JPS5847672B2 - surface electrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface electrometer that uses a vibrator instead of a vibrating electrode when detecting the surface potential of a charged object by capacitance division.

A surface electrometer measures the surface potential of a charged object by placing a detection electrode in front of a charged object and reading the potential induced in the detection electrode.

The potential induced in the sensing electrode is proportional to the electric field near the sensing electrode.

Since this electric field is proportional to the surface potential of the charged object, the surface potential can be determined from the measurement of the electric field.

An example of the configuration of a conventional surface electrometer is shown in FIG.

1 is the charged object, 2 is the detection electrode, 3 is the indicator, Ca is the capacitance between the charged object 1 and the detection electrode 2, and cb is the detection electrode 2
is the capacitance between

The surface potential of the charged object 1 is VS, and the potential of the detection electrode 2 is ■d
Then, the following formula holds true.

In the conventional example shown in FIG. 1, the surface potential Vs is measured by capacitance division, as is clear from equation (1).

One of the measurements using this capacitance division uses a vibrating electrode.

This vibrates the detection electrode 2 so as to bring it closer to or away from the charged object 1, increases or decreases the amount of charge induced in the detection electrode 2 in synchronization with the vibration, and extracts it as an alternating current signal.

Measurement using a vibrating electrode has the advantage of obtaining high-resolution measured values, but requires a mechanism for vibrating the detection electrode 2, resulting in a problem that the structure is complex and expensive.

This invention is intended to solve this problem, and by fixing the detection electrode 2 and vibrating a vibrator installed near the detection electrode 2, a simple and inexpensive electrometer can be created. This is what we provide.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

First, a configuration diagram of an embodiment according to the present invention is shown in FIG.

4 is a vibrator, and the vibrator 4 is constructed with a conductor and is grounded.

In the figure, a tuning fork is used as the vibrator 4.

4a and 4b are vibrating pieces of the vibrator 4, and the vibrating pieces 4a and 4 are arranged so as to sandwich the side surface of the detection electrode 2 facing the charged object 1.
b to face each other.

Although FIG. 2 shows a cylindrical detection electrode 2, it may also have a prismatic shape.

Next, the metadiagram of Figure 2 is shown in Figure 3.

The vibrating pieces 4a and 4b are arranged parallel to the line connecting the charged object 1 and the detection electrode 2, respectively.

In FIGS. 2 and 3, the vibrating pieces 4a and 4b of the vibrator 4 are vibrated by moving them closer to or away from the sensing electrode 2, without vibrating the sensing electrode 2.

When the vibrating pieces 4a and 4b are vibrated, the capacitance C1 between the charged object 1 and the detection electrode 2 increases and decreases, and at the same time, the capacitances C2 and C3 between the detection electrode 2 and the vibrating pieces 4a and 4b also increase and decrease. .

Then, an AC signal proportional to the surface collapse potential Vs of the charged object 1 is obtained at the detection electrode 2.

Now, if the minimum value of capacitance C1 is C1min, then capacitance C
1mjn is obtained when the vibrating pieces 4a, 4b are brought closer to the detection electrode 2.

This is because when the vibrating pieces 4a and 4b approach the detection electrode 2, the lines of electric force from the charged object 1 to the detection electrode 2 reach the vibrating pieces 4a and 4b at the ground potential, and the number of lines of electric force reaching the detection electrode 2 decreases. It is from.

The capacitances C2 and C3 when the vibrating pieces 4a and 4b approach the detection electrode 2 are respectively C 2 rna X ,
If C3max is assumed, and ΔC is the change in capacitance when the vibrating pieces 4a and 4b are separated from the detection electrode 2 with respect to the capacitances C2maX and C3max, the following equation is obtained.

Furthermore, if the change in capacitance C1 when the vibrating pieces 4a and 4b move away from the detection electrode 2 is ΔC1, then the following equation (
4) is obtained.

Since Figures 2 and 3 are also surface electrometers based on capacitance division, the following equation (5) holds true in the same way as equation (1). Capacity C1
is very small compared to capacitances C2 and C3, so equation (5)
can be expressed by the following equation (6).

Since the capacitance c1min when the vibrating pieces 4a and 4b approach the detection electrode 2 is sufficiently smaller than the capacitance ΔC1, equation (6) can be further expressed by the following equation (7).

From equation (7), the periodic variation ΔVd caused by the vibration of the vibrating pieces 4a and 4b is as follows.

This amount of change ΔVd is an alternating current signal and is proportional to the surface potential Vs of the charged object 1.

Therefore, if the amount of change ΔVd is amplified by the amplifier 5, a measurement value with high resolution can be obtained.

Note that when the vibrators 4a and 4b are brought close to the charged object 1 as shown in FIG. 2, capacitances C4 and C5 are added between the charged object 1 and the vibrators 4a and 4b, The rise in the true value of the measured value of the surface potential Vs also becomes lower.

Therefore, it is necessary to make the capacitances C4 and C5 as small as possible.

In the embodiments of FIGS. 2 and 3, capacitance C4. The vibrators 4a and 4b are arranged parallel to the line connecting the charged object 1 and the detection electrode so that C5 becomes as small as possible.

Here, an actual measurement example according to the present invention will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a schematic diagram showing the dimensions of each part of an actual measurement example.

In the figure, the outer diameter of the detection electrode 2 is Q. 5 mm, vibrating piece 4a
, 4b by 3 degrees, and the distance T between the vibrating pieces 4a and 4b.
2, and the distance between the charged object 1 and the tips of the vibrating pieces 4a and 4b is rubbed by 5 mml each.

In this state, the line connecting the tips of the vibrating pieces 4a and 4b is taken as a reference line, the distance where the detection electrode 2 is closer to the charged object 1 than the reference line is +L, and the distance where the detection electrode 2 is on the opposite side of the charged object 1 from the reference line is +L. Let be -L.

FIG. 5 is a diagram showing the relationship between detection sensitivity S and distance L when measured under these conditions.

According to FIG. 5, when the distance L is about -0.5 degrees, in other words, when the detection electrode 2 is slightly inserted between the vibrating pieces 4a and 4b, the detection sensitivity S is at its maximum.

This indicates the position of the detection electrode 2 for efficient conversion when converting the surface potential into an alternating current signal.

As explained in detail above, according to the present invention, surface potential can be measured using an inexpensive vibrator such as a tuning fork, and since there is little measurement error, it is possible to create a detection part with good performance. I can do it.

Furthermore, since the structure is simple, it is possible to provide one that operates stably over a long period of time.

[Brief Description of the Drawings] Fig. 1 shows an example of the structure of a conventional surface electrometer, Fig. 2 shows a structure of an embodiment according to the present invention, Fig. 3 is a top view of Fig. 2, and Fig. 4 shows an example of the structure of a conventional surface electrometer.
FIG. 5 is an explanatory diagram of an actual measurement example according to the present invention. 1...Charged object, 2...Detection electrode, 3
...Indicator, 4...Vibrator, 4a,
4b... Vibration piece, 5... Amplifier, C
1...Capacitance between charged object 1 and detection electrode 2, C2...Capacitance between detection electrode 2 and vibrating piece 4a, C3...Detection Capacitance between electrode 2 and vibrating piece 4b, C4... Capacitance between vibrating piece 4a and charged object 1, C5... Between vibrating piece 4b and charged object 1 capacitance.

Claims (1)

[Claims] 1. In a surface electrometer that detects the surface potential of a charged object by capacitance division, a first vibrating piece and a second vibrating piece of a vibrator are made to face each other so as to sandwich the side surface of a detection electrode facing the charged object, and The first vibrating piece and the second vibrating piece are arranged parallel to a line connecting the charged object and the detection electrode, respectively, and the first vibrating piece and the second vibrating piece are moved closer to or away from the detection electrode. 1. A surface electrometer that measures the surface potential of the charged object by vibrating the charged object.