JPS6365907B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a static electricity detector that detects static electricity in a fluid such as a charged liquid, gas, or powder.

The present applicants have developed a current collector and output circuit having a radioactive substance as shown in FIG. A built-in current collecting type static electricity detection probe 1 is fixedly placed (fixed so as not to move) inside a metal ball 3 whose outer circumferential surface is coated with a thin insulating coating 2, and the static electricity induced in this metal ball 3 is absorbed by radiation ionization. A device has already been proposed (known in Japanese Patent Publication No. 1791/1982) in which current is collected by a current collector and an electrical signal corresponding to the potential is output from an output circuit.

In this device, the insulating coating 2 is applied to the metal ball 3 in order to prevent corona discharge or spark discharge between the metal ball 3 and an external charged object. However, there is a concern that the detection accuracy will be worse than those without this.

This is due to the following reasons.

That is, when the insulation coating 2 is applied, a capacitance is generated therein, and this capacitance is called C ₁ and the so-called capacitance between the grounded cylindrical case (grounded outer cylinder) of the static electricity detection probe 1 and the metal ball 3. stray capacitance
C ₂ , R ₁ is the leakage resistance between the metal ball 3 and the ground, R 2 is the resistance of the electric circuit formed in the space between the current collector and the metal ball 3 due to radiation ionization, and R ₂ is the current collector input resistance. If the resistance to keep constant is R ₃ , then
An equivalent circuit as shown in FIG. 2 is established between the charged object and the current collector. Note that Vi is an input potential (charged potential) and Vo is an output potential (current collector detection potential).

As is clear from this equivalent circuit, the insulation coating 2
When capacitance C ₁ is generated by , the time constant of the circuit changes, and the output characteristics of Vo change, that is, the responsiveness of the current collector to the charging potential deteriorates.

In order to improve this, the present inventors have conducted various tests and research, and based on the following experimental results, the insulation coating 2
It was discovered that it is possible to produce output characteristics similar to those without insulation coating even if insulation coating is applied, and based on this, this book makes it possible to easily compensate for the disadvantages mentioned above due to insulation coating. It is the invention that was devised.

That is, the present inventors have developed a structure shown in FIG. 1 that is provided with an insulation coating 2 (hereinafter referred to as an insulation coating bulb), and a structure that is different from the structure shown in FIG. 1 except that this is not provided. The insulated bulb is made with a bulb of substantially the same configuration as that (hereinafter referred to as a bare bulb), and the metal bulb 3 is grounded with a high resistance as shown in the equivalent circuit of Figure 3. Connect the resistor (ground resistance) R′ ₁ positively and change its value.
10 ¹² Ω, 10 ¹⁵ Ω, and 10 ¹⁵ Ω, leave the other bare bulb unconnected, charge both bulbs to the same predetermined potential, and then connect the outputs of both static electricity detection probes. Each was measured.

Figure 4 shows its output characteristics (attenuation transition due to charge movement after being charged to a predetermined potential), where the curve marked with an x indicates the output of the insulated bulb, and the curve marked with an ○ indicates the output of the bare bulb. are shown respectively.

As can be seen from this figure, the output characteristics of the insulated bulb change depending on the resistance value of the grounding resistance R' ₁ , and when the grounding resistance R' ₁ is 10 ¹³ Ω, the output characteristics of the insulated bulb become almost equal to the output characteristics of the bare bulb. There is.

This means that by choosing an appropriate value for grounding resistance R′ ₁ ,
Change the time constant of the circuit to one without capacitance C ₁ (bare bulb)
This proves that if you make it the same as that of a bare bulb, you can get the same output characteristics as a bare bulb.

Therefore, by connecting the grounding resistor R' ₁ to the metal ball 3 of the insulation-covered bulb shown in Fig. 1 and adjusting its value, the detection accuracy of the insulation-covered bulb can be made equal to that of a bare bulb. You will be able to do that.

However, as is clear from the above, the output characteristics cannot be adjusted unless the ground resistance has a high value of 10 ¹² to ^{10 15} Ω, and it is not possible to mass-produce products with the same detection accuracy by adjusting this value. In reality it is very difficult.

Therefore, in the equivalent circuit shown in FIG. 2, the inventors have discovered that the time constant of the circuit can also be adjusted by the resistor R ₂ (resistance of the electric circuit formed by the action of radiation ionization). It was confirmed through experiments that this resistance R ₂ could be adjusted, and by providing a means for adjusting this resistance R 2 in a conductive hollow body (corresponding to the metal sphere 3 in Figure 1), it was possible to make it different from a bare sphere. The present invention has been devised so that it is possible to easily produce products with the same detection accuracy.

The present invention will be described in detail below with reference to the embodiment shown in FIG.

This static electricity detector has a conductive hollow body 4 made of a bowl-shaped metal, for example, aluminum.
A thin (0.5 to 0.8 mm thick) insulating coating 5 is applied, and the upper opening of the conductive hollow body 4 is closed with a thick disk-shaped insulating support 6, and a current collecting type static electricity detection device is installed on this insulating support 6. It supports the probe 7.

For the insulating coating 5 and the insulating support 6, it is preferable to use a synthetic resin that is highly insulating and has good oil resistance. In this example, the material of the insulation coating 5 is an epoxy thermosetting resin, and the material of the insulation support 6 is glass fiber-filled epoxy resin (FRP).

The insulating support base 6 connects its male screw 8 to the conductive hollow body 4
By screwing into the female thread 9 of the conductive hollow body 4, the upper opening of the conductive hollow body 4 is closed in a liquid-tight manner. Therefore, a liquid-tight space 10 is formed within the conductive hollow body 4 .

The bottom surface 11 of the liquid-tight space 10, which is the inner surface of the conductive hollow body 4, is a horizontal plane without sharp parts. The other surfaces of the liquid-tight space 10 are also smooth surfaces with no sharp parts.

The static electricity detection probe 7 has a current collector 14 supported on an insulating support 13 in a metal cylindrical case (grounded outer case) 12, an output circuit mounted on a circuit board 15, and this output circuit connected to a coupling resistor. 1
6 is connected to a current collector 14, and the current collector 14 is connected to the cylindrical case 12 via a high resistance 17. The current collector 14 contains americium Am241 (8.8 μCi), which is a radioactive substance. The detection signal obtained by the current collector 14 is amplified and impedance-converted by an output circuit, and then outputted to the outside via a cable 18 connected to this output circuit.

The static electricity detection probe 7 having such a structure has its cylindrical case 12 attached to the mounting hole 19 in the center of the insulating support base 6.
The cylindrical case 12 is inserted in a vertically slidable manner so that the radiation (α rays) from americium is irradiated straight onto the bottom surface 11 of the liquid-tight space 10, and the cylindrical case 12 is inserted into the mounting hole 19 so as to be vertically slidable. By adjusting the insertion position up and down, the distance between the current collector 14 and the bottom surface 11 can be adjusted. Vertical sliding of the cylindrical case 12 with respect to the mounting hole 19 is controlled by a recess 20 formed at the upper opening edge of the mounting hole 19.
It is regulated by a gasket 21 fitted in the.

The upper end of the cylindrical case 12 protrudes from the upper end opening of the mounting hole 19, and the upper end is connected to a protective ring 23 made of an insulating material screwed to the upper surface of the insulating support base 6 via a packing 22. The protection ring 23 is liquid-tightly covered by a cover plate 24 made of an elastic material such as rubber and screwed onto the top surface of the protection ring 23.
In this example, the protective ring 23 is made of the same material as the insulating support base 6.

A truncated conical radiation opening 25 is formed on the lower surface of the insulating support base 6 and continues to the mounting hole 19.
The tip opening (lower end opening) of No. 2 is located at the upper end of this radiation opening portion 25 .

Inside the radiation port 25 is a funnel-shaped insulating member 26 made of an insulating material whose insulation properties are somewhat inferior to that of the insulating support base 6.
is embedded. In this example, this insulating member 2
The material of the insulating member 26 is phenol resin, and while the resistivity of the insulating support base 6 made of glass fiber-containing epoxy resin is 10 ¹⁴ Ωcm, that of the insulating member 26 is 10 ¹¹ to 10 ¹² Ωcm. .

A metal diaphragm plate 27 is removably screwed onto the lower end opening of the cylindrical case 12 to substantially reduce the opening area. This aperture plate 27 has an aperture hole 28 in its center.

Therefore, the α rays emitted from the americium in the current collector 14 are irradiated onto the bottom surface 11 of the liquid-tight space 10, and the space between the current collector 14 and the bottom surface 11 is ionized, and an electric circuit is formed between them. It is formed.
The resistance R ₂ of this electric circuit (the equivalent circuit of this static electricity detector is shown in Fig. 6) depends on the distance l between the current collector 14 and the bottom surface 11, and as l increases, R ₂ also increases. Therefore, as l becomes smaller, R ₂ also becomes smaller. Therefore, by vertically adjusting the insertion position of the cylindrical case 12 with respect to the mounting hole 19, R ₂ can be adjusted, and the time constant of the equivalent circuit can also be adjusted. Depending on the selection, the output characteristics can be made similar to those without the insulation coating 5. The ionization effect is weakened by the diaphragm plate 27, and the resistance in the equivalent circuit of FIG.
_R3 becomes higher. The degree of weakening is related to the size of the aperture hole 28, and the smaller the size, the stronger the degree of weakening. Therefore,
If you prepare a plurality of aperture plates 27 with different sizes of aperture holes 28 and use them interchangeably, the resistance will be reduced.
R ₃ can be adjusted and thus also the range of the measured potential (so-called range switching). Note that the resistance R ₂ changes slightly depending on the diaphragm plate 27 as well.

Since the entire inner peripheral surface of the liquid-tight space 10 is a smooth surface with no sharp parts, no corona discharge or spark discharge occurs therein, and since the bottom surface 11 is flat, α-rays are not generated. can be irradiated evenly, and the static electricity induced in the conductive hollow body 4 can be accurately collected in the current collector 14.

Furthermore, an insulating member 26 made of a material that has a lower resistivity and is less likely to be charged than the insulating support 6 is set around the outer periphery of the radiation port of the static electricity detection probe 7, that is, around the radiation port 25 of the insulating support 6. Therefore, there is no possibility that the insulating support base 6 is charged and the detection accuracy is deteriorated.

In the above embodiment, the resistance R ₃ can be adjusted by preparing a plurality of aperture plates 27 with different sizes of aperture holes 28 and using them interchangeably. Adjustment may also be made using a variable aperture plate that can change the aperture. Alternatively, adjustment may be made by replacing a plurality of wire meshes with different meshes (removably attaching them to the opening at the lower end of the cylindrical case 12).

As described above, the electrostatic detector of the present invention has a means within the conductive hollow body that can adjust the resistance of the electric circuit formed in the space between the current collector and the conductive hollow body by the action of radiation ionization. Therefore, it is possible to easily compensate for the disadvantage in detection accuracy due to the application of the insulating coating.

Further, as in the embodiment of claim 3, if the inner surface of the conductive hollow body and the portion to which radiation is irradiated is made flat, radiation can be irradiated evenly, and the conductive hollow body can be irradiated with radiation evenly. The induced static electricity can be accurately collected into a current collector.

Furthermore, as in the invention of claim 4, if a metal aperture plate or wire mesh with holes is arranged between the inner surface of the conductive hollow body and the current collector,
The measurement potential range can be easily adjusted.

Furthermore, as in the invention of claim 5, if an insulating member having a lower resistivity than the insulating support is attached around the opening at the tip of the insulating support,
Electrification in the periphery can be prevented, and detection accuracy can be further improved.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional example, Figure 2 is its equivalent circuit diagram, Figure 3 is an equivalent circuit diagram when a grounding resistor is connected to the metal ball, and Figure 4 is a conventional example in which the above-mentioned earthing resistor is connected. A graph showing experimental measurement data for comparing the output characteristics of the example and the structure without insulation coating, Fig. 5 is a cross-sectional view showing one embodiment of the present invention, and Fig. 6 is its equivalent circuit. It is a diagram. 14... Current collector, 7... Static electricity detection probe,
4... Conductive hollow body, 27... Aperture plate, 6... Insulating support base, 26... Insulating member.

Claims (1)

[Scope of Claims] 1. A current collecting type static electricity detection probe equipped with a current collector having a radioactive object and an output circuit is built into a conductive hollow body whose outer surface is coated with a thin insulation coating. In a static electricity detector that collects static electricity to a current collector by the action of radiation ionization and outputs an electrical signal according to the potential from an output circuit, the current collector and the conductive hollow are connected by the action of radiation ionization. A static electricity detector characterized in that the conductive hollow body is provided with means capable of adjusting the resistance of an electric circuit formed in a space between the body and the body. 2. The static electricity detector according to claim 1, wherein the means for adjusting the resistance is a member that supports the static electricity detection probe so as to be movable back and forth in the axial direction thereof. 3. The electrostatic detector according to claim 1, wherein the inner surface of the conductive hollow body, which is irradiated with radiation, is a flat surface. 4. A current collecting static electricity detection probe equipped with a current collector and an output circuit containing a radioactive object is built into a conductive hollow body with a thin insulating coating on the outer surface, and the static electricity induced in this conductive hollow body is converted into radiation ionization. Therefore, in a static electricity detector that collects current to a current collector and outputs an electric signal corresponding to the potential from an output circuit, the space between the current collector and the conductive hollow body is reduced due to the radiation ionization effect. means capable of adjusting the resistance of the electrical circuit formed in the
An electrostatic detector characterized in that the static electricity detector is provided in the conductive hollow body and includes a metal aperture plate or wire mesh provided with holes between the inner surface of the conductive hollow body and the current collector. 5. A current collecting static electricity detection probe equipped with a current collector containing a radioactive object and an output circuit is built into a conductive hollow body with a thin insulating coating on the outer surface, and the static electricity induced in this conductive hollow body is converted into radiation ionization. Therefore, in a static electricity detector that collects current to a current collector and outputs an electric signal corresponding to the potential from an output circuit, the space between the current collector and the conductive hollow body due to the radiation ionization action. A means for adjusting the resistance of an electric circuit formed therein is provided in the conductive hollow body, and the electrostatic detection probe is supported on the conductive hollow body by an insulating support, and the electrostatic detection probe is supported on the conductive hollow body by an insulating support. A static electricity detector characterized in that an insulating member having a resistivity lower than that of the insulating support base is provided on the inner surface around the tip opening of the static electricity detection probe.