JPS5921510B2 - Non-contact AC electrometer probe - Google Patents

Description

[Detailed Description of the Invention] The present invention modulates an electric field corresponding to the surface potential of an object to be measured using an electric field modulator consisting of a vibrating electrode, and obtains an electric field from a sensing electrode placed in the modulated electric field. In order to convert the displacement current into voltage using a current-voltage converter and output it, there is a casing that shields the entire electrostatic field from the external space, and a casing that protects the electric field generated by the object under test from one side of the casing. a sensing electrode held in place by an electric field shielding block and an insulating material for sensing through an aperture provided in an aperture plate; and a vibrating electrode provided between the sensing electrode and said aperture. This was done with the aim of achieving lower noise, higher accuracy, and no adjustment in a non-contact AC electrometer probe that includes an electric field modulator.

Reducing the noise of the probe of a non-contact AC electrometer is important from the perspective of improving measurement accuracy, so various methods have been used to achieve this goal. We have made various proposals regarding non-contact AC electrometers that generate noise.

Now, in a non-contact AC electrometer, the strength of the electric field (the amount of electric field) that reaches the detection electrode from the object to be measured through the aperture provided in the aperture plate on one side of the housing that electrostatically shields the entire body from the external space. is configured such that the surface potential of the object to be measured can be measured based on the magnitude of the displacement current obtained at the sensing electrode by temporally varying the current using an electric field modulator. Contact potential differences that occur at the junctions of dissimilar metals in mechanical parts or electrical circuits included in the system become noise that interferes with measurement results.

This point will be explained in detail as follows with reference to FIG. 1, which shows a side sectional view of the essential parts of an example of a probe of a conventional non-contact AC electrometer.

That is, in FIG. 1, o is the object to be measured, 1 is the casing,
Reference numeral 2 denotes an electric field modulator consisting of a vibrating electrode, 3 a detection electrode, 4 an electric field shielding block, and 5 a support made of an insulating material. In addition to the displacement current generated in the sensing electrode 3 in response to the electrolysis Es reaching the sensing electrode 3 through the aperture 1a provided in the plate, the vibrating electrode 2, etc., there is also a displacement current generated between each component of the probe. Displacement currents generated in each component of the probe and the sensing electrode 3 due to contact potential differences and other causes also appear. Generally, when dissimilar metals are brought into contact with each other, a contact potential difference occurs on the surface corresponding to the difference in the work functions of the two metals. When metal products used as parts such as the housing 1, the vibrating electrode 2, the sensing electrode 3, and the electric field shielding block 4 form one electric circuit, each of the constituent parts has a different work function. When the contact potential difference occurs between the component parts that are in contact with each other to form one electric circuit, the electric field generated by this contact potential difference occurs. ENi generates a displacement current that causes an error in the sensing electrode 3, and the displacement current 1 generated in the sensing electrode 3 increases the strength of the electric field reaching the sensing electrode 3 from the object to be measured 0 by Es, which reaches the sensing electrode 3. The effective passage area of the electric lines of force is Ss, the dielectric constant of vacuum is εo, the strength of the electric field reaching the sensing electrode 3 based on the contact potential difference is ENI, and its area is Ss.
When Ni is used, the result is expressed by the equation (1).

In this way, when the constituent parts of a non-contact AC electrometer are made of different metals, the difference in contact potential that occurs between the constituent parts causes errors in the measured values. . The above problem may be solved by using plating of the same metal for each component, but in conventional products in which each component is plated with the same metal, errors caused by contact potential differences occur. outbreaks remained a problem. In other words, in conventional products, some of the component parts are electroplated and some are chemically plated, and each component is Since the surface condition was made with various surface roughness,
Even if the surfaces of each component were plated with the same metal, the contact potential difference caused by the difference in work function due to the difference in surface condition caused a non-negligible error.

In addition, since pinholes are likely to occur in electroplating, the film must be thick in order to form a plated surface with a smooth surface without pinholes. If electroplating is used, not only will the cost be considerably high, but also the film thickness at the edges will be large, so that the electric field at the edges of the metals where there is a contact potential difference will be transferred to other parts. This results in disadvantages such as an even larger error.

The present invention has been made for the purpose of providing a probe for a non-contact AC electrometer that does not have the drawbacks of the conventional non-contact AC electrometer probes described above. The contents of the probe of the type electrometer will be explained in detail with reference to the attached drawings.

FIG. 2 is a side sectional view of a main part of an embodiment of the non-contact AC electrometer probe of the present invention, in which 1 is a housing, 2 is an electric field modulator consisting of a vibrating electrode, 3 is a detection electrode, 4 is an electric field shielding block, 5 is a support made of an insulating material, and the aperture plate of the casing 1 is provided with an aperture 1a.

The probe of the non-contact AC electrometer of the present invention described above includes each component such as the housing 1, the aperture plate of the housing 1, the electric field modulator 2 made of a vibrating electrode, the sensing electrode 3, and the electric field shielding block 4. As a result, small particles are formed on the surface of the material of each component such as the housing 1, the aperture plate of the housing 1, the electric field modulator 2, the sensing electrode 3, and the electric field shielding block 4, which have approximately the same surface roughness. It is constructed using a uniform and smooth chemically plated layer of the same metal (for example, gold, silver, etc.) that has a tendency to ionize.

The probe of the non-contact AC electrometer of the present invention having the above-mentioned structure has each of the above-mentioned constituent parts uniform and smooth without any piholes that cause surface corrosion.
Since they are coated with the same metal layer that has a small ionization tendency, the surfaces of each of the above components remain stably in the same state over a long period of time, and their work functions do not change. Therefore, no contact potential difference occurs between the metal surfaces of each of the above-mentioned constituent parts.

Therefore, the displacement current appearing in the sensing electrode 3 due to the electric field ENi based on the contact potential difference shown in the second term on the right side of equation (1) above also becomes zero, and the non-contact AC electrometer of the present invention In the probe, errors caused by contact potential differences can be eliminated, and the above-mentioned problems with conventional non-contact AC electrometer probes can be successfully solved by the non-contact AC electrometer probe of the present invention. It will be done. The above-mentioned non-contact AC electrometer probe of the present invention includes a housing 1, an aperture plate of the housing 1, an electric field modulator 2 consisting of a vibrating electrode, a sensing electrode 3, and an electric field shielding block 4.
In other words, the surface of each component of a material with approximately the same surface roughness is provided with a uniform and smooth chemically plated layer of the same metal (e.g., gold, silver, etc.) that has a small tendency to ionize. Each component can be made as follows, for example.

That is, a housing 1, an aperture plate of the housing 1, an electric field modulator 2, and a sensing electrode 3 in a probe of a non-contact AC electrometer.
, electric field shielding block 4, etc., each surface of the material has the same surface condition (
For example, wrapping (
The finished component is then chemically plated with the same metal (eg, gold or silver) with a low ionization tendency.

Housing 1 of the above-mentioned non-contact AC electrometer probe
, an aperture plate of the housing 1, an electric field modulator 2, a sensing electrode 3,
Surface treatment by lapping (or other polishing means) to be performed on the surface of the material of each component such as the electric field shielding block 4 is preferably done to a state close to mirror polishing, and it is also preferable that the ionization The metal layer formed by chemical plating with metals having the same tendency has a film thickness of, for example, 3 to 3.
The thickness is preferably about 5 microns.

In addition, when performing the chemical plating described above, a plating layer is formed by chemical nickel plating as a base to smooth the surface condition, and then a thin film of a metal with a low ionization tendency is applied by chemical plating with a metal with a low ionization tendency. may be formed.

As is clear from the detailed explanation above, in the non-contact AC electrometer probe of the present invention, the surface of each component is coated with a chemically plated layer of the same metal that has a small ionization tendency. Furthermore, since the surface is smooth, there can be no difference in contact potential between the constituent parts, and the problems of the prior art can be satisfactorily solved.

It goes without saying that even better results can be obtained if the means described in Japanese Patent Application No. 55-35084 are used in conjunction with the construction of the probe of the non-contact AC electrometer of the present invention. Nor.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a part of an example of a conventional non-contact AC electrometer probe, and FIG. 2 is a side view of a main part of an embodiment of the non-contact AC electrometer probe of the present invention. FIG. 1... Housing, 2... Electric field modulator using a vibrating electrode, 3
...Detection electrode, 4...Electric field shielding block.

Claims (1)

[Claims] 1. A casing that electrostatically shields the entire body from external space, and an electric field shielding block and an insulating material to detect the electric field generated in the object to be measured through an aperture provided in an aperture plate on one side of the casing. In a probe of a non-contact AC electrometer, the probe includes a sensing electrode held at a predetermined position by a sensor, and an electric field modulator consisting of a vibrating electrode provided between the sensing electrode and the aperture. ,
Each component of the above-mentioned casing, aperture plate of the casing, electric field shielding block, sensing electrode, vibrating electrode, etc. is made of the same material that has a small ionization tendency on the surface of the material that has approximately the same surface roughness. A non-contact AC electrometer probe constructed using a metal with a uniform and smooth chemically plated layer.