equation (7). e ₄ = {2-εRω (C ₅ + C ₆ ) + jRω (C ₁ + C ₂ )} e _i / ([1-εRωC ₅ + jRωC ₁ ] [1-εRωC ₆ + jRωC ₂ ]) ・ ・ ・(7)

The delay circuit 13 has a delay angle Q of (8).
Select the resistor and capacitor so that Q = tan ^-1 [-Rω (C ₁ + C ₂ ) / {2-εRω (C ₅ + C ₆ )}] (8)

In the case of the differential type, C ₁ + C ₂ is generally constant, and it is not necessary to change Q depending on the detected electrostatic capacity.

From the equations (7) and (8), the output e ₅ of the delay circuit 13 becomes the equation (9), which is in phase with e ₁ × e ₂ . e ₅ = e ₄ × [2-εRω (C ₅ + C ₆ ) -jRω (C ₁ + C ₂ )] = [{2-εRω (C ₅ + C ₆ )} ² + {Rω (C ₁ + C ₂ )} ² ] e _i / [{1-εRωC ₅ + jRωC ₁ } {1-εRωC ₆ + jRωC ₂ }] = e ₁ × e ₂ [{2-εRω (C ₅ + C ₆ )} ² + { Rω (C ₁ + C ₂ )} ² ] / e _i・ ・ ・ ・ (9)

The comparator 14 makes e ₅ a square wave.
The signal of the output e ₆ is inverted at the point where the phase of e ₅ is shifted by 90 °.

The output e ₃ of the subtractor 10 becomes the analog input of the sample and hold circuit, and the output e _{6 of the} comparator 14
Becomes a hold signal, the sample and hold circuit samples e ₃ at the phase reference of e ₁ × e ₂ and at a point where the phase is delayed by 90 °.
Since the in-phase component of the equation (6) disappears and the crest value for the 90 ° phase delay is obtained, the equation (10) is obtained if e _i is an effective value. E = √2Rω (C ₁ -C ₂ ) e _i / ([{1-εRωC ₅ } ² + {RωC ₁ } ² ] ^1/2 × [{1-εRωC ₆ } ² + {RωC ₂ } ² ] ^{1 / 2} ) ・ ・ ・ (10)

From the above, it can be seen that the influence of the capacitances C ₅ and C ₆ generated around the electrodes and the coaxial cable on the output E is very small.

The sample signal using the output e ₇ that a square wave by the comparator 15 outputs e _i sine wave oscillator (OSC).

The voltage waveform of each part is shown in FIG. Here e _3r is e ₁ × e _2-phase component of e _3, e _3x is 90 ° phase delay component.

[Second Embodiment] FIG. 5 shows a second embodiment of the present invention. The first embodiment is a differential type having two electrodes, whereas the second embodiment is an electrode 1. I am individual. A metal slide shaft 4 is slidably mounted in the outer cylinder 27, and a cylindrical electrode 2 is arranged on the outer circumference of the slide shaft 4. By inserting the cylindrical guard electrode 3 between the cylindrical electrode 2 and the outer cylinder 27, the accuracy deterioration due to the distributed capacitance between the electrode 2 and the outer cylinder 27 is eliminated,
Capacitance type can be applied to this type of length measuring device.
An insulating ring 2 is provided between the electrode 2, the guard electrode 3 and the outer cylinder 27.
Although 8 and 30 are inserted, these insulating rings are
Since the decrease in accuracy due to the electrostatic capacitance between the electrode 2 and the guard electrode 3 and between the guard electrode 3 and the outer cylinder 27 is very small, there is no problem even if the material has a relatively large variation in dielectric constant.

The cylindrical electrode 2 and the guard electrode 3 are connected to the inner conductor 5 and the outer conductor 6 of the coaxial cable and led to an external control section. In this embodiment shown in FIG. 5, the control unit is the detection unit 1.
Since it is separated from, it can be used even at high temperatures.

FIG. 6 shows the detection unit 1, the capacitance-voltage conversion circuit 7 and the coaxial cable in the capacitance type displacement meter of the present invention. As shown in the figure, the guard electrode 3 and the outer conductor 6 of the coaxial cable are connected to the voltage follower amplifiers Q ₁ and Q ₂
Are driven to the same potential as the electrode 2 and the inner conductor 5 of the coaxial cable.

FIG. 7 shows the capacitance of the detector 1 according to the present invention.
Equivalent circuit up to voltage conversion circuit 7 and sampling circuit 1
6 shows a block diagram of 6.

In the figure, C ₁ and C ₂ are detection capacitances between the electrode 2 and the counter electrode 4 connected to the common potential COM in FIG. 6, and C ₃ and C ₄ are the guard electrode 3 and the common potential. C
Common potential COM between the OM and the outer conductor 6 of the coaxial cable
Between the voltage follower amplifiers Q ₁ and Q ₂ and the sampling circuit 16 and the sum of the distributed capacitance between the common potential COM, C ₅ and C ₆ are between the electrode 2 and the guard pole 3, and between the inner conductor 5 and the outside of the coaxial cable. It is the sum of the distributed capacitances between the conductors 6.

In FIG. 7, C ₁ , C ₃ and C ₅ have the same contents as in FIG. C _2b and C _6b are fixed capacitors, C _3b is a voltage follower amplifier Q ₂ to a sampling circuit 1
6 is a distributed capacitance between the cable between 6 and the common potential COM.
Further, R is a fixed resistance, R ₀ is an output resistance of the voltage follower amplifiers Q ₁ and Q ₂ , and e _i is an output voltage of the sine wave oscillator OSC.

Differences between the second embodiment and the first embodiment will be described below. In the case of this embodiment having one electrode, FIG.
As shown in, the capacitors C _2b and C _6b that are equal to the sum of the distributed capacitance between the electrode and the guard electrode and the inner and outer conductors of the coaxial cable are connected between the inputs of the voltage follower amplifier Q ₂ where the electrodes are not connected. By inserting, the in-phase component of mutual products can be reduced.

In FIG. 7, the output voltage e _2b of the voltage follower amplifier Q ₂ is given by equation (11), and the output e _3b ′ of the subtracter 10 based on the phase of e ₁ × e _2b is given by equation (12). e _2b = e _i / (1-εRωC _6b + jRωC _2b ) ・ ・ ・ ・ ・ ・ (11) e _3b '= {εRω (C ₁ -C _2b + C ₅ -C _6b ) -jRω (C ₁ -C _2b )} e _i / [√ [1-εRω (C ₁ + C ₅ )] ² + (RωC ₁ ) ² × √ [1-εRω (C _2b + C _6b )] ² + (RωC _2b ) ² ] ・... (12)

C _6b is a capacitor having the same capacity as C ₅ (C _6b =
If C ₅ ), the in-phase component of the equation (12) is eliminated and the accuracy is improved.

When the number of electrodes is one, the adder 12 of FIG. 3 of the first embodiment is not provided and e ₁ is the input of the delay circuit 13. When the delay angle θ _b of the delay circuit 13 is represented by the equation (13), the output e _5b of the delay circuit 13 is represented by the equation (14), and e ₁ ×
Be in phase with e ₂ . θ _b = tan ^-1 [(-RωC _2b ) / {1-εRω (C _2b + C _6b )}] ... (13) e _5b = e ₁ [1-εRω (C _2b + C _6b )- jRωC _2b ] = e ₁ · {[1-εRω (C _2b + C _6b )] ² + (RωC _2b ) ² } / [1-εRω (C _2b + C _6b ) + jRωC _2b ] = e ₁ e _2b { _{[1-εRω (C 2b +} C 6b)] 2 + (RωC 2b) 2} / e i ···· (14)

Similarly to the differential type of the first embodiment, if the comparator 14 converts the square wave of e _5b and the output e _6b of the square wave is used as the hold signal, the DC output E _b of the sample and hold circuit becomes (1
It becomes the formula 5). E _b = √2 Rω (C ₁ -C _2b ) e _i / [√ {[1-εRω (C ₁ + C ₅ )] ² + (RωC ₁ ) ² } × √ {[1-εRω (C _2b + C _6b )] ² + (RωC _2b ) ² }] ··· (15)

Similar to the equation (10), the equation (15) has a small influence on the output E _b of the capacitance C ₅ generated around the electrodes and the coaxial cable.

[Third Embodiment] A case where series resistance is applied is, for example, a case where a distance between a semiconductor and an electrode is measured.
The differential type with two electrodes is not used.

FIG. 8 shows a block diagram of an equivalent circuit from the detecting section to the electrostatic capacitance-voltage conversion circuit in the case of one electrode and the sampling circuit. In the figure, c ₃ and c ₄ are omitted because they have little influence on accuracy as described above. It is a resistance that r is added in series. In addition, fixed capacitor c _6b
I have removed it because it is better not to. The outputs e _1c and e _2c of the voltage follower amplifiers Q ₁ and Q ₂ are (1
Equations 6) and (17) are obtained. e _1c = [(1 + jrωC ₁ ) / {1-εRωC ₅ + j (R + r) ωC ₁ }] e _i ... (16) e _2c = [1 / (1 + jRωC _2b )] e _i (17) Therefore, the output e _3c = e _1c -e _2c of the subtractor 10 is given by the expression (18). e _3c = [{εRωC ₅ -rωC ₁ · RωC _2b -jRω (C ₁ -C _2b )} / {[1-εRωC ₅ + j (R + r) ωC ₁ ] (1 + jRωC _2b )}] e _i ... (18)

When the delay angle θ _c of the delay circuit 13 is expressed by equation (19), the DC output E _c becomes equation (20) by eliminating the in-phase component of the numerator of equation (18). ^{_{θ c = tan -1 (-RωC 2b}} ) ···· (19) E c = {√2Rω (C 1 -C 2b) e i / [√ {(1-εRωC 5) 2 + [(R + r ) ωC ₁ ] ² } × √ {1+ (RωC _2b ) ² }] ··· (20)

From the equation (20), it is understood that the influence of the series resistance r on the output E _c is very small.

[Fourth Embodiment] When a parallel resistance is added,
As in the case of the third embodiment, the one-electrode type is used, for example, in the case of measuring the dielectric constant or measuring the dielectric constant and equivalently measuring the water content.

FIG. 9 shows a block diagram of an equivalent circuit from the detection unit to the electrostatic capacitance-voltage conversion circuit in the case of one electrode and the sampling circuit.

In the figure, r is a resistance added in parallel. C _3, C ₄ are omitted as in the second embodiment. The outputs e _1d and e _2d of the voltage follower amplifiers Q ₁ and Q ₂ are expressed by equations (21) and (22), respectively. e _1d = e _i / (1-εRωC ₅ + R / r + jRωC ₁ ) ・ ・ ・ ・ (21) e _2d = e _i / (1-εRωC _6b + jRωC _2b ) ・ ・ ・ ・ (22)

Therefore, the output of the subtractor 10 e _3d = e _1d -e _2d
Becomes equation (23). e _3d = {εRω (C ₅ -C _6b ) -R / r-jRω (C ₁ -C _2b )} e _i / {(1-εRωC ₅ + R / r + jRωC ₁ ) (1-εRωC _6b + jRωC _2b )} (23) _Let the delay angle θ _d of the delay circuit 13 be the expression (24). θ _d = tan ^-1 {-RωC _2b / (1-εRωC _6b )} (24)

Therefore, the DC output E _d becomes the equation (25) when the in-phase component of the numerator of the equation (23) disappears. E _d = {√2Rω (C ₁ -C _2b ) / [√ {(1-εRωC ₅ + R / r) ² + (RωC ₁ ] ² } × √ {(1-εRωC _6b ) ² + (RωC _2b ) ² }] ・ ・ ・ ・ (25)

From the equation (25), in the range of R << r,
The influence of the parallel resistance r on the output E _d is small.

[Fifth Embodiment] FIG. 10 shows an example in which the capacitance-voltage conversion circuit 7 is built in the outer cylinder 27 in the second embodiment, and there is no reduction in accuracy due to the coaxial cable. Although it is a feature, the detector 1 cannot be used in a high temperature atmosphere above the operable temperature of the circuit.
Suitable for use at room temperature.

[Sixth Embodiment] FIG. 11 shows an example of a detecting portion applied to the thickness detection of an insulating measured object 34. A roller that can be moved up and down depending on the thickness is used as the electrode 32, and an auxiliary device is not required, and the structure is simple. Guard pole 3
3 cuts off the stray capacitance and detects only the fixed roller 40. Further, this method has a large detection capacitance, can detect a minute change in thickness with high accuracy, and does not cause an error due to a change in resistance of an object to be measured.

[0067]

As described above, the present invention has the following effects. Since the coil system is not used as the displacement meter and the displacement is converted into the capacitance, it is possible to manufacture one having a long measuring stroke, the accuracy and resolution do not change, and the cost can be reduced.

The electrode part and the control part can be separated with a minute precision or less, and the guard electrode can eliminate the stray capacitance and the distributed capacitance around the electrode and give the electrode a detection directionality.

The electrode portion has a simple structure including only electrodes and guard electrodes, and can be formed into any shape such as a cylindrical shape or a roller shape. Further, there is no decrease in accuracy due to the resistance of the semiconductor and the dielectric that are added in series and parallel to the detection capacitance.

From the above, application to a wider range of applications becomes possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a detection unit showing a first embodiment.

FIG. 2 is a circuit diagram showing a differential type embodiment with two electrode units from a detection unit to a capacitance-voltage conversion circuit.

FIG. 3 is a block diagram of a differential equivalent circuit from a detection unit to a capacitance-voltage conversion circuit and a sampling circuit of the first embodiment.

FIG. 4 is a waveform diagram showing voltage waveforms of respective parts in FIG.

FIG. 5 is a cross-sectional view of a detection unit showing a second embodiment.

FIG. 6 is a circuit diagram showing an embodiment in which there is one electrode unit from the detection unit to the capacitance-voltage conversion circuit.

FIG. 7 is a block diagram of an equivalent circuit and a sampling circuit in the case where there is one electrode unit from the detection unit to the electrostatic capacitance-voltage conversion circuit of the second embodiment.

FIG. 8 is a block diagram of an equivalent circuit from a detection unit to a capacitance-voltage conversion circuit and a sampling circuit in the third embodiment.

FIG. 9 is a block diagram of an equivalent circuit showing a fourth embodiment.

FIG. 10 is a sectional view of a detection unit showing a fifth embodiment.

FIG. 11 is a sectional view of a detection unit showing a sixth embodiment.

FIG. 12 is a circuit diagram showing a known capacitance type displacement meter.

FIG. 13 is a circuit diagram showing a measurement example according to the present invention and an equivalent circuit thereof.

FIG. 14 is a circuit diagram showing another measurement example according to the present invention and its equivalent circuit.

[Explanation of symbols]

1 detector, 2, 2A, 2B electrodes, 3, 3A, 3B
Guard electrode, 4 slide shaft, 5, 5A, 5B
Inner conductor of coaxial cable, 6, 6A, 6B Outer conductor of coaxial cable, 7 Capacitance-voltage conversion circuit, 10 Subtractor, 11 Sample and hold circuit, 12 Adder,
13 delay circuits, 14, 15 comparators, 16 sampling circuits, 24 slide shafts, 27 outer cylinders, 2
8, 29, 30 Insulation ring, 34 Insulation DUT,
37 columns, 38, 39 insulating spacers, 40 fixed rollers

Claims (8)

[Claims] 1. A metal slide shaft (4) slidably mounted on a cylindrical outer cylinder (27), and a metal slide shaft (27) disposed in the outer cylinder (27) close to the outer circumference of the slide shaft (4). Capacitance-voltage conversion for converting the magnitude of the capacitance between the electrode (2) arranged as a unit and the slide shaft (4) and the electrode (2) into the magnitude of the amplitude of the AC voltage. A capacitance type displacement comprising a circuit (7) and an output means for converting the output of the capacitance-voltage conversion circuit (7) into the displacement of the slide shaft (4) and outputting the displacement. Total. 2. A capacitance-voltage conversion circuit (7) comprises a plurality of capacitances and resistors (R) formed by electrodes (2) or fixed capacitors (C _6b ) and resistors (R). A delay circuit and a plurality of voltage follower amplifiers (Q ₁ ), which drive the outer conductor (6) of the coaxial cable and the conductor (3) surrounding a part of the electrode (2) by using the output of the delay circuit as an input. _{2. The} capacitance type displacement meter according to claim 1, comprising (Q ₂ ) and a sine wave oscillator (OSC) connected to all delay circuits. 3. When the number of electrodes is one, between the input of the voltage follower amplifier (Q ₂ ) to which the electrode (2) is not connected, between the electrode (2) and the guard pole (3), and the coaxial cable. A capacitor (C _6b ) having a capacity equal to the sum of the distributed capacity between the inner conductor (5) and the outer conductor (6) of claim 1 is added.
The described capacitance type displacement meter. 4. A differential sampling circuit (16) with two electrodes is provided with two voltage follower amplifiers (Q ₁ ),
The output (e ₁ ) and (e ₂ ) of (Q ₂ ) are input, and the subtractor (10) that outputs the difference between them and the adder (12) that adds the outputs (e ₁ ) and (e ₂ ) A delay circuit (13) for delaying the adder output (e ₄ ), a comparator (14) for making the delay circuit output (e ₅ ) a square wave, and a sine wave oscillator (OSC) output (e _i ). The comparator (15) for making a square wave and the subtractor (10) output (e ₃ ) are analog inputs, and the output (e) of the comparator (14) is
₆ ) as the hold command input, and the output of the comparator (15) (e
Sample hold circuit (1 with ₇ ) as sample command input
The electrostatic capacitance type displacement meter according to claim 1, which comprises 1). 5. A voltage follower in which a sampling circuit with one electrode excludes the adder (12), and an input of a delay circuit (13) changes its output according to the detected capacitance. amplifier (Q ₁₎ of the output (e ₁₎ connected to claims 1 capacitance type displacement meter according. 6. An electrode section and a capacitance-voltage conversion circuit (7)
3. The capacitance-voltage conversion circuit (7) and the sampling circuit (16) are directly connected to each other and separated by a cable.
The described capacitance type displacement meter. 7. One or two cylindrical electrodes (22)
, One or two cylindrical guard poles (23) surrounding it, an outer cylinder (27) surrounding it, and insulating rings (28), (29) for electrically insulating them. ,
The capacitance type displacement meter according to claim 1, comprising a shaft (24) that slides in the electrode (22) corresponding to the displacement amount. 8. A roller-shaped electrode (32) that can be moved up and down depending on the thickness of the insulating measurement object (34), and the insulating measurement object (3).
4) Guard pole (33) surrounding the electrode part not facing
And a column (37) for supporting the roller-shaped electrode (32),
Insulating spacers (38), (39) for insulating between the electrode (32), the guard electrode (33), and the support (37) and the roller-shaped electrode (32) through the insulating DUT (34). The capacitance type displacement meter according to claim 1, further comprising a fixed roller (40).