JP2017015575A - Surface potential measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface potential measuring device capable of specifying and outputting a surface potential detection sensitivity corresponding to a malfunction of a vibrator chopping an electric field acting on a detection electrode. Displacement current generated in a detection electrode is provided with a detection electrode, a vibrator that chops an electric field between the detection electrode and the object to be measured, and a vibrator drive circuit that vibrates the vibrator. Assuming a surface potential detection device for detecting the surface potential of the object to be measured from, a sine wave oscillation signal is taken out from the vibration circuit 8 comprising the vibrator 2 and the vibrator drive circuit 7 and compared with a preset reference value. And a level determination unit 10 for specifying the level of the oscillation signal and outputting the specified level of the oscillation signal as the detection sensitivity level of the surface potential. [Selection] Figure 1

Description

  The present invention relates to a surface potential measuring apparatus including a vibrator that chops an electric field acting on a detection electrode opposed to a measurement object.

2. Description of the Related Art Conventionally, there is known a surface potential measuring device that converts an electric field between a measurement object and a detection electrode into an alternating voltage by chopping with a vibrator and detects a surface potential of an object to be measured from the voltage.
Specifically, a vibrator that is provided in the vicinity of the detection electrode and periodically opens and closes, periodically changes the electric field received by the detection electrode by opening and closing the vibrator, and signals the displacement current flowing from the detection electrode to the ground. Is detected.

In this type of surface potential measuring apparatus, when a malfunction of the vibrator occurs due to foreign matter adhering to the vibrator, the facing area between the detection electrode and the measurement object changes even if the measurement object does not change. Therefore, the current value induced in the detection electrode changes. For this reason, the detection of the surface potential may be disabled or the detection sensitivity may be reduced.
As mentioned above, when a malfunction of the vibrator occurs, if you do not notice it, you will not notice even if the surface potential of the object to be measured becomes abnormal, and you will miss the abnormal charge, causing static electricity trouble There is also.
In order to cope with such a problem, a surface potential measuring apparatus shown in Patent Document 1 is known that can automatically detect a malfunction of the vibrator and display the detection result.

This conventional surface potential measuring apparatus takes out a trapezoidal oscillation signal from an oscillation circuit composed of an oscillator and an oscillator drive circuit, and detects an operation failure of the oscillator from a change in its waveform. When the operation failure of the vibrator occurs, the trapezoidal wave gradually deteriorates in rising and falling, and the waveform is distorted. Thereafter, the oscillation signal whose waveform has changed has a small amplitude, and when the vibrator stops operating, no signal is output.
Therefore, in the above-described conventional apparatus, the trapezoidal wave extracted from the vibration circuit is compared with the amplitude threshold value, and the normal, abnormal, and failure determination is performed.

JP 2003-021656 A

In the conventional surface potential measuring device, the trapezoidal wave of the vibration circuit is used to detect the malfunction of the vibrator. However, even if the trapezoidal wave has a waveform, the amplitude hardly changes. For this reason, even if the amplitude is compared with the threshold value, it is not possible to automatically detect a malfunction of the vibrator in a range where the change in the amplitude is small even if the rise or fall changes.
For this reason, the above-described surface potential measuring device cannot be effectively used for surface potential measurement that requires measurement accuracy.
Even if an abnormality is detected based on the trapezoidal wave, since the relationship between the abnormality level and the detected value of the surface potential is unknown, it is not known how reliable the output surface potential value can be. Therefore, when the measurement accuracy is not so required, even if it is determined that the state of the vibrator is abnormal, it will continue to use the measuring device as it is and suddenly it will be in a failure state where the vibrator does not operate There was also.

  An object of the present invention is to provide a surface potential measuring device capable of specifying and outputting surface potential detection sensitivity corresponding to a malfunction of a vibrator that chops an electric field acting on a detection electrode.

The present invention includes a detection electrode, a vibrator that chops an electric field between the detection electrode and the measurement target, and a vibrator drive circuit that vibrates the vibrator, and the measurement target is obtained from a displacement current generated in the detection electrode. It is assumed that the surface potential detecting device detects the surface potential.
A first invention is based on the surface potential measuring device described above, and a sine wave oscillation signal is extracted from a vibration circuit including the vibrator and a vibrator driving circuit, and the oscillation is compared with a preset reference value. A level determination unit is provided that specifies a signal level and outputs a surface potential detection sensitivity level corresponding to the specified oscillation signal level.

  According to a second aspect of the present invention, there is provided a potential correction unit that corrects the surface potential specified based on the displacement current generated in the detection electrode according to the detection sensitivity level specified by the level determination unit, and outputs the correction value. It is characterized by having.

According to the first aspect of the present invention, the detection sensitivity level of the surface potential can be easily specified by extracting a sine wave oscillation signal whose amplitude correlates with the potential detection sensitivity from the vibration circuit. As a result, the degree of malfunction of the vibrator can be determined, and the reliability of the surface potential measurement can be judged.
It is also possible to calculate an accurate surface potential value according to the output detection sensitivity level.

In addition, since the level of malfunction of the transducer corresponding to the above detection sensitivity level is also known, device maintenance such as replacement of the transducer before the transducer becomes almost inoperable, which is conventionally displayed as a failure, is maintained. Will be able to. Therefore, it can be prevented that the vibrator is broken and suddenly the potential detection becomes impossible.
That is, the detection sensitivity level can be used as a guideline for performing maintenance. As a result, the vibrator can be maintained at an appropriate timing, and the maintenance need not be performed more than necessary.

According to the second invention, since the surface potential value is corrected according to the potential detection level, the correct surface potential value of the measurement target can be automatically output even if the transducer malfunctions. Can do.
In particular, when an alarm device is operated based on the surface potential signal detected by the surface potential measuring device or when another device is controlled, even if a malfunction of the vibrator occurs, It is useful to output a true surface potential value.

It is a block diagram of one embodiment of this invention. It is a graph which shows an oscillation signal.

An embodiment of the present invention will be described with reference to FIG.
In this apparatus, a polarity discriminating circuit 4 for discriminating the polarity of a potential detection signal output from the detection electrode 1 is connected to a detection unit 3 comprising a detection electrode 1 and a vibrator 2 provided in a sensor case (not shown). Has been. The polarity discriminating circuit 4 is connected to a potential correcting unit 5, and the potential correcting unit 5 is further connected to a potential display unit 6 for displaying a surface potential value of a measurement object measured by the surface potential device. Yes.

On the other hand, a vibrator drive circuit 7 for driving the vibrator 2 is connected to the vibrator 2, and the vibrator 2 and the vibrator drive circuit 7 constitute a vibration circuit 8.
A level determination unit 10 is connected to the vibration circuit 8 via an amplifier circuit 9, and a sensitivity level display unit 11 that displays the detection sensitivity level determined by the level determination unit 10 is connected to the level determination unit 10. ing.
In this embodiment, the vibrator driving circuit 7 is provided outside the sensor case that houses the detection unit 3. However, the vibrator driving circuit 7 is housed in the sensor case together with the detection unit 3. May be.

The principle of detecting the surface potential of the surface potential measuring apparatus of this embodiment is the same as that of the conventional apparatus described above, but will be briefly described below.
When the vibrator 2 is operated by the vibrator driving circuit 7, an alternating electric field corresponding to the surface potential of the measurement target (not shown) acts on the detection electrode 1, and a potential detection signal is output. This potential detection signal is discriminated between positive and negative polarities by the polarity discriminating circuit 4 and converted into a DC voltage for each positive and negative.

Note that a vibration circuit 8 is connected to the polarity determination circuit 4 so that a sine wave oscillation signal by self-excited oscillation of the vibrator 2 and the vibrator drive circuit 7 is inputted. The polarity discriminating circuit 4 detects the opening / closing timing of the vibrator 2 from the oscillation signal, and discriminates the positive / negative polarity of the potential detection signal.
The potential detection signal converted into the DC voltage is corrected by the potential correction unit 5 and the corrected positive and negative surface potential values are displayed on the potential display unit 6 as will be described later.
However, a trapezoidal wave may be extracted from the vibration circuit 8 and input to the polarity determination circuit 4. The polarity discriminating circuit 4 can also detect the opening / closing timing of the vibrator 2 based on the trapezoidal wave and discriminate the polarity of the potential detection signal.

Further, the sine wave oscillation signal is also input to the amplifier circuit 9 connected to the vibration circuit 8, and the amplified oscillation signal is input to the level determination unit 10.
Further, the level determination unit 10 specifies the level by comparing the amplitude of the input oscillation signal with a preset reference value.
The reference value is the amplitude A of the oscillation signal output from the vibration circuit 8 when the vibrator 2 is operating normally. A sine wave that is an oscillation signal having an amplitude A, which is the reference value, is indicated by a solid line in FIG. 2. While the vibrator 2 is operating normally, the oscillation signal indicated by the solid line is transmitted from the oscillation circuit 8. Is output.

However, when a malfunction of the vibrator 2 occurs for some reason, for example, an oscillation signal having an amplitude B smaller than the amplitude A is output from the vibration circuit 8 as indicated by a broken line in FIG.
When the oscillation signal having the reduced amplitude is input, the level determination unit 10 compares the amplitude B with the amplitude A of the reference value to specify the level of the amplitude B. In this embodiment, the numerical value indicated by the ratio [%] of the amplitude B to the amplitude A is used as the level of the oscillation signal, and this is displayed on the sensitivity level display unit 11 as the detection sensitivity level.

The detection sensitivity level is a level of the detection sensitivity of the surface potential detected by the detection electrode 1, and this detection sensitivity level is a value having a correlation with the level of the oscillation signal.
The reason is as follows.
In the surface potential measuring apparatus of this embodiment, the exposed area of the detection electrode 1 with respect to the measurement object is changed by opening and closing the vibrating vibrator 2.
For this reason, when an operation failure of the vibrator 2 occurs and the vibrator 2 does not fully open, the area of the detection electrode 1 facing the object to be measured is reduced, and the current induced in the detection electrode is reduced. That is, if the malfunction of the vibrator 2 occurs and the level of the oscillation signal decreases, the absolute value of the potential detection signal should also decrease. Therefore, the level of the oscillation signal specified by the level determination unit 10 can be output as the potential detection sensitivity level. Thus, it has been confirmed by experiments that the level of the oscillation signal correlates with the detection sensitivity level.
In addition, when the operation failure of the vibrator 2 occurs and the opening thereof becomes small, the amplitude of the sine wave oscillation signal becomes small, and it has been confirmed through experiments that this amplitude and the operation state of the vibrator 2 are correlated. Yes.

If the potential detection sensitivity level is displayed on the sensitivity level display unit 11 as described above, the user can know the detection sensitivity of the detection electrode 1 and know the operating state of the vibrator 2 by the display. be able to. When the detection sensitivity level is lowered, maintenance such as exchanging the vibrator 2 can be considered.
If the detection sensitivity level does not decrease so much, the device can be used as it is for a while, and when the detection sensitivity level decreases, maintenance is performed. You can also

On the other hand, as described above, the potential detection signal output from the detection electrode 1 is discriminated by the polarity discriminating circuit 4 and converted into a DC voltage signal, and then corrected by the potential correcting unit 5. A method of correcting the potential detection signal input from the polarity discriminating circuit 4 by the potential correcting unit 5 will be described. The signal input from the polarity discriminating circuit 4 to the potential correction unit 5 is a DC voltage signal. Here, the DC voltage signal is also referred to as a potential detection signal.
The potential correction unit 5 receives the potential detection signal from the polarity determination circuit 4 and the detection sensitivity level from the level determination unit 10.

The detection sensitivity level input to the potential correction unit 5 is a value specified from the amplitude of the sine wave oscillation signal as described above.
For example, when the oscillation signal input to the level determination unit 10 is 60 [%] of the amplitude A, which is the reference value, as shown by the broken line in FIG. The value is 60 [%] compared to when there is no problem in the operation of the vibrator 2 at all. Therefore, the potential correction unit 5 corrects the value of the 60% signal to 100% and causes the potential display unit 6 to display the surface potential value.
In this way, even if the operation failure of the vibrator 2 occurs and the potential detection sensitivity decreases, the corrected surface potential value is displayed on the potential display unit 6.

In this embodiment, the surface potential value corrected based on the detection sensitivity level that changes according to the operating state of the vibrator 2 is output. However, the potential display unit is not provided, and the potential display is performed. The unit 6 may display an uncorrected surface potential value.
In that case, depending on the level of malfunction of the vibrator 2, a surface potential value having an absolute value smaller than the true value is displayed on the potential display unit 6, but as described above, the sensitivity level display unit If the detection sensitivity level is displayed at 11, the surface potential value displayed on the potential display unit 6 is found to be smaller than the true surface potential value. Therefore, it is possible to determine how much the displayed surface potential value should be trusted.
Furthermore, it is possible to predict a true surface potential value based on the detection sensitivity level displayed on the sensitivity level display unit 11.

Further, when the detection sensitivity level value output from the level determination unit 10 or the surface potential value output from the potential correction unit 5 is input to the alarm device and the detection sensitivity level falls below a set value, An alarm may be issued when the potential value exceeds a set value.
Furthermore, if the surface potential value corrected from the potential correction unit 5 is input to another device controlled based on the surface potential value of the measurement object, it is assumed that the operation failure of the vibrator 2 has occurred. Can also be controlled based on the true surface potential value.
The level determination unit 10 compares the detection sensitivity level output from the level determination unit 10 with a threshold value and roughly classifies the detection sensitivity level as, for example, conventional normality, abnormality, or failure, and detects the level. You may make it display with a sensitivity level. Further, based on the above rough classification, an alarm can be issued or a caution lamp can be turned on.

  The present invention can be applied to various forms of surface potential measuring devices including a vibrator that chops an electric field acting on a detection electrode.

DESCRIPTION OF SYMBOLS 1 Detection electrode 2 Vibrator 5 Electric potential correction part 6 Electric potential display part 7 Vibrator drive circuit 8 Vibration circuit 10 Level determination part 11 Sensitivity level display part

Claims (2)

A sensing electrode;
A vibrator for chopping an electric field between the detection electrode and a measurement object;
A vibrator driving circuit for vibrating the vibrator,
In the surface potential detection device for detecting the surface potential of the measurement object from the displacement current generated in the detection electrode,
A sine wave oscillation signal is extracted from the oscillation circuit consisting of the transducer and the transducer drive circuit, and the level of the oscillation signal is specified in comparison with a preset reference value, and this oscillation signal level is supported. A surface potential measuring device including a level determination unit that outputs a detection sensitivity level of surface potential. The electric potential correction | amendment part which correct | amends the surface potential specified based on the displacement current which arises in the said detection electrode according to the detection sensitivity level specified by the said level determination part, and outputs the correction value to Claim 1 is provided. The surface potential measuring device described.

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