JP7440025B2 - Static elimination mechanism - Google Patents

Description

The present invention relates to a static elimination mechanism that does not generate ignition discharge.

Many ignition accidents in hazardous locations where flammable solvents or powders are handled are caused by ignitable discharges that occur between a charged conductor and a grounded conductor due to poor grounding.
Accidents caused by such ignitable discharge can be prevented by properly removing static electricity from objects or grounding them, which is the basis of static electricity countermeasures.

In the conventional static elimination mechanism, a terminal maintained at a ground potential is brought into direct contact with the object to remove static electricity from the object.
In addition, for explosion-proof measures, it is necessary to check whether the target object is grounded. This is because if the object is electrically charged due to insufficient grounding, sparks may cause an accident.

Therefore, conventionally, for example, one of a pair of terminals was brought into contact with the object and the other terminal was brought into contact with the ground side to eliminate static electricity. Further, to determine whether or not an object is grounded, a terminal is brought into contact with the object, a voltage is applied to the terminal, and it is determined whether a current flows through the object.

JP2015-204234A Japanese Patent Application Publication No. 2016-225244

In the conventional static elimination mechanism described above, a terminal that maintains the ground potential is brought into direct contact with the object to be neutralized, so immediately before the terminal comes into contact with the object to be neutralized, dielectric breakdown occurs between the object to be neutralized and the terminal. occurs, and at that time, excessive discharge energy is released. Therefore, an ignitable spark discharge occurs between the object to be neutralized and the terminal.

If a spark discharge occurs between the object to be neutralized and the terminal as described above, it may cause an explosion or fire accident.
In other words, the conventional static eliminator mechanism has the contradiction that, although it removes static electricity from the object to be neutralized, the static eliminator itself can cause explosions and fires.

Furthermore, with conventional grounding confirmation devices, a terminal is brought into contact with the object to be measured, and a voltage is applied to the terminal to determine whether or not a current flows; therefore, it does not have a function to eliminate static electricity from the object to be measured in advance. Ta.
Therefore, like the above-mentioned static eliminator mechanism, although it is a device for checking grounding, it has the contradiction of creating a cause for ignition itself.

An object of the present invention is to provide a static elimination mechanism that does not cause explosions or fires.

The most important feature of the static elimination mechanism of the present invention is that when dielectric breakdown occurs between the tip of a conductor such as a terminal and the object to be neutralized, a high-resistance element blocks the flow of a large current, and the conductor The point is that the object to be neutralized and the conductor have the same potential due to the charge stored in the stray capacitance on the side.

In the above configuration, the stray capacitance is determined by the facing length between the conductor and the grounded casing serving as the stray capacitance generating means. Therefore, by setting the opposing length, stray capacitance can be kept small. If the stray capacitance is minute, even if the dielectric breakdown described above occurs, only a discharge current corresponding to the amount of charge stored in the stray capacitance will flow momentarily, and the conductor and the object to be neutralized will immediately reach the same potential. Become.
The stray capacitance is determined by the opposing length between the conductor and the stray capacitance generating means as described above, and this opposing length also changes depending on the cross-sectional shape of the conductor. For example, if the conductor has a flat cross section or a circular cross section and a large diameter, the length can be relatively shortened.

If the conductor and the object to be neutralized have the same potential in this way, no discharge current will flow between the conductor and the object.
Therefore, the discharge current flowing between the conductor and the object becomes very small, corresponding to the small amount of electricity stored in the stray capacitance. If the discharge current is small in this way, the discharge energy will also be small, so ignitable discharge can be prevented.

Furthermore, if the charge stored in the stray capacitance is discharged and a potential difference is created again between the object and the tip of the conductor, the discharge due to dielectric breakdown will be repeated each time. However, as described above, the discharge current at that time is minute, so even if charging and discharging are repeated, the discharge energy is small and does not lead to ignitable discharge.

The conductor may be a metal, a conductive resin or a conductive ceramic having a certain degree of resistance, or a combination of a metal and a conductive resin or a conductive ceramic. However, in the case of resin or ceramics, it is required to have sufficient conductivity to allow static electricity from the object to be neutralized to escape to the ground potential holding means.
Moreover, the structure and material of the ground potential holding means are not limited as long as they maintain the same potential as the ground.

Furthermore, when dielectric breakdown occurs between the tip of the conductor and the object to be neutralized, the high-resistance element momentarily blocks the flow of a large current, and the stray capacitance is transferred to the object to be neutralized. It performs the function of storing electric charge until it reaches the same potential as the object. Therefore, this high-resistance element has the function of accumulating electric charge in the stray capacitance and, after the tip of the conductor comes into contact with the object to be neutralized, to flow the static electricity of the object to the ground side.

Further, in the static elimination mechanism of the present invention, the opposing length of the conductor and the stray capacitance generating means is maintained at a length such that the stray capacitance is 0.1 pF to 5 pF, and the high resistance element is set to 100 MΩ to 500 MΩ. It is something.

According to the static elimination mechanism of the present invention, even if discharge occurs due to dielectric breakdown between the object to be neutralized and the tip of the conductor, the discharge energy at that time can be suppressed to a small level, so that ignitable discharge can be prevented.

It is a schematic diagram of the structure of a static elimination mechanism. FIG. 2 is a schematic diagram showing an example in which the static elimination mechanism is used in a current measuring device. FIG. 3 is a sectional view of the grounding confirmation device. FIG. 3 is a circuit diagram of a grounding confirmation device.

The embodiment shown in FIG. 1 is a schematic diagram of a static elimination mechanism, which includes a grounded casing A, and has a pointed end of a conductor 1 protruding from an opening of the casing A. This conductor 1 is connected to a high resistance element 2 on the opposite side from its tip, and this high resistance element 2 is grounded via a cable x.

Although the cable x grounded as described above constitutes the ground potential holding means of this invention, in this invention, any structure, material, etc. may be used as long as it maintains the ground potential. do not have.

When a voltage is applied to the conductor 1 as described above, a stray capacitance SC is generated between the conductor 1 and the grounded casing A. In this embodiment, the conductor 1 and the casing A are arranged to face each other so that a stray capacitance SC is generated between them .

The stray capacitance SC is determined depending on the opposing length L between the conductor 1 and the casing A, but it is desirable to make it as small as possible.
If the capacitance of the stray capacitance SC is minute in this way, even if dielectric breakdown occurs between the tip of the conductor 1 and the object 11 to be neutralized, the conductor and the object 11 to be neutralized will instantly have the same potential. Only the current corresponding to the amount of electricity stored in the stray capacitance flows.
Furthermore, if the stray capacitance SC has a small capacity, charging and discharging will be repeated in a short period of time, but since the current that flows due to such repeated charging and discharging is also sufficiently small, the discharge energy will also be small.

The stray capacitance SC is determined by the opposing length L between the conductor 1 and the casing A, which is the stray capacitance generating means, as described above, but this opposing length L also changes depending on the cross-sectional shape of the conductor 1. For example, if the conductor has a large opposing area, such as a conductor with a flat cross-section or a large diameter, its length can be relatively shortened.

Furthermore, in Fig. 1, the distance from the tip of the conductor 1 protruding from the casing A to the high resistance element 2 is set as the facing length L, but if the protruding end of the conductor 1 is close to the casing A, the stray capacitance SC affect. Therefore, in FIG. 1, the opposing length from the tip of the conductor 1 to the high resistance element 2 is set as L.

Furthermore, the high-resistance element 2 suppresses the flow of current at the time of the dielectric breakdown and stores electricity in the stray capacitance SC. All you have to do is maintain a resistance value that allows the flow to flow smoothly through cable x.

For example, when the stray capacitance is set to a minute value of about 3 pF and the resistance value of the high resistance element 2 is set to about 100 MΩ, the time constant τ is 0.3 ms, so 3 pF and 100 MΩ are sufficiently allowable. .
However, the smaller the stray capacitance SC, the better. This is because if the stray capacitance SC is small, the discharge energy at the time of dielectric breakdown can be reduced. However, if the minimum ignition energy of the combustible substance is large, the capacity of the stray capacitance SC may be increased accordingly. In reality, it can be said that a range of 0.1 pF to 5 pF is within the permissible limit.

Further, the higher the resistance value of the high resistance element 2 is, the better in order to store the stray capacitance SC. However, when considering the static elimination of the static elimination target 11, there is a limit to its size. Its upper limit is about 500 MΩ, considering the time constant τ.

The static elimination mechanism configured as described above brings the tip of the conductor 1 together with the casing A close to the object 11 to be neutralized. When dielectric breakdown occurs between the tip of the conductor 1 and the object 11 for static elimination during this approach process, a current flows between the two. At this time, since the resistance value of the high resistance element 2 is large, charge is stored in the stray capacitance SC until it reaches the same potential as the object 11 to be neutralized. However, since the capacitance of this stray capacitance SC is small, the potential at the tip of the conductor 1 instantly becomes the same potential as the object 11 to be neutralized.

Since the tip of the conductor 1 and the object 11 to be neutralized instantly become at the same potential, the discharge current that flows becomes extremely small.
In addition, if the charge stored in the stray capacitance SC decreases due to discharge, discharge destruction occurs again, and the discharge destruction is repeated each time the potential difference between the tip of the conductor 1 and the object 11 to be neutralized increases. Since the discharge current due to breakdown is also small, ignitable discharge does not occur.

FIG. 2 is a schematic diagram of the case where the static elimination mechanism as described above is used together with a current measuring device.
That is, in FIG. 2, the electric current is measured by the tester T after the electric charge is removed from the object to be measured 11 by the electric charge removing mechanism as described above.
Note that it goes without saying that the tester T and the static elimination mechanism may be provided integrally.

The grounding confirmation device shown in FIGS. 3 and 4 includes a grounded casing A, and the tip of the conductor 1 protrudes from the opening of the casing A. The conductor 1 is connected to a conductive rod-shaped body 3 via a high-resistance element 2, and the conductive rod-shaped body 3 is covered with an insulator 4. Further, a plate-shaped switching element 5 is fixed to an end of this conductive rod-shaped body 3, that is, an end on the opposite side from the conductor 1.
The conductor 1, high resistance element 2, and conductive rod-shaped body 3 configured as described above are each movable integrally in the axial direction.

Further, a plate-shaped grounding element 6 is fixed to the casing A, and this grounding element 6 is always grounded via the casing A. The conductive rod-like body 3 integrated with the insulator 4 is made to penetrate through this grounding element 6 and protrude to the side opposite to the conductor 1, and the switching element 5 is fixed to the protruding end of the conductive rod-like body 3. It is electrically connected to the switching element 5.
A spring receiving plate 7 made of an insulating material is fixed in the casing A facing the grounding element 6, and a spring member 8 is interposed between the spring receiving plate 7 and the switching element 5.

Therefore, the spring force of the spring member 8 normally brings the switching element 5 into contact with the grounding element 6, and the conductor 1 is electrically connected to the grounding side via the switching element 5 and the grounding element 6.
Further, a measurement power supply circuit 9 is provided on the opposite side of the grounding element 6 with the spring receiving plate 7 as a boundary, and a conductor coupling element 10 electrically connected to the measurement power supply circuit 9 is provided. The tip of this conductor connection element 10 is opposed to the switching element 5 which is in contact with the grounding element 6 with a distance maintained therebetween.

With the above structure, the switching element 5 normally contacts the grounding element 6 under the action of the spring force of the spring member 8, thereby conducting the conductor 1 to the ground side. Therefore, when the conductor 1 is brought into contact with the illustrated measurement object 11, the object 11 is connected to the ground side and static electricity is removed.

In the above state, if the conductor 1 is pressed even more strongly against the object to be measured 11, the switching element 5, which moves integrally with the conductor 1, moves against the spring force of the spring member 8, and is separated from the grounding element 6. At the same time, the switching element 5 contacts the conductor coupling element 10 and connects the conductor 1 to the measurement power supply circuit 9 .

Therefore, the process of bringing the conductor 1 into contact with the object to be measured 11 to remove static electricity, and the process of separating the conductor 1 from the grounding element 6 and connecting it to the measurement power supply circuit 9 can be realized by a series of operations.
Note that, as is clear from the above, the switching element 5, the grounding element 6, the spring member 8, and the conductor connecting element 10 each constitute the switching mechanism of the present invention.

Further, this earthing confirmation device is also equipped with exactly the same mechanism as the static elimination mechanism described above. That is, it includes a grounded casing A, a conductor 1 facing the casing A, a high resistance element 2, and a grounding element 6 as a ground potential holding means. In order to perform the static elimination function, the functions of each of the above-mentioned components are also the same as those of the static elimination mechanism described above.
Therefore, in this grounding confirmation device, the description of the static elimination mechanism is used for the grounded casing A, the conductor 1 facing the casing A, the high resistance element 2, and the grounding element 6 as a grounding potential holding means.

On the other hand, as shown in FIG. 4, the measurement power supply circuit 9 includes a capacitor C as a measurement power supply, a voltmeter V as a measuring means of the present invention for detecting the voltage of the capacitor C, and a voltmeter V for storing electricity in the capacitor C. A DC power supply 12, an interlocking switch 13 that opens and closes between the power supply 12 and the capacitor C, and a manual switch 15 that opens and closes between the interlocking switch 13 and the capacitor C are provided.

The interlocking switch 13 is interlocked with the switching element 5 via an interlocking means 14. That is, when the switching element 5 is in contact with the grounding element 6, the interlocking switch 13 is closed, the capacitor C is connected to the power source 12, and the capacitor C is charged.

Further, when the switching element 5 moves against the spring member 8, the switching element 5 and the grounding element 6 are separated, and the switching element 5 and the conductor connecting element 10 maintain a contact state. In this contact state, the interlocking switch 13 opens, the charging of the capacitor C by the power supply 12 is interrupted, and the electric charge stored in the capacitor C flows to the measurement object 11 via the conductor 1.

In the above-described grounding confirmation device, in a state where the conductor 1 is in contact with the object to be measured 11, that is, in a normal state, the switching element 5 is in contact with the grounding element 6 due to the spring force of the spring member 8. The conductor 1 is connected to the ground side, and the interlocking switch 13 is closed as shown in FIG. 4 to charge the capacitor C.

When the conductor 1 is brought close to the object to be measured 11 in the above state, dielectric breakdown may occur depending on the amount of charge on the object to be measured 11, and a discharge occurs from the object to be measured 11 to the conductor 1. The principle of energy reduction is the same as that of the static elimination mechanism.

Furthermore, when the tip of the conductor 1 is moved and brought into contact with the object to be measured 11, the object to be measured 11 is grounded via the grounding element 6, so that the object 11 is neutralized. Since the object 11 is thus neutralized in advance, the charge will not flow into the measurement power supply circuit 9 and destroy it or cause it to catch fire.

In particular, the power supply voltage of the measurement power supply circuit 9 is set to a very low value in consideration of explosion-proof measures, and is normally assumed to be around 5V. Therefore, it is extremely significant to eliminate the charge from the measurement object 11 in advance to prevent the charge from flowing to the measurement power supply circuit 9 as described above.
Note that this embodiment has both the function of eliminating static electricity from the measurement object 11 in advance and the function of preventing current from flowing back into the measurement power supply circuit 9 due to the resistance of the high-resistance element 2.

When the conductor 1 is brought into contact with the object to be measured 11 as described above and then pressed even harder, the conductor 1 pushes the switching element 5 through the conductive rod-shaped body 3 against the spring force of the spring member 8, causing the switching The element 5 is separated from the grounding element 6, and the switching element 5 is brought into contact with the conductor coupling element 10.

Further, in the process in which the switching element 5 contacts the conductor coupling element 10 as described above, the interlocking means 14 pushes the interlocking switch 13 open, so that charging of the capacitor C is interrupted and the electric charge stored in the capacitor C is is guided to the conductor 1 via the conductor connection element 10, the switching element 5, the conductive rod-shaped body 3, and the high resistance element 2. Then, the amount of charge on the capacitor C at this time is measured with a voltmeter V.

If the amount of charge in the capacitor C becomes zero, it can be inferred that all of the charge has flowed to the ground side via the object to be measured 11, so in this case it can be determined that the object to be measured 11 is grounded. . Conversely, if the amount of charge does not become zero, it can be determined that the measurement target 11 is in a state of poor grounding.

After completing the measurement as described above, the conductor 1 is separated from the object 11, but in the process, the switching element 5 remains in contact with the grounding element 6 for a short time. By maintaining the contact state in this way, the residual charge on the measurement object 11 after the measurement is completed can be discharged by flowing to the ground side.

In any case, the steps are as follows: until the conductor 1 is brought into contact with the object 11 to measure whether the grounding is good or bad, and after the measurement is completed, the residual charge on the object 11 is flowed to the ground side to complete static elimination. , can be performed continuously in a series of operations, and the continuity of this operation is also a major feature of this embodiment.

In this embodiment, the amount of charge of the capacitor C of the measurement power supply circuit 9 is measured, but for example, a battery may be used instead of the capacitor C as the measurement power supply. However, in this case, the grounding status of the object 11 is determined based on the magnitude of the current flowing from the battery.

However, when determining the grounding status based on the magnitude of the current, it becomes difficult to set a standard for the amount of current.
Therefore, it is more advantageous to determine the grounding condition based on whether or not the amount of charge in the capacitor C has become zero as in the above embodiment, as it allows for a clearer determination.

It is effective as a static elimination mechanism or grounding confirmation device to prevent ignition accidents in dangerous locations where flammable solvents and powders are handled.

DESCRIPTION OF SYMBOLS 1...Conductor, 2...High resistance element, x...Ground potential holding means, 5...Switching element, 6...Grounding element, 8...Spring member, 9...Measurement power supply circuit, 10...Conductor connection element, 11...Target, L ... Interval, SC... Stray capacitance, C... Capacitor, V... Voltmeter, 13... Interlocking switch, 14... Interlocking means

Claims (1)

a conductor having a sharp tip for contacting an object;
A high resistance element connected to this conductor,
Ground potential holding means connected to the high resistance element on the opposite side to the side connected to the conductor;
A grounded casing with the pointed tip protruding from the opening, surrounding the conductor and facing the conductor, and serving as a stray capacitance generating means.
Equipped with
While having a configuration in which the stray capacitance is determined by the opposing length of the conductor and the stray capacitance generating means,
A static elimination mechanism in which the opposing length of the conductor and the casing is such that the stray capacitance is 0.1 pF to 5 pF, and the high resistance element is 100 MΩ to 500 MΩ.

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