JP3518809B2 - Surface potential detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric field between an object to be measured and a detection electrode, which is chopped by a vibrator to convert the electric field into an AC voltage. The present invention relates to a surface potential detecting device that detects a surface potential of an object. 2. Description of the Related Art Conventionally, an electric field between an object to be measured and a detection electrode is chopped by a vibrator to be converted into an AC voltage, and the surface potential of the object to be measured is detected from the voltage. A well-known external-circuit-type tuning fork-type surface potential sensor shown in FIG. 1, a circuit-incorporating-type tuning-fork-type surface potential sensor shown in FIG. 2, and a sound-piece-type surface potential sensor shown in FIG. A tuning fork type surface potential sensor externally attached to a circuit shown in FIG. 1 is provided in a box-shaped sensor case 2 having a detection hole 1.
A vibrator driving circuit 7 that incorporates a tuning fork vibrator 4 provided with a pair of piezoelectric elements 3, a detection electrode 5, and a preamplifier 6 and supplies power to the pair of piezoelectric elements 3 to vibrate the tuning fork vibrator 4; 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 the sensor case 2 to reduce the size of the sensor itself. In this sensor, a line of electric force from an object to be measured toward the detection electrode 5 through the detection hole 1 is chopped by the vibration of the tuning-fork vibrator 4 and is taken out as an AC voltage by the preamplifier 6 to the outside. [0004] The tuning-fork type surface potential sensor with a built-in circuit shown in FIG.
The sensor case 2 incorporates an IC 8 in which an AC amplifier circuit for amplifying the output of the preamplifier 6 and a synchronous detection rectifier circuit for rectifying the output are rectified into a DC voltage from the preamplifier 6, and an output adjustment volume 9. And output from the connector 10. The sound piece type surface potential sensor shown in FIG. 3 uses a sound piece type vibrator 4a instead of the tuning fork type vibrator 4, and uses a preamplifier 6, an AC amplifier 11, a synchronous detection rectifier circuit 12, a DC amplifier 13 and An IC 15 in which a child drive circuit 7 and a regulator 14 are mixed is built in the sensor case 2. However, this type of surface potential sensor is generally vulnerable to impact or the like, and the sensor case 2
Since it is necessary to provide the detection hole 1 in the
It is inevitable that powder, dust, solvent, and the like enter the sensor case 2 from the sensor case 2, which hinders the vibration of the tuning-fork vibrator 4 or the vibrating reed vibrator 4 a, or the vibration of the vibrator is improper due to an impact. Or the transducer may be damaged, making detection impossible or detection abnormal. However, there is no means for notifying (displaying) this. SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface potential detecting device capable of self-diagnosing the presence / absence of a vibration failure of a vibrator and notifying (displaying) when the detection becomes impossible or abnormal. To provide. [0008] The present invention provides a detection electrode,
A vibrator for chopping the electric field between the detection electrode and the device under test is built in a sensor case having a detection hole,
In a surface potential detecting device that vibrates a vibrator by a vibrator driving circuit and detects a surface potential of an object to be measured from an AC voltage generated from a detection electrode, a polarity discrimination that determines a positive or negative polarity of the AC voltage generated from the detection electrode. Circuit, an amplifier circuit for amplifying an oscillation signal of self-excited oscillation by the oscillator and the oscillator drive circuit, a level of the amplified oscillation signal, a normal level, an abnormal level in which the oscillation signal is attenuated and deformed, A comparator that can determine the three levels of the failure level with no oscillation signal and a digital display that displays the results of the three levels of self-excited oscillation and that displays the detected surface potential together with the polarity determined by the polarity determination circuit. And a display device. 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 an AC amplifying circuit 16 outside the sensor case 2, and then a positive / negative polarity is determined by a polarity determining circuit 17.
The positive and negative DC voltages are taken out by the buffer circuit 18 and the digital display 19 digitally displays the electric potential together with the positive and negative polarities. On the other hand, an oscillation signal by self-excited oscillation of the vibrator 4 and the vibrator drive circuit 7 is amplified by an amplifier circuit 20 and then compared with a threshold value by a comparator 21. This oscillation signal is a trapezoidal wave as shown in FIG. 5A when the oscillation of the oscillator 4 is normal, that is, when the self-excited oscillation is normal.
When the oscillation of the vibrator 4 becomes abnormal and the self-excited oscillation is attenuated, the trapezoidal wave becomes an attenuated waveform as shown in FIG. 4B, and when the vibrator 4 stops vibrating. Becomes no signal as shown in FIG. Therefore, a higher threshold SH1 and a lower threshold SH2 are given to the comparator 21, and the comparator 21 is normal when the output level from the amplifier circuit 20 is higher than the threshold SH1, and normal when SH1 and SH2. In this case, a comparison can be made in three stages: abnormal when the value is less than SH2, and failure when the value is lower than SH2. Then, the output of the comparator 21 is output to the digital display 19, and the digital display 19 performs three-stage identification indicating whether the self-excited oscillation is normal, abnormal, or failure. FIG. 6 shows that a self-diagnosis display light-emitting element (light-emitting diode) 22 is provided on the outer surface of the sensor case 2 so that the above-described self-diagnosis result can be displayed on the sensor case 2 of the surface potential sensor. The normal state and the failure can be identified and displayed by turning off and on the light. In addition,
On the outer surface of the sensor case 2, there are also provided 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 that enable the sensitivity to be adjusted in two stages. As described above, according to the present invention, a self-diagnosis of the presence or absence of a vibration failure of the vibrator is performed, and when the detection becomes impossible or the detection becomes abnormal, the fact is notified (displayed). )can do.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a schematic configuration of a conventional tuning-fork type surface potential sensor externally attached to a circuit. 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 according to the present invention. 5A and 5B are waveform diagrams of oscillation signals generated by self-excited oscillation of a vibrator and a vibrator drive circuit, where FIG.
(C) is a time of failure. 6A and 6B show an example of displaying a self-diagnosis result on a sensor case of a surface potential sensor, wherein FIG. 6A is a top view, FIG. 6B is a side view, and FIG. 6C is a bottom view. [Description of Signs] 1 Detector hole 2 Sensor case 3 Piezoelectric element 4 Tuning fork vibrator 4a Resonator vibrator 5 Detection electrode 6 Preamplifier 7 Vibrator drive circuit 8 IC 9 Output adjustment volume 10 Connector 11 AC amplifier 12 Synchronous detection rectification Circuit 13 DC amplifier 14 Regulator 15 IC 16 AC amplifying circuit 17 Polarity discriminating circuit 18 Buffer circuit 19 Digital display 20 Amplifying circuit 21 Comparator 22 Self-diagnosis display light emitting element 23 Sensitivity adjustment button 24 Zero adjustment button 25 Sensitivity display light emitting element 26 Light emitting element for zero adjustment display

Claims (1)

(57) [Claim 1] A detecting electrode and a vibrator for chopping an electric field between the detecting electrode and the object to be measured are built in a sensor case having a detecting hole, and the vibrator is provided. In a surface potential detection device that detects the surface potential of the device under test from the AC voltage generated from the detection electrode, a polarity determination circuit that determines the positive or negative polarity of the AC voltage generated from the detection electrode. A failure amplifying circuit for amplifying an oscillation signal of self-excited oscillation by the oscillator and the oscillator drive circuit; and a level of the amplified oscillation signal, a normal level, and an abnormal level where the oscillation signal is attenuated and deformed. And a comparator for determining a failure which can be determined in three stages of a failure level having no oscillation signal, and displaying the determination results of the three stages of self-excited oscillation, and detecting the detected surface potential by the polarity determination circuit. Surface potential detecting apparatus characterized by comprising a digital display for the polar digital display with.