JP2555956B2 - Potential sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a potential sensor for detecting the surface potential of a charged body, and more particularly to a potential sensor having a function of converting an AC signal by a mechanical oscillator.

[0002]

2. Description of the Related Art As shown in FIGS. 3 (a) and 3 (b), a conventional electric potential sensor has a measurement hole 119 opened to introduce an electric force line 118 emitted from an object to be measured. A case 115 having the same, a tuning fork vibrator 121 having a chopper portion 123 for cutting the electric force line 118 coming into the case 115 at a constant cycle, and a detection for receiving the cut electric force line 118 and extracting an AC signal. It is composed of an electrode 112.

A piezoelectric ceramic 117 for driving and extracting a vibration signal is bonded to the tuning fork vibrator 121. Further, the tuning fork vibrator 121 and the detection electrode 112 are arranged on the substrate 11
6 and the substrate 116 is fixed to the case 11
It is housed in 5. An input / output terminal 162 extending outside the substrate 116 is connected to the piezoelectric ceramic 117 via a piezoelectric ceramic wiring 132.
A ground terminal 172 is connected to the tuning fork vibrator 121. An output terminal 152 extending outside the substrate 116 is connected to the detection electrode 112.

In the above-mentioned potential sensor, since the voltage signal is applied to the piezoelectric ceramic 117 for driving and signal extraction, this signal is passed through the space inside the sensor to the detection electrode 1.
Induction noise is given to 12. The detection electrode 112 is kept at a high impedance in order to amplify a minute signal, and is susceptible to noise from the piezoelectric ceramic 117. If this noise has no lines of electric force, that is, the charging potential of the measured object is 0
Even when it is V (volt), it is detected as an AC output to some extent and becomes an offset output.

Therefore, the conventional potential sensor has a drawback that the offset output causes a measurement error in the output of the potential sensor and the measurement of the charged potential of the object to be measured becomes inaccurate. To overcome this, a potential sensor as shown in FIG. 4 is proposed in Japanese Patent Laid-Open No. 3-100474 in order to cancel the offset output by using the drive signal of the tuning fork vibrator 121. As this potential sensor, the same reference numerals are given to the same members by using the potential sensors of FIGS. 3A and 3B, and a part of the description is omitted.

This potential sensor has a chopper section 1 for intermittently interrupting a line of electric force radiated from an object to be measured at regular intervals.
23, the detection electrode 112 that receives the electric lines of force 118 that have passed through the chopper portion 123, the preamplifier 211 that amplifies the signal from the detection electrode 112, and the substrate 116 on which the chopper portion 123, the detection electrode 112, and the preamplifier 211 are mounted.
And a measurement hole 119 for introducing the electric force line 119.

Further, the potential sensor includes a case 115,
The tuning fork drive circuit 212 that drives the chopper unit 123, the attenuator 213 that attenuates the drive signal, the variable amplification circuit 214 that changes the amplitude and phase of the signal from the attenuator 213, the signal from the preamplifier 211, and the variable amplification circuit 214. Adder circuit 215 for adding the signal from
And have.

Chopper portion 12 at the tip of tuning fork vibrator 121
3, the lines of electric force 119 are cut at a predetermined cycle. The tuning fork vibrator 121 is excited by the tuning fork driving circuit 212,
It vibrates with a natural period. At this time, the piezoelectric ceramics 11
Due to the voltage and current applied to 7, noise equal to the driving frequency is generated on the detection electrode. This signal is the preamplifier 211
Is amplified and converted by impedance, and the waveform is converted into a sine wave by the filter 216.

On the other hand, the drive signal of the tuning fork vibrator 121 is attenuated by the attenuator 213, the amplitude and phase are adjusted by the variable amplifier circuit 214, and the adder circuit 215 is added.
Sent to At this time, the output signal B from the filter 216 and the output signal D from the variable amplifier circuit 214 have a phase difference of 180 degrees and different amplitudes so that the amplitudes are equal.
The output from the adder circuit 215 is adjusted to 0V by adjusting with 17.

[0010]

In the potential sensor proposed above, the fact that the drive signal of the tuning fork vibrator 121 has the same frequency as the offset output and is a constant voltage, and the offset output and the phase are 180 degrees, By creating signals with different amplitudes and adding them to the output of the potential sensor,
It is intended to cancel the offset output.

However, since the adder circuit 215 for adding the signal for canceling the offset is required, the signal processing circuit becomes complicated.

Therefore, an object of the present invention is to provide a potential sensor capable of canceling an offset output with a simple structure.

[0013]

According to the present invention, a case having a measurement hole for introducing the electric force line radiated from an object to be measured, and the electric force line entering the case are received. In a potential sensor including a bending oscillator having a detection electrode, a wiring substrate holding the bending oscillator, and a base holding the wiring substrate, a DC voltage is present behind the detection electrode when viewed from the measurement hole. A potential sensor is obtained which is provided with an auxiliary electrode to be applied .

Further, according to the present invention, the bending oscillator includes a first metal plate which is the detection electrode and a second metal plate.
When an insulating plate connected to each other so as to be arranged the first and second metal plates on one plane, for driving and vibration signal extraction of the bent vibrator to the second metal plate on adhered to
And at least two piezoelectric ceramics were, the first
1 metal plate is held on the wiring board via the first supporting portion
And the second metal plate is connected via the second support portion.
A potential sensor is obtained which is held on the wiring board .

[0015]

According to the present invention, the detection electrode, which is the first metal plate that receives the lines of electric force, the second metal plate, and the insulating plate for connecting these so as to be arranged on one surface are provided. The bending oscillator including it is vibrated in the same direction as the line of electric force.
A potential sensor without offset output is realized by applying a predetermined DC voltage to an auxiliary electrode provided behind the detection electrode section.

[0016]

EXAMPLE Next, the potential sensor of the present invention is shown in FIG.
A description will be given based on (a), FIG. 1 (b) and FIG.

Referring to FIGS. 1A and 1B, the potential sensor includes a detection electrode 2 which is a first metal plate, and a bending vibration which is the detection electrode 2 and the second metal plate 20. Insulation plate 3 in which child 1, detection electrode 2 and bending oscillator 1 are connected to each other
A wiring board 4 holding the bending oscillator 1 and the detection electrode 2 via the first support 9 and the second support 10, an auxiliary electrode 22 provided behind the detection electrode 2, and a wiring board. It has a base 6 holding 4 and a case 5.

The auxiliary electrode 22 is provided on the wiring board 4 and faces the detection electrode 2. The detection electrode 2, the bending oscillator 1, the auxiliary electrode 22, and the wiring board 4 are the base 6
It is housed inside surrounded by a case 5. The case 5 is formed with a measurement hole 19 for introducing the electric force line 18 radiated from the object to be measured into the detection electrode 2.

The bending oscillator 1 is integrated with the detection electrode 2 which receives the electric force lines 18 coming into the case 5.
The auxiliary electrode 22 is located behind the detection electrode portion 2 when viewed from the measurement hole 19. The detection electrode 2 and the second metal plate 20 are connected by the insulating plate 3 so that the bending oscillator 1 is arranged on one plane. On the second metal plate 20, at least two piezoelectric ceramics 7 bonded for driving the bending oscillator 1 and extracting a vibration signal are provided.

A cable 8 is drawn in the inside surrounded by the base 6 and the case 5, and the output wiring 11 and the ground wirings 12 and 14 of the cable 8 are used as a conductive pattern of the wiring board 4. It is connected. The piezoelectric ceramic wiring 13 is connected to the conductive pattern of the wiring board 4.

Next, the operation of the potential sensor will be described with reference to FIG. The two piezoelectric ceramics 7 for driving and extracting vibration signals, which are bonded to the bending oscillator 1, are connected to the driving circuit 25. Therefore, the bending oscillator 1 is bent and vibrated by the drive circuit 25. This vibration causes the detection electrode 2 to vibrate up and down as shown by an arrow A in FIG. 1B, so that the potential generated in the detection electrode 2 also periodically changes.

Therefore, between the detection electrode 2 and the ground,
An AC signal having the same frequency as the vibration of the bending oscillator 1 and having a magnitude corresponding to the amplitude is generated. This AC signal is connected to the wiring on the wiring board 4 via the first support portion 9 connected to the detection electrode portion 2. Further, the voltage of this AC signal is so small that it is amplified by the preamplifier 26 having a high input impedance and output from the preamplifier 26 in order to be converted into a signal that can be easily handled.

Next, when a DC voltage V is applied to the auxiliary electrode 22 located behind the detection electrode 2, the detection electrode 2 is
When the polarity of this DC voltage V is the same as the polarity of the charging voltage of the object to be measured, the same AC signal having a frequency that is 180 degrees out of phase with the AC signal generated by the object to be measured is generated. On the contrary, when the voltage applied to the auxiliary electrode 22 and the charging voltage of the object to be measured have different polarities (one is positive and the other is negative), the phases of the AC signals generated at the detection electrodes 2 by the respective voltages match.

On the other hand, the offset output generated as noise has the same frequency as the AC signal generated in the detection electrode 2, and the phase difference is 0 degree or 180 degrees. For this reason,
By adjusting the polarity and the magnitude of the voltage V applied to the auxiliary electrode 22, it is possible to generate the same AC signal having a phase different from the offset output by 180 degrees and cancel the offset voltage.

Therefore, a potential sensor having no offset output can be realized. Further, the variable resistor 27 and the preamplifier 26 can be provided on the wiring board 4 in the potential sensor.

[0026]

As described above, according to the present invention, by adding a simple circuit for applying a DC voltage to the auxiliary electrode, an electric potential sensor having no offset output, a simple structure, and accurate measurement can be obtained.

[Brief description of drawings]

FIG. 1 shows an embodiment of a potential sensor of the present invention, (a)
Is a plan sectional view, and (b) is a front sectional view.

FIG. 2 is a block diagram showing the operation of the potential sensor of the present invention.

3A and 3B show an example of a conventional potential sensor, FIG. 3A is a plan sectional view, and FIG. 3B is a front sectional view.

FIG. 4 is a block diagram showing another example of a conventional potential sensor.

[Explanation of symbols]

 1 Bending Oscillator 2,112 Detection Electrode 3 Insulation Plate 4 Wiring Board 5,115 Case 6 Base 7,117 Piezoelectric Ceramic 18,118 Electric Force Line 19,119 Measuring Hole 20 Second Metal Plate 22 Auxiliary Electrode 23,123 Chopper Part 25 Drive circuit 26 Preamplifier 27 Variable resistor 121 Tuning fork vibrator 212 Tuning fork drive circuit 213 Attenuator 214 Variable amplification circuit 215 Adder circuit

Claims (2)

(57) [Claims] 1. A case having a measuring hole for introducing a line of electric force radiated from an object to be measured, a bending vibrator having a detection electrode for receiving the line of electric force entering the case, and In a potential sensor including a wiring board holding a bending oscillator and a base holding the wiring board, a DC voltage is applied behind the detection electrode when viewed from the measurement hole.
An electric potential sensor characterized in that an auxiliary electrode is provided. 2. The bending oscillator is the detection electrode.
A first metal plate, a second metal plate, an insulating plate connected to each other so as to be disposed in the first and second metal plates on one plane, the said second metal plate on and at least two piezoelectric ceramic adhered to the driving and vibration signal extraction of the bending transducer, the support the first metal plate first
Is held on the wiring board via a section, and
The metal plate is held on the wiring board via the second supporting portion.
The potential sensor according to claim 1, wherein the are.