JPH04305171A - Method and apparatus for measuring surface charge density - Google Patents

Abstract

PURPOSE:To simultaneously measure the charges on both surfaces of a charge body within a real time even during movement by opposing two detection electrodes to each other so as to hold the charge body between both electrodes. CONSTITUTION:Two first and second detection electrodes 1, 2 are respectively mounted on speakers 5, 6 to be opposed mutually so as to hold a charge body between both electrodes. Signals of frequencies different from each other are applied to the speakers 5,6 from oscillators to vibrate both electrodes 1, 2 in the direction vertical to the surface of charge body 3. As a result, the voltages corresponding to the surface charge densities on both surfaces of the charge body appear in the electrodes 1, 2. After these voltages are amplified by a voltage amplifier 9, only the vibration frequency components of said voltages are extracted by first and second band bypass filters 10, 11. The outputs of said filters are converted to digital values by A/D converters 12, 3 and charge densities are operated by a CPU 14 and the surface charge densities on both surfaces of the charge body 3 can be simultaneously calculated within a real time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface charge density measuring method and apparatus for simultaneously measuring charge densities on both surfaces of a charged body such as a film.

0002

2. Description of the Related Art Conventionally, a typical method for measuring the charge density on both surfaces of a charged body such as a film is a method using a distance-compensated electrometer as shown in FIG. In the figure, 20 is a probe unit incorporating a detection electrode 21 and a vibrating body 22, 23 is an oscillator, 24 is a preamplifier, 25 is an amplifier, 26 is a synchronous detector, 27 is an integrator,
28 is a high voltage generator, and 29 is an impedance matching circuit. When the detection electrode 21 is made to face the charged body 30 while being vibrated, an AC voltage corresponding to the electric field strength E2 is applied to the detection electrode 2.
1, a DC voltage Vb corresponding to this AC voltage is generated in the high voltage generator 28, and this Vb is fed back to the probe unit 20. This Vb acts in the direction of canceling E2, starts rising from 0, and becomes a constant value when E2=0. At this time, the following relationship 1 holds true.

0003

[Math 1]

[0004] Here, σ1* and σ2* are surface charge densities,
ε0 is the dielectric constant of air, ε is the dielectric constant of the charged body 30, h is the thickness of the charged body 30, and x1 is the distance between the charged body 30 and the ground electrode 31. To find σ1* and σ2*, first measure the Vb values Vb1 and Vb2 such that E2=0 for at least two different values of x1, x11 and x12, and then calculate the straight line equation that represents the Vb-x1 characteristic. seek. Then, the slope of this straight line is ΔVb/Δx1 and this straight line is x1=
From the value Vb0 when extrapolated to 0 and the equation of equation 1 above, the following relational equations of equations 2 and 3 are obtained, and from these equations, σ1
* and σ2* are found.

[0005]

[Math 2]

[0006]

[Math 3]

[0007]

[Problem to be Solved by the Invention] However, the method using such a distance-compensated electrometer is not superior to other conventional methods when it comes to measuring the potential itself because it can measure the potential itself instantaneously. However, in order to determine the charge density on both sides of the charged body, the distance between the detection electrode and the charged body must be changed at least twice as described above to determine the potential, so this cannot be done instantly. Therefore, it is not suitable for measurement when a charged body is moving. Further, since the distance compensation electrometer incorporates a feedback mechanism including a high voltage generator, it is dangerous, requires careful handling, and is expensive.

The object of the present invention is to measure the surface charge density on both surfaces of a charged body simultaneously and in real time, even during movement, and in an essentially non-hazardous and economical manner. An object of the present invention is to provide a method for measuring and a device for the same.

[0009]

[Means for Solving the Problems] In the measurement method according to the present invention, two detection electrodes are made to face each other with a charged body in between and are vibrated perpendicularly to the surface of the charged body at different frequencies, and the outputs of these detection electrodes are Measure through a filter corresponding to that vibration frequency.

The measuring device according to the present invention includes two detection electrodes facing each other with a charged body in between, two vibrating bodies that vibrate these detection electrodes perpendicularly to the surface of the charged body at different frequencies, and an output of the detection electrodes. It consists of two band-pass filters that extract only the vibration frequency components from each band, and voltage measuring means that measures the output voltage that has passed through these band-pass filters.

[0011]

[Operation] FIG. 1 shows the principle of the present invention. Here, -σ1 and +σ2 are equivalent surface charge densities of the film-like charged body 3, +σ
1' and -σ2' are the surface charge densities induced on the detection electrodes 1 and 2, E is the electrolytic strength within the charged body 3, E1 and E2 are the electric field strengths between the detection electrodes 1 and 2 and the charged body 3, respectively. ε is the dielectric constant of the charged body 3, ε0 is the dielectric constant in air, h is the thickness of the charged body 3, and g1 and g2 are the detection electrodes 1 and 2 and the charged body 3, respectively.
S is the area of detection electrodes 1 and 2, R1 and R2 are load resistances, i1 and i2 are currents, and v1 and v2 are voltage drops. In the same figure, detection electrodes 1 and 2 are operated at respective frequencies ω1 and ω2 at the same time t,

0012

[Math 4]

Let us consider the case where the charged body is vibrated perpendicularly to the three planes, that is, parallel to the lines of electric force, so that the charged body vibrates in parallel to the lines of electric force. Here, g10 and g20 are the intervals when the detection electrodes 1 and 2 are stationary, respectively, and Δ1 and Δ2 are the amplitudes of the detection electrodes 1 and 2, respectively. Figure 1 shows the law of conservation of charge, Kirchhof
Applying the second law of f, Gauss's law, we get

[0014]

[Math 5]

[0015]

[Math 6]

[0016] For v2,

0
017]

[Math 7]

A nonparametric differential equation is obtained. this is,

[0019]

[Math. 8]

We have the following solution. here,

[0021]

[Math. 9]

[0022]

[Math. 10]

[0023]

[Math. 11]

[0024]

[Math. 12]

[Math. 13]

In such a case, if Δ1 and Δ2 are known, the components of v2, a21sin(ω1t+θ1) and a
By extracting 22sin(ω2t+θ2) with separate bandpass filters, the charged body 3 is extracted from a21 and a22.
The surface charge densities σ1 and σ2 of can be determined.

Δ1 and Δ2 are known voltages V as shown in FIG.
It can be determined using a simulated charged body (conductor plate) 4 given c. In FIG. 2, g is the distance between the detection electrode 1 or 2 and the simulated charged body 4, R is the load resistance, S is the area of the detection electrode 1 or 2, i is the current, and v is the voltage drop of R. Now, the detection electrode 1 or 2 is set at an amplitude Δ and each frequency ω with g0 as the center.

[0027]

[Math. 14]

Suppose that it is vibrated as follows. In this case, if

[0029]

[Math. 15]

[0030] Then, the output voltage v is

[0031]

[Math. 16]

[0032] here

[0033]

[Math. 17]

[0034]

[Math. 18]

[0035]

[Math. 19]

By measuring the amplitude a of v, Δ can be obtained from Equation 14. This Δ is Δ1 when the detection electrode is 1
Then, when it is 2, it becomes Δ2.

[0037]

Embodiment FIG. 3 shows an embodiment of the measuring device according to the present invention. The first and second detection electrodes 1 and 2 are attached to speakers 5 and 6 via support columns 1a and 2a, respectively, and are opposed to each other with the charged body 3 in between. The moving coils 5a, 6a of the speakers 5, 6 are given signals of different frequencies from the oscillators 7, 8, and both the detection electrodes 1, 2 are vibrated perpendicularly to the surface of the charged body 3, that is, longitudinally vibrated parallel to the lines of electric force. let For example, the first detection electrode 1 is vibrated at 659.5 Hz, and the second detection electrode 2 is vibrated at 286 Hz. The load resistances R1 and R2 between each of the detection electrodes 1 and 2 and the ground are, for example, 100KΩ. Further, it is assumed that the distance g1 between the detection electrode 1 and the charged body 3 and the distance g2 between the detection electrode 2 and the charged body 3 are the same (g1=g2=g0).

A voltage appears on the second detection electrode 2 in accordance with the surface charge density on one surface of the charged body 3 and the surface charge density on the other surface. After amplifying this voltage with the voltage amplifier 9,
Only the respective vibration frequency components are extracted by the first and second bandpass filters 10 and 11. In this example, the pass frequency of the first bandpass filter 10 is 659
．． The pass frequency of the second bandpass filter 10 is 286 Hz.

The analog outputs of these first and second bandpass filters 10 and 11 are converted to A/D converters 12 and 1.
After converting them into digital data in step 3, the CPU 14 calculates them in real time. Now, it is assumed that the output voltages obtained from the first and second bandpass filters 10 and 11 are V1 and V2, respectively. Further, in FIG. 3, if the combined gain of the voltage amplifier 9 and the first bandpass filter 10 is A1, and the combined gain of the voltage amplifier 9 and the second bandpass filter 11 is A2, then V1, V2 and , a21 given by the above equation 6, and a22 given by the above equation 11, the following relationship holds true. V1=A1a21 V2=A2a22

00
40] Therefore, the load resistances R1 and R2 which are default values included in a21 and a22, the distance g0 and the detection electrode 1,
2 amplitudes Δ1 and Δ2, and further default values of gains A1 and A
2 is stored in the RAM 15, and the voltages V1 and V2 are
By importing and calculating according to a program stored in the ROM 16 or external storage means, the surface charge densities σ1 and σ2 on both sides of the charged body 3 can be determined in real time. According to one experimental example conducted by the present inventors, when the distance g0 is 1.5 mm, σ1 is 12.3×10-4C/m2
, σ2 was 12.8×10 −4 C/m 2 .

In FIG. 3, voltage comparators 17 and 18 and a sign determination circuit 19 are used to determine the charging polarity of the charged body 3, and the light emitting element 20 blinks according to plus or minus.

FIG. 4 shows an example of measurement in which the amplitudes of the detection electrodes 1 and 2 are measured in advance using the simulated charged body 4. here,
Both detection electrodes 1 and 2 have a diameter of 5.5 mm, and detection electrode 1 has a diameter of 6 mm.
The vibration frequency was 59.5 Hz, and the detection electrode 2 was vibrated at 286 Hz. Then, as measured by the memory scope 21, the number 13 is
When a was determined from the formula, and the amplitudes Δ1 and Δ2 of the detection electrodes 1 and 2 were determined from the equation 14, the results shown in FIG. 5 were obtained depending on the change in the distance g0. From this figure, when g0=0, Δ1=7 μm, Δ
It can be estimated that 2=8 μm.

[0043]

[Effects of the Invention] According to the present invention, the charges on both surfaces of a charged body can be measured simultaneously and instantaneously in real time even during movement, so for example when measuring the charge density on both sides of a moving film. suitable for

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is a diagram explaining the principle of measuring the amplitude of a detection electrode using a simulated charged body.

FIG. 3 is a block diagram of an embodiment of the measuring device of the present invention.

FIG. 4 is a schematic diagram of an example of measuring the amplitude of a detection electrode using a simulated charged body.

FIG. 5 is a graph showing the relationship between the measured amplitude and the distance between the charged body and the detection electrode.

FIG. 6 is a block diagram showing a measurement method using a conventional distance-compensated electrometer.

[Explanation of symbols]

1 First detection electrode 2 Second detection electrode 3 Charged body 4 Simulated charged body 5 Speaker 6 Speaker 5a Moving coil 6a Moving coil 11 First bandpass filter 12 Second bandpass filter 14 CPU

Claims (4)

[Claims] Claim 1: Two detection electrodes are placed opposite to each other with a charged body in between and vibrated perpendicularly to the surface of the charged body at different frequencies, and the outputs of these detection electrodes are measured via a filter corresponding to the vibration frequency. A method for measuring surface charge density, characterized by: 2. The method for measuring surface charge density according to claim 1, wherein the amplitude of the detection electrode is measured in advance using a simulated charged body. 3. Two detection electrodes facing each other with a charged body in between, two vibrating bodies that vibrate the detection electrodes perpendicularly to the surface of the charged body at different frequencies, and the vibration frequency component obtained from the output of the detection electrodes. What is claimed is: 1. A surface charge density measuring device comprising: two band-pass filters for extracting only two band-pass filters, and a voltage measuring means for measuring output voltages passed through these band-pass filters. 4. The surface charge density measuring device according to claim 3, wherein the vibrating body is a moving coil.