JPS626164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitive displacement meter, and is intended to improve the previously proposed displacement meter.

Figure 1 shows the basic measurement principle of a capacitive displacement meter. If the area of the electrode plate is s, the electrode plate spacing is d, and the dielectric constant is ε, then the capacitance C is C=(ε・
s)/d. As a capacitive displacement meter using this basic principle, published patent publication No. 54-41764,
There are 107354 (1983) and 110655 (1982), but they have the following drawbacks. (1) Measurement distance is small. At most, it is about 10mm. (2) The maximum wiring distance from the detector to the amplifier, etc. is approximately 5 m. (3) Affected by stray capacitance between wiring and ground. (4) Measurement cannot be performed if the object to be measured is at high temperature.

The present inventor previously proposed a capacitive displacement meter as shown in FIG. 2 which solves these drawbacks. The present invention relates to an improvement of this method. As shown in FIG. 2, the capacitive displacement meter includes a detector 5, a high frequency oscillator 10, a charge amplifier 11, and a filter 1.
2, a detection amplifier 13, and a linearizer 14. The detector 5 has two electrode plates 1 and 2.
It is composed of a shield case 3, a shield plate 4 between electrode plates, and the electrode plates 1 and 2 are arranged to face the object to be measured 20.

The electrode plate 1 of the detector 5 is connected to a charge amplifier 11, and the electrode plate 2 is connected to a high frequency oscillator 10. Shield cases 3 and 4 are grounded. The constant frequency sine wave, triangular wave, or pulsed high frequency current supplied from the high frequency oscillator 10 is
It is supplied from electrode plate 2 to electrode plate 1 . The magnitude of the high frequency current is approximately proportional to the distance l between the detector 5 and the object to be measured. Of course, it goes without saying that it is also proportional to the area of the electrode plate. The magnitude of this high frequency current is detected as the amount of charge by the charge amplifier 11,
amplified. A filter 12 removes noise from the amplified signal, and a detection amplifier 13 amplifies and rectifies the signal to convert it into direct current. Furthermore, the linearizer 14 obtains an output voltage/current proportional to the measurement distance l. It was previously proposed that the distance Δl between the electrode plates 1, 2 and the shield cases 3, 4 is important in adjusting the measurement distance and measurement sensitivity in this capacitive displacement meter.

The present invention relates to an improvement of the detector 5.
FIG. 3 shows the structure of the detector 5 when the shield plate 4 between the electrode plates is removed. FIG. 6 shows the distance characteristics with and without the shield plate 4. Curve a in FIG. 6 shows the characteristics with the shield plate 4 (detector in FIG. 2), and curve b in FIG. 6 shows the characteristics without the shield plate 4. Note that the distance characteristic is the output of the detection amplifier 13. The measurement distance and sensitivity can be changed depending on the presence or absence of the shield plate 4. FIG. 4 shows the structure of a detector 5 in which the shield plate 4 is made shorter by a length D than the shield plate shown in FIG.

The distance characteristic of the detector in Fig. 4 is the curve c in Fig. 6.
It is a characteristic of FIG. 5 shows the structure of the detector 5 when the shield plate 4 is removed in a triangular shape, and even with this shape, the distance characteristics and sensitivity can be improved.

That is, if the area S of the electrode plates 1 and 2 and the thickness L of the electrode plates are constant, the electrode plates 1 and 2 in the shield case 3
By controlling the capacitance generated between the two using the shield plate 4, distance characteristics and sensitivity can be improved. In determining distance characteristics and sensitivity, electrode plate 1,
It goes without saying that the area S of 2 is dominant. Furthermore, it is also somewhat effective to improve the distance characteristics and sensitivity by changing the thickness L of the electrode plates 1 and 2.

As described above, the area of the metal plate shielding between the electrode plates can be taken as an operating parameter when determining the optimal range of distance characteristics and sensitivity when measuring the displacement of an object. As one means of changing the area of the shield plate between the electrode plates,
When this is done discretely, there is a means shown in FIG.

If the area of the shield plate is to be changed continuously, the value of D shown in FIG. 4a is continuously changed by, for example, making the shield plate movable up and down. A known screw mechanism or fluid pressure mechanism can be used as a means for raising and lowering the shield plate.

In improving the sensitivity, as shown in FIG. 2, the sensitivity is better when the high frequency current/voltage supplied from the high frequency oscillator 10 to the electrode plate 2 is a pulse rather than a sine wave.

As for the waveform at that time, a rectangular wave is better in increasing sensitivity.

As described above, the present invention can improve distance characteristics and sensitivity by changing the shape of the shield plate 4. Furthermore, sensitivity can be improved in high frequency pulse oscillation signals.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram showing the basic principle of a capacitance type displacement meter, Figure 2 is a block diagram showing the configuration of the capacitance type displacement meter proposed earlier, and Figure 3.
4 and 5 are diagrams showing the detector of the present invention, in which a is a cross-sectional view, b is a bottom view, and c in FIG. 5 is a side view,
FIG. 6 is a chart showing distance characteristics. 1: Electrode plate, 2: Electrode plate, 3: Shield case, 4: Shield plate, 5: Detector, 10: High frequency oscillator, 11: Charge amplifier, 12: Filter, 13: Detection amplifier, 14: Linearizer,
15: Earth, 20: Object to be measured.

Claims (1)

[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. An AC oscillator, an amplifier consisting of a charge amplifier and a voltage amplifier that convert the capacitance between the other electrode plate and the object to be measured into voltage, and a converter that linearizes the output from the amplifier. In the capacitive displacement meter, the area of the shield plate provided between the pair of electrode plates is configured to be changed discretely or continuously depending on the distance range in which displacement is to be measured and the required detection sensitivity. Capacitive displacement meter.