JPS6232370A - Detecting device for surface potential - Google Patents

Abstract

PURPOSE:To enable the measurement of not only the absolute value of a surface potential but also the polarity by comparing the phase of the output signal of an oscillation circuit with the phase of the output signal from a detecting electrode and by providing the polarity discriminating means to discriminate the polarity of surface potential. CONSTITUTION:The AC signal from a detecting electrode 23 is taken out of AC amplifier circuit 25, phase-shifted 32, waveform-shaped 33 and given to a logic circuit 35. On the other hand the output of a tuning fork oscillation circuit 27 is given to the circuit 35 with its waveform being shaped by the waveform shaping circuit 34 of another part. The circuit 35 compares the phase of the signal given from the circuits 33, 34 and discriminates the polarity of the surface potential. The polarity can be known by comparing the phase of the output signal of the circuit 27 with the phase of the AC signal from the electrode 23 by the circuit 35 because the phase of the AC output of a vibrating capacity capacitor becoming at the same phase or reverse phase according to the polarity of surface potential for the phase of the driving input of a piezoelectric tuning fork 21.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is directed to the pressure '1Rff! This invention relates to an improvement of a surface potential detection device called a photocapacitive type using a moving element.

[Prior Art] FIG. 8 is a schematic block diagram showing an example of a conventional surface potential detection device. Here, a capacitive surface potential detection device using a piezoelectric tuning fork 1 as a piezoelectric vibrator is shown.

The piezoelectric tuning fork 1 is excited by a tuning fork oscillation circuit 2. Further, a detection electrode 3 constituting a vibration capacitance capacitor 3A is attached to the piezoelectric tuning fork 1, and when the detection electrode 3 is vibrated by the piezoelectric tuning fork 1, a detection electrode 3 is formed between the detection electrode 3 and the surface of the object to be measured. Outputs a signal according to the change in capacitance. Detection electrode 3
The output signal is given to a surface potential detection signal processing section constituted by an AC amplifier circuit 4 and an output circuit 5. That is, the output signal of the detection electrode 3 is applied to the AC amplifier circuit 4, amplified, and taken out from the output circuit 5.

FIG. 9 is a specific electrical circuit diagram of the conventional surface potential detection device shown in FIG. 8. Pressure! ! The tuning fork 1 is excited by a tuning fork oscillation circuit composed of an operational amplifier 12. The output from the detection electrode 3 is applied to the gate of the field effect transistor 13. The field effect transistor 13 converts the output impedance of the detection electrode 3 into a low impedance.

The source output of the field effect transistor 13 is given to the AC amplifier circuit 4 via the coupling capacitor 14.
This signal is applied to one input terminal of 6. The rectifier circuit is composed of the operational amplifier 16, diodes 17, 18, etc., and converts the input alternating current signal into direct current. Therefore, an output signal corresponding to the surface potential of the surface to be measured is output as a DC potential.

[Problems to be Solved by the Invention] Incidentally, depending on the surface to be measured, the polarity of the surface potential changes from moment to moment. However, the conventional surface potential detection device described above can only know the absolute value of the surface potential, but cannot know its polarity.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a surface potential detection device Wl that is capable of determining not only the absolute value of a surface potential but also its polarity.

[Means for Solving the Problems] A surface potential detection device of the present invention includes a piezoelectric vibrator, an oscillation circuit for driving the piezoelectric vibrator, and a detection electrode attached to the piezoelectric vibrator. . It also includes a surface potential detection signal processing section that processes the output signal from the detection N8i and outputs a signal corresponding to the potential of the surface of the measurement target. The process up to this point is the same as the conventional vibration-impingement type surface potential detection device.

Further, the device of the present invention has a characteristic configuration including a polarity determining means for comparing the phase of the output signal derived from the detection electrode and the phase of the output signal of the oscillation circuit to determine the polarity of the surface potential. I'm here.

[Function] In the vibrating capacitive surface potential detection device, the phase of the AC output of the vibrating capacitor output from the detection electrode is based on the polarity of the surface potential with respect to the phase of the output of the oscillation circuit for driving the piezoelectric tuning fork. They will be in phase or out of phase depending on. Therefore,
In this invention, the phase of the AC output signal derived from the detection electrode,
By installing a polarity determining means that compares the phase of the output signal of the oscillation circuit for driving the piezoelectric tuning fork and thereby determines the polarity of the surface potential, the output signal according to the polarity of the surface potential can be determined. , can be extracted separately from a signal corresponding to the absolute value of the surface potential.

[Description of Embodiment] FIG. 1 is a schematic block diagram of a surface potential detection device according to an embodiment of the present invention. Here, as in the conventional surface potential detection device, the output of the detection electrode 23 constituting the oscillating capacitance capacitor is given to the surface potential detection signal processing section 24. The surface potential detection processing section 24 includes an AC amplifier circuit 25 and an output circuit 26. Further, the detection electrode 23 is attached to a piezoelectric tuning fork 21 as a piezoelectric vibrator, and is excited by the pressure II tuning fork 21G, t and the tuning fork oscillation circuit 27. Up to this point, the configuration is similar to that of a conventional surface potential detection device.

The special feature of this embodiment is that *gender determination means 31 is provided. , the polarity determining means 31 is the AC amplifier circuit 2
5, a waveform shaping circuit 33 that shapes the output waveform from the phase shifting circuit 32, and an h-cross oscillation circuit 2.
7, and a logic circuit 35 that compares the phases of the output signals of both waveform shaping circuits 33 and 34.

In the surface potential detection device shown in FIG.
The phase is shifted in the J circuit 32, the waveform is shaped in the waveform shaping circuit 33, and the signal is applied to the logic circuit 35. On the other hand, the output of the tuning fork oscillation circuit 27 is waveform-shaped by one of the waveform shaping circuits 34 and is applied to the C logic circuit 35. The logic circuit 35 compares the phases of the signals given from both waveform shaping circuits 33 and 34, and determines the polarity of the surface potential.

The phase of the AC output of the vibration 8 capacitor is the piezoelectric tuning fork 21.
With respect to the phase of the drive input of By comparing the phases of , the polarity of the surface potential can be determined.

FIG. 2 is a diagram showing an example of a specific electric circuit of the surface potential detection device shown in FIG. 1. Here, the detection electrode 23 that constitutes the photographic capacitor 23A is connected to the gate of a field effect transistor 41 that constitutes an impedance conversion circuit.

Field effect transistor 41 reduces the rather high output impedance of sensing electrode 23. The source output of the field effect transistor 41 is connected to the coupling capacitor 4
2 to an AC amplifier circuit 25 including an operational amplifier 43. This AC amplifier circuit 25 is configured similarly to the AC amplifier circuit 4 in the conventional surface potential detection device shown in FIG.

The output of the operational amplifier 43 that constitutes the AC amplifier circuit 25 is
The signal is applied to a rectifier circuit composed of an operational amplifier 44, diodes 45, 46, etc., converted into a DC signal, and an operational amplifier 46 forming an output circuit outputs a DC potential signal corresponding to the absolute value of the surface potential. What has been described so far is the configuration of the conventional surface potential detection device shown in FIG. 9 and that of Hayashi.

In this example, the output of the operational amplifier 43 constituting the AC amplifier circuit 25 is
The AC signal derived from No. 3 is also given to the phase shift circuit. The phase shift circuit 32 includes a differentiating circuit and a comparator 47, and shifts the phase of the applied alternating current signal. The output of the comparator 47 is further provided to a waveform shaping circuit. The waveform shaping circuit is
Resistor 48, Zener diode 49 and buffer rrc50
The signal that has passed through the Zener diode is used as a buffer for impedance adjustment and waveform shaping. TC50
The output of the buffer IC 50 is applied to one input terminal of an AND gate 51 constituting a logic circuit.

On the other hand, the output signal of the operational amplifier 53 forming the oscillation circuit of the piezoelectric tuning fork 21 is given to the other waveform shaping circuit. This waveform shaping circuit consists of a resistor 54, a Zener diode 55, and a buffer IC56. The signal that has passed through the Zener diode 55 is given to a buffer rrc56 for impedance adjustment and waveform shaping, and the output of the buffer IC56 is sent to a logic circuit. It is applied to the other input terminal of the AND gate 51.

Next, the operation will be explained. The output signal of the detection electrode 23 is impedance-converted by an impedance conversion circuit,
Further, the signal is amplified in an operational amplifier 43 that constitutes an AC amplifier circuit. The waveform of the output signal of this operational amplifier 43 is
Taking the case where the surface potential is +100 OV or -1000 V as an example, if the surface potential is positive, the result will be as shown in FIG. 3(a), and if it is negative, the result will be as shown in FIG. 3(b). That is, the output waveform of the AC amplifier circuit 25 is reversed depending on the polarity of the surface potential.

On the other hand, the output of the operational amplifier 43 is taken out as a DC potential signal according to the absolute value of the surface potential via a rectifier circuit and an output circuit 26. This is similar to the case of conventional surface potential detection devices.

On the other hand, since the output waveform of the operational amplifier 43 swings to both positive and negative polarities as shown in FIG.
The phase of the signal is shifted by a phase shift circuit consisting of a resistor 48 and a waveform shaping circuit consisting of a Zener diode 49. Therefore, and gate 5
The signal waveform input to one input terminal of 1 is as shown in FIG. 5(a) when the surface potential is positive, and as shown in FIG. 5(b) when the surface potential is negative.

On the other hand, the output waveform of the tuning fork oscillation circuit 27 used to excite the piezoelectric tuning fork 21 is as shown in FIG. A signal having a waveform shown in FIG. 6 is input to the other input terminal of the AND gate 51.

Therefore, when the surface potential is positive, the AND gate 51 outputs the logic signal shown in FIG. 7(a), and conversely, when the surface potential is negative, the logic signal shown in FIG. 7(b) is output. is obtained.

In the above embodiment, a piezoelectric tuning fork is used as the piezoelectric vibrator, but it goes without saying that piezoelectric vibrators of other shapes can also be used.

[Effects of the Invention] The present invention provides a polarity determining means that compares the phase of the output signal from the detection electrode with the phase of the output signal of the oscillation circuit used to drive the piezoelectric vibrator to determine the polarity of the surface potential. , it is possible to measure not only the absolute value of the potential on the surface of the object to be measured, but also the polarity.

Therefore, it is possible to realize a surface potential detection device that can supply more airx information.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an embodiment of the present invention, and FIG.
The figure is a diagram showing an example of a specific electric circuit of the embodiment shown in FIG. 1. Figure 3 is a diagram showing the output waveform of the AC amplifier circuit. Figure 3 (a) shows when the surface potential is positive, (b
) is negative. FIG. 4 is a diagram showing the output waveform of the piezoelectric tuning fork oscillation circuit. Figure 5 is a diagram that does not show the output waveform after passing through the phase shift circuit and waveform shaping circuit, and Figure 5 (a) shows the case where the surface potential is positive, and Figure 5 (b) shows the case where the surface potential is square. shows. FIG. 6 is a diagram showing the output waveform of the 7M tuning fork oscillator circuit that has passed through the waveform shaping circuit. FIG. 7 is a diagram showing the output waveform of the polarity determining means, where FIG. 7(a) shows the case where the surface potential is positive, and FIG. 7(b) shows the case where the surface potential is negative. FIGS. 8 and 9 are a schematic block diagram and a specific electric circuit diagram showing an example of a conventional surface potential detection device. In the figure, 21 is a piezoelectric vibrator, and the pressure of C is ff1l or
23 is a detection N pole, 24 is a surface potential detection signal processing section, 27
3 is an oscillation circuit, 31 is a polarity determining means, 32 is a phase shift circuit, and 3
3.34 is a waveform shaping circuit, and 35 is a logic circuit.

Claims (2)

[Claims] (1) A piezoelectric vibrator, an oscillation circuit for driving the piezoelectric vibrator, a detection electrode attached to the piezoelectric vibrator, and a signal that processes the output signal from the detection electrode and generates a signal according to the potential of the surface of the measurement target. and a surface potential detection signal processing unit that outputs the
The oscillatory capacitive surface potential detection device further includes polarity determining means for comparing the phase of the output signal from the detection electrode and the phase of the output signal of the oscillation circuit to determine the polarity of the potential on the surface of the measurement target. A surface potential detection device characterized by: (2) The polarity determining means includes a phase shift circuit that shifts the phase of an output signal derived from the detection signal, and a logic circuit that compares the output signal of the phase shift circuit with the phase of the output signal of the oscillation circuit. , a surface potential detection device according to claim 1.