JP2003021656A - Surface potential detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface potential detection device capable of performing self-diagnosis of existence of a damage by vibration of a vibrator, and reporting (displaying) detection incapability or detection abnormality if it occurs. SOLUTION: This device is equipped with a fault determination circuit for taking out an oscillation signal by the vibrator 4 and a vibrator driving circuit 7, and comparing its level with a threshold by a comparator 21, to thereby determine as an abnormality or a fault in the case below the threshold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface potential detection in which an electric field between an object to be measured and a detection electrode is chopped by a vibrator and converted into an AC voltage, and the surface potential of the object to be measured is detected from the voltage. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, a surface potential sensor for chopping an electric field between an object to be measured and a detection electrode with an oscillator to convert it into an AC voltage and detecting the surface potential of the object to be measured from the voltage is shown in FIG. The external circuit type tuning fork type surface potential sensor shown in FIG. 2, the circuit built-in tuning fork type surface potential sensor shown in FIG. 2 and the tuning piece type surface potential sensor shown in FIG. 3 are well known.

The external circuit type tuning fork type surface potential sensor shown in FIG. 1 is provided in a box-shaped sensor case 2 having a detection hole 1.
A tuning fork type vibrator 4 having a pair of piezoelectric elements 3 attached thereto, a detection electrode 5 and a preamplifier 6 are built-in, and a vibrator driving circuit 7 for feeding the pair of piezoelectric elements 3 to vibrate the tuning fork type vibrator 4 and the preamplifier 6 AC amplifier circuit (not shown) that amplifies the output of
And a synchronous detection rectifier circuit (not shown) that rectifies the output
Is provided outside of the sensor case 2 to reduce the size of the sensor itself. In this sensor, the lines of electric force from the object to be measured, which are directed to the detection electrode 5 through the detection hole 1, are chopped by the vibration of the tuning fork type vibrator 4 and taken out as an AC voltage by the preamplifier 6.

The built-in circuit type tuning fork type surface potential sensor shown in FIG. 2 is a vibrator driving circuit for vibrating the tuning fork type vibrator 4,
The sensor case 2 has a built-in IC 8 that mixes an AC amplification circuit that amplifies the output of the preamplifier 6 and a synchronous detection rectification circuit that rectifies the output, rectifies the AC voltage from the preamplifier 6 into a DC voltage, and outputs the output adjustment volume 9 Is adjusted so that it can be output from the connector 10.

In the sound piece type surface potential sensor shown in FIG. 3, a sound piece type vibrator 4a is used in place of the tuning fork type vibrator 4, and a preamplifier 6, an AC amplifier 11, a synchronous detection rectifier circuit 12, a DC amplifier 13 and a vibration are used. The IC 15 in which the slave drive circuit 7 and the regulator 14 are mixed is built in the sensor case 2.

[0006]

However, this type of surface potential sensor is generally weak against impact and the sensor case 2
Since it is necessary to provide the detection hole 1 in the
It is inevitable that powder, dust, solvent, etc. will enter the sensor case 2 from them, and these will hinder the vibration of the tuning fork type vibrator 4 or the tuning piece type vibrator 4a, or the vibration of the vibrator will be disturbed by a shock. However, there was a case where detection was impossible or abnormal detection due to damage to the vibrator or the like, but there was no means for notifying (displaying) it.

An object of the present invention is to provide a surface potential detecting device capable of self-diagnosing the presence or absence of a vibration disturbance of a vibrator, and notifying (displaying) the fact when a detection failure or a detection failure occurs. To provide.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a detection electrode,
A vibrator for chopping the electric field between the detection electrode and the object to be measured is built in a sensor case having a detection hole,
In a surface potential detection device that oscillates the oscillator by the oscillator drive circuit and detects the surface potential of the object to be measured from the AC voltage generated from the detection electrode, the oscillation signal from the oscillator and the oscillator drive circuit is extracted and its level is output. Is compared with a threshold value by a comparator, and a failure determination circuit for determining an abnormality or a failure when it is less than or equal to the threshold value is provided.

The failure judgment circuit includes an amplifier circuit for amplifying an oscillation signal generated by the oscillator and the oscillator drive circuit, a level of the amplified oscillation signal, a normal level, and an abnormal level in which the oscillation signal is attenuated and deformed. It is preferable to configure with a comparator that can judge in three stages of failure level with no oscillation signal.

The judgment result of the failure judgment circuit may be displayed on a display that digitally displays the detected surface potential, or may be displayed by a light emitting element attached to the sensor case.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 4 shows an embodiment of the present invention applied to the tuning fork type surface potential sensor as shown in FIG. The AC voltage output from the preamplifier 6 in the sensor case 2 is amplified by the AC amplification circuit 16 outside the sensor case 2, and then the polarity determination circuit 17 determines positive and negative polarities.
Positive and negative polarities are taken out as DC voltages by the buffer circuit 18, and the digital display 19 digitally displays the potentials with positive and negative polarities.

On the other hand, the oscillation signal generated by the self-excited oscillation of the oscillator 4 and the oscillator drive circuit 7 is amplified by the amplifier circuit 20 and then compared with the threshold value by the comparator 21. This oscillation signal is a trapezoidal wave as shown in FIG. 5A when the vibration of the oscillator 4 is normal, that is, when the self-excited oscillation is normal.
When the vibration of the oscillator 4 becomes abnormal and the self-excited oscillation is attenuated, a trapezoidal wave becomes a damped attenuation waveform as shown in (b) of the figure, and when the oscillator 4 stops vibrating. Shows no signal as shown in FIG.

Therefore, the comparator 21 is given a higher threshold value SH1 and a lower threshold value SH2, and the comparator 21 is normal when the output level from the amplifier circuit 20 is higher than the threshold value SH1, and SH1 and SH2. It is possible to make a three-stage comparison judgment of abnormality when the value is between and, and failure when the value is lower than SH2. However, in the case of this example, the abnormality is treated as a failure, and the output of the comparator 21 is divided into two stages, that is, normal and failure, and the digital display 19
Is output to the digital display 19, and the digital display 19 is used to identify and display normality or failure. Of course, it is also possible to carry out three-level identification display of normal, abnormal, and failure. Also, an abnormality or failure may be notified by an alarm sound.

In FIG. 6, a self-diagnosis display light emitting element (light emitting diode) 22 is attached to the outer surface of the sensor case 2 so that the above self-diagnosis result can be displayed on the sensor case 2 of the surface potential sensor. The light is turned off and turned on so that normality and failure can be identified and displayed. Besides this,
A sensitivity adjustment button 23, a zero adjustment button 24, a sensitivity display light emitting element 25, and a zero adjustment display light emitting element 26 are provided on the outer surface of the sensor case 2 so that the sensitivity can be adjusted in two steps.

[0016]

As described above, according to the present invention, it is possible to self-diagnose the presence / absence of a vibration failure of a vibrator, and to notify (display) the fact when a detection failure or a detection abnormality occurs. You can

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a conventional external fork type tuning fork type surface potential sensor.

FIG. 2 is a perspective view showing a schematic configuration of a conventional tuning-fork type surface potential sensor with a built-in circuit.

FIG. 3 is a perspective view showing a schematic configuration of a conventional sound piece type surface potential sensor.

FIG. 4 is a block diagram showing an example of a surface potential detecting device of the present invention.

FIG. 5 is a waveform diagram of an oscillation signal generated by self-excited oscillation between a vibrator and a vibrator drive circuit. (A) shows a normal state, (b) shows an abnormal state,
(C) is at the time of failure.

6A and 6B show examples of displaying a self-diagnosis result on a sensor case of a surface potential sensor, FIG. 6A is a top view, FIG. 6B is a side view, and FIG. 6C is a bottom view.

[Explanation of symbols]

1 detection hole 2 sensor case 3 Piezoelectric element 4 Tuning fork type transducer 4a Sound piece type transducer 5 detection electrodes 6 preamplifier 7 Transducer drive circuit 8 IC 9 Output adjustment volume 10 connectors 11 AC amplifier 12 Synchronous detection rectifier circuit 13 DC amplifier 14 Regulator 15 IC 16 AC amplifier circuit 17 Polarity discrimination circuit 18 Buffer circuit 19 Digital display 20 amplifier circuit 21 Comparator 22 Light emitting device for self-diagnosis display 23 Sensitivity adjustment button 24 Zero adjustment button 25 Light-emitting element for sensitivity display 26 Light-emitting element for zero adjustment display

Claims (4)

[Claims] 1. A detection electrode and a vibrator for chopping an electric field between the detection electrode and an object to be measured are built in a sensor case having a detection hole, and the vibrator is vibrated by a vibrator driving circuit. In a surface potential detecting device for detecting the surface potential of an object to be measured from an AC voltage generated from a detection electrode, an oscillation signal from the oscillator and the oscillator drive circuit is taken out and its level is compared with a threshold value by a comparator, A surface potential detecting device comprising a failure determination circuit for determining an abnormality or a failure in the following cases. 2. A failure determination circuit, an amplifier circuit for amplifying an oscillation signal by a vibrator and a vibrator drive circuit, a level of the amplified oscillation signal is a normal level, and an abnormal level in which the oscillation signal is attenuated and deformed. 2. The surface potential detecting device according to claim 1, further comprising: a comparator capable of making a three-level judgment of a failure level with no oscillation signal. 3. The surface potential detecting device according to claim 1, wherein the judgment result of the failure judging circuit is displayed on a display for digitally displaying the detected surface potential. 4. The surface potential detecting device according to claim 1, wherein the determination result of the failure determining circuit is displayed by a light emitting element attached to the sensor case.