JPH07218567A - Vibration-free a.c. non-contact surface potential measuring electrometer - Google Patents

Abstract

PURPOSE:To manufacture an AC non-contact type surface potential measuring electrometer by manufacturing probes by which the surface potential of an object plane to be measured can be measured without using mechanical vibration. CONSTITUTION:Regarding a probe which is manufactured by installing and fixing a reference electrode 17 and a detection electrode 18 in a conductive case 1; wherein the case 1 has a through detection hole 2 on the opposite to an object to be measured 40; the electrode 17 detects electric fluxes lines from the object to be measured 40; and the electrode 18 is set behind the electrode 17 and capacity coupled with the electrode the reference electrode 17 is switched to the case 1 and the detection electrodes 18 continuously and reciprocally, so that a.c. voltage proportional to the surface potential of the object to be measured 40 can be detected and displayed as the surface potential on an electrometer or an ammeter through an amplifier 35 and a signal processing circuit for a synchronous detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to non-contact measurement of the surface potential of a substance, and relates to the measurement of the potential such as static electricity.

[0002]

2. Description of the Related Art Conventional surface potential measurement is classified into a static type and an alternating type. The operating principle of static surface potential measurement is shown in FIG. When the detection electrode 8 is brought close to the charged substance 40, a voltage is induced by electrostatic induction. However, the induced voltage is discharged by the time constants 3 and 4 of the detection electrode. Therefore, when the measured voltage is direct current, the surface potential cannot be continuously measured. In contrast to this method, in the case of the AC type, the voltage generated at the detection electrode by changing the electric coupling between the detection electrode and the object to be measured or the electric field strength received by the detection electrode becomes the surface potential of the object to be measured. It can be obtained as a proportional AC voltage. A vibrator or a speaker is used as a means for changing the coupling between the detection electrode and the object to be measured. These are those that vibrate mechanically.

As an example, the operation principle of a sector type using a tuning fork is shown in FIGS. This is a conductive case 1 having a detection hole 2 through which the electric force line radiated from the object to be measured is incident, a chopper section 7 for cutting the electric force line coming into the case 1, and this electric force. A tuning fork 10 to which a piezoelectric ceramic 9 for driving is adhered is used for the chopper portion 7, and the chopper portion at the tip of the tuning fork 10 is used. The line of electric force is cut at 7. The detection electrode 8 is fixed to the substrate 11, and the chopper portion 7 and the substrate 11 are housed in the case 1 having the detection hole 2. Further, the driving terminal 12, the output terminal 13, and the ground terminal 14 of the tuning fork 10 are attached to the substrate 11, and the driving terminal 12 and the piezoelectric ceramic 9 are attached.
Wiring 15 is provided between the and.

Next, FIGS. 4 and 5 show the operating principle of the vibration capacitance type using a tuning fork. This is a conductive case 1 having a detection hole 2 through which the lines of electric force emitted from the object to be measured are incident, a vibrator for changing the coupling capacitance with the object to be measured, and the lines of electric force. The tuning fork 10 is composed of a detection electrode 8 for receiving the AC signal in response to the received signal, and the vibrator uses a tuning fork 10 to which a driving piezoelectric ceramic 9 is adhered. The tip of the tuning fork 10 faces the detection hole. The detection electrode 8 is fixed at the position, and the vibrator and the substrate 11 are housed in the case 1 having the detection hole 2. Further, a drive terminal 12, an output terminal 13, and a ground terminal 14 of the tuning fork 10 are attached to the substrate 11, a wiring 15 is provided between the drive terminal 12 and the piezoelectric ceramic 9, and the detection electrode and the output terminal 13 are connected. Wiring 16 is provided between the spaces.

[0005]

However, in such a conventional probe as described above, mechanical vibration is used to change the lines of electric force to obtain an AC signal. According to this, it is difficult to perform mechanical manufacturing work such as a work of adhering a detection electrode or the like in the case of a piezoelectric ceramic or a vibration capacitance type, or a work of accurately fixing the mounting of the tuning fork to the detection electrode, and thus it is difficult to achieve uniformity Since the error is large and individual differences occur in the AC signals that can be detected, individual adjustments were made in the processing circuit.

Further, since a tuning fork or the like is used, there are large structural restrictions.

An object of the present invention is to solve these problems by means of detecting electric lines of force and converting them into an AC signal by means not relying on mechanical vibration.

[0008]

The surface electrometer of the present invention comprises:
It has the following configuration. That is, the detection electrode is built in the conductive case, the detection hole is opened in the facing wall surface portion, the reference electrode is fixed between the detection hole and the detection electrode, and the reference electrode is electrically and continuously connected. A surface electrometer comprising a probe provided with a circuit alternately connected to a case and a detection electrode, and an AC signal processing circuit.

[0009]

The operation of the present invention will be described with reference to the drawings. FIG. 6 is a diagram showing the principle of operation of a surface electrometer comprising a probe and a signal processing circuit according to the present invention. The line of electric force from the DUT 40 to the detection hole 2 of the probe reaches the reference electrode 17. Here, when the switch 20 which connects the reference electrode 17 to the detection electrode and the conductive case alternately and continuously is operated, an AC signal proportional to the surface potential of the DUT 40 is obtained at the detection electrode. To be The AC signal passes through the impedance conversion circuit 24, is amplified by an amplifier circuit 35 to a required voltage, is detected by a synchronous detection circuit 36, and is smoothed by a smoothing circuit 38.
After being converted to direct current by, the surface potential of the object to be measured can be measured by displaying it on the display circuit 39. The oscillator circuit 37 is a signal generation circuit for driving the switch 20.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 7 is a top view of the probe A according to the present invention.
Further, FIG. 8 is a cross-sectional view of the probe A seen from the side surface. FIG. 9 is an equivalent diagram of the probe A. Reference numeral 1 denotes a conductive case, which is made of metal. This case 1
The shape of is not limited to the illustrated one, and may be, for example, an elongated shape or a cylindrical shape. Reference numeral 2 denotes a detection hole, which is provided on the counter wall surface portion inside the conductive case 1 and is for detecting static electricity. Reference numeral 17 is a reference electrode, which detects a line of electric force entering from the detection hole. Reference numeral 18 denotes a detection electrode, which detects the ground potential by electrostatic induction when the switching circuit 20 connects the reference electrode 17 to the conductive case 1 having the ground potential,
When the switching circuit 20 connects the reference electrode 17 to the detection electrode 18, the line of electric force from the DUT 40 is detected. Reference numeral 19 is made of an insulating material, and is provided to fix the reference electrode 17 and the detection electrode 18. 20 is a reference electrode 1
This is a switching circuit in which 7 is common, and the detection electrodes 18 and the conductive case 1 are sequentially and alternately connected. Two
Reference numeral 4 is a circuit having a high input impedance and a low output impedance. Reference numeral 21 is a terminal for taking out the detected AC signal. 22 is an electric signal for continuously operating the switching circuit. Reference numeral 23 is a terminal connected to the conductive case.

FIG. 10 and FIG. 11 are an equivalent circuit of an experimental device for demonstrating that the probe by this mechanism can detect the surface potential and convert it into alternating current. This experiment is used to measure the potential distribution of electric lines of force in static electricity. Two
Reference numeral 5 is an insulating water tank storing water, 26 is an electrode plate corresponding to the conductive case of the probe, 27 is an electrode plate corresponding to the reference electrode, and 28 is an electrode plate corresponding to the detection electrode. Yes, 29 is an electrode plate assuming the object to be measured.
Reference numeral 30 is a resistor corresponding to the resistance of the detection electrode, and the changeover switch 32 is manually wired so that the reference electrode is connected to the detection electrode or the conductive case. 31 is a voltmeter with an extremely high input impedance, which measures the potential of the detection electrode. A voltage generator 33 applies a potential equivalent to the potential of the measured object. In the experiment using this water tank, it was possible to measure the potential distribution of the electric force lines of static electricity as the equipotential lines of the potential, but it was confirmed that the measurement value of the voltmeter 31 changes by simply switching the switch 32. FIG. 12 shows the measurement result of this experiment.

FIG. 13 shows an actual circuit. Reference numeral 41 is a high input impedance FET, which is a source follower circuit. Reference numerals 34 and 42 denote FET bias circuits which stabilize the operation of the FET. Reference numeral 46 is an operational amplifier, the amplification factor of which is determined by the resistors 44 and 45, and amplifies the detected AC signal. The capacitor 43 is inserted to transmit only the AC signal detected by the probe, and eliminates the DC component. The resistor 47 and the FET 48 are a synchronous detection circuit,
The operational amplifier 56 is a buffer circuit. The resistor 57 and the capacitor 58 are an integrating circuit and smooth the pulsating current signal after performing the synchronous detection. The operational amplifier 59 is a buffer circuit. 61 is a square wave oscillator. The FET switch circuits 54 and 55 are optically coupled, and the LE on the drive side is
It has a function of turning on the FET when a current is passed through D, and turning off the FET when the current of the LED is stopped. Use this function,
By alternately passing a current through the LED, the reference electrode can be connected to the detection electrode and the case alternately. Reference numeral 51 is an inverting logic circuit which alternately controls the FET switch circuits 54 and 55.

In this circuit, the polarity of the detected AC signal is detected by performing synchronous detection on the phase of the AC signal. However, if it is not necessary to display the polarity, it is possible to simply perform rectification and display the voltage.

Further, the feedback voltage becomes equal to the potential of the object to be measured by feeding back the voltage to the detection electrode and configuring the circuit so that the detection voltage always shows zero potential. Therefore, the surface potential of the object to be measured can be measured by measuring and displaying this feedback voltage. In this case, if the amount of feedback is sufficiently large, a surface electrometer that does not depend on the distance between the object to be measured and the probe can be manufactured.

[0015]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, when measuring the surface potential of an object to be measured, the surface potential can be measured in a non-contact manner without using mechanical vibration, so that the productivity of the probe is high. Also, since the shape can be freely manufactured, it is possible to manufacture a product having a shape and a size suitable for the purpose. Moreover, since no mechanical vibration is used, there is an effect that a highly reliable product can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing the operating principle of a static surface electrometer.

FIG. 2 is a cross-sectional view of a conventional sector probe.

FIG. 3 is a vertical cross-sectional view of a conventional sector probe.

FIG. 4 is a cross-sectional view of a conventional vibration capacitance type probe.

FIG. 5 is a vertical cross-sectional view of a conventional vibration capacitance type probe.

FIG. 6 is a diagram showing the principle of operation of the surface electrometer according to the present invention.

FIG. 7 is a top view of probe A according to the present invention.

FIG. 8 is a sectional view of a probe A according to the present invention as seen from a side surface.

FIG. 9 is an equivalent circuit diagram of the probe A according to the present invention.

FIG. 10 is a diagram showing a device for measuring equipotential lines in a water tank for demonstrating that the probe according to the present invention can measure the surface potential of a measured object.

FIG. 11 is an equivalent circuit diagram of a device for measuring equipotential lines in a water tank for demonstrating that the probe according to the present invention can measure the surface potential of a measured object.

FIG. 12 is an experimental result by an equipotential line measuring device using a water tank for demonstrating that the probe according to the present invention can measure the surface potential of a measured object.

FIG. 13 shows an actual circuit example of a surface electrometer using probe A.

[Explanation of symbols]

 1 Conductive Case 2 Detection Hole 3 Input Resistance 4 Input Capacitance 5 FET 6 Bias Resistor 7 Chopper 8 Detection Electrode 9 Piezoelectric Ceramic 10 Tuning Fork 11 Board 12 Drive Terminal 13 Output Terminal 14 Ground Terminal 15 Wiring 16 Wiring 17 Reference Electrode 18 Detection Electrode 19 Insulation material 20 Switching circuit 21 Output terminal 22 Driving terminal 23 Grounding terminal 24 Impedance conversion circuit 25 Water tank containing water 26 Electrode plate equivalent to conductive case 27 Electrode plate equivalent to reference electrode 29 Electrode plate equivalent to object to be measured 30 Resistor equivalent to input resistance 31 Voltmeter 32 Switching circuit 33 Voltage generator 34 Input resistance 35 Amplifier 36 Synchronous detection circuit 37 Signal generation circuit 38 Smoothing circuit 39 Display circuit 40 Measured object 41 FET 42 Resistor 43 Capacitor 44 Resistor 45 Resistor 46 Operational Amplifier 47 Resistor 48 FET 49 Protection diode 50 Resistor 51 Logic inverting circuit 52 Current limiting resistor 53 Current limiting resistor 54 LED-FET photocoupler 55 LED-FET photocoupler 56 Operational amplifier 57 Smoothing resistor 58 Smoothing capacitor 59 Operational amplifier 60 Voltmeter 61 Oscillator 62 Capacitor for preventing abnormal oscillation 63 Capacitor for determining oscillation frequency 64 Resistor for determining oscillation frequency 65 Resistor for determining oscillation frequency

Claims (1)

[Claims] 1. A reference electrode is fixed on the front surface of a detection electrode to be capacitively coupled, and the reference electrode is cycled in a surface potential probe configured so that the lines of electric force from the opposite measured surface reach the reference electrode. A non-contact surface electrometer that measures the surface potential of the surface to be measured by alternating the electric lines of force input to the surface potential probe by providing a switching circuit that connects the detection electrode and the ground potential alternately alternately. .