JP7568204B2 - Electrical property measuring equipment - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act The 44th National Conference of the Society of Electrostatic Engineers of Japan will be held on September 25, 2020.

This invention relates to a capacitance measuring device that measures electrical characteristics as attributes of a measurement object.

Metal containers placed in dangerous locations where flammable solvents or powders are handled have a large electrostatic capacitance, and the discharge energy generated when the electric charge stored there is discharged will also be large.
Furthermore, if the discharge energy is large, it is likely to exceed the minimum ignition energy of flammable substances in the atmosphere in which the measurement target (such as the above-mentioned metal container) is placed.
If the energy of the discharge from the measurement target exceeds the minimum ignition energy, the discharge exceeding this energy can cause an ignition accident.

Furthermore, if the object being measured is securely grounded, static electricity will not accumulate and there is no need to worry about dangerous discharges as described above. However, the leakage resistance value of the object being measured will vary depending on the material of the object being measured and its installation conditions, and if the resistance value is high, it may not be possible to securely ground the object being measured, even if grounding measures have been taken. In such cases, static electricity can cause ignition discharges.

Therefore, it was thought that if the attributes of the object being measured, such as capacitance and leakage resistance, could be known in advance, it would be easier to implement explosion prevention measures and prevent fire accidents.

Patent No. 4975824

As mentioned above, there is a strong demand for a device that can easily determine the electrical characteristic values of the object to be measured, such as capacitance and leakage resistance, in advance to ensure explosion-proof measures, but to date, no device has existed that meets this demand. In addition, a search of patent information did not reveal anything that meets the above demand.

The purpose of this invention is to provide an electrical characteristic measuring device that can easily grasp the electrical characteristic values, such as the capacitance and leakage resistance value, of the object being measured.

The capacitance measuring device of the first invention comprises a detection terminal for contacting the object to be measured, a capacitor connected to the detection terminal, a voltage detection means for detecting the potential of the capacitor, and a calculation means for calculating the potential detected by the voltage detection means. While the detection terminal is brought into contact with the object to be measured, the calculation means defines the potential of the capacitor detected by the voltage detection means before the detection terminal is brought into contact with the object to be measured as an initial potential, and defines the potential of the capacitor detected by the voltage detection means after the detection terminal is brought into contact with the object to be measured as a post-contact potential, and calculates the capacitance of the object to be measured based on the ratio between the initial potential and the post-contact potential.

A second invention comprises a detection terminal for contacting the object to be measured, a capacitor connected to the detection terminal, voltage detection means for detecting the potential of the capacitor, and calculation means for calculating the potential detected by the voltage detection means, wherein the detection terminal is brought into contact with the object to be measured, while the calculation means sets the potential of the capacitor detected by the voltage detection means before the detection terminal is brought into contact with the object to be measured as an initial potential, and sets the potential of the capacitor detected by the voltage detection means after the detection terminal is brought into contact with the object to be measured as a post-contact potential, and calculates the leakage resistance value of the object to be measured based on the decay time of the post-contact potential.

In a third aspect of the present invention, the capacitor is of a variable capacitance type.

A fourth aspect of the present invention includes a selection means for connecting a plurality of capacitors having different capacitances in parallel and selecting one of the capacitors as the capacitor.

The fifth invention is provided with a grounding element that is always kept in a grounded state, while normally connecting the detection terminal to the grounding element, and providing a switching mechanism that disconnects the detection terminal from the grounding element and connects the detection terminal to the capacitor when the detection terminal is pressed against the object to be measured and a pressing force acts on the detection terminal.

In a sixth aspect of the present invention, a high resistance element is connected to the detection terminal, and the detection terminal is connected to the ground element or the capacitor via the high resistance element.

In a seventh aspect of the present invention, the switching mechanism comprises a switching element which moves integrally with the detection terminal and is electrically connected to the detection terminal, the grounding element which is always maintained in a grounded state, and a spring member which applies a spring force to the switching element and brings the switching element into contact with the grounding element through the action of the spring force, and normally, the spring force of the spring member brings the switching element into contact with the grounding element to ground the detection terminal.

In an eighth aspect of the present invention, the switching mechanism comprises a switching element that moves integrally with the detection terminal in the axial direction of the detection terminal, and a conductor connecting element having one end that maintains a gap from the switching element and the other end that is electrically connected to the capacitor, and when the switching element moves the gap against the spring force of the spring member, the switching element and the capacitor are connected via the conductor connecting element.

The ninth invention comprises an interlocking switch provided between the capacitor and a power source for charging the capacitor, and interlocking means for interlocking the interlocking switch with the switching element, wherein the interlocking means closes the interlocking switch when the switching element is in contact with the grounding element and is disconnected from the capacitor, and the interlocking means opens the interlocking switch when the switching element is disconnected from the grounding element and is electrically connected to the capacitor.

The tenth invention is configured to specify a reference discharge energy that is less than the minimum ignition energy of a combustible substance in an atmosphere in which the object to be measured is used as a standard, while a floating capacitance is generated whose electrostatic capacitance is determined according to the length from the tip of the detection terminal to the high resistance element, and the length is specified so that the discharge energy corresponding to the amount of charge stored in the floating capacitance is less than the reference discharge energy.

In an eleventh aspect of the present invention, the length from the tip of the detection terminal to the high resistance element is maintained at a length such that the stray capacitance, which is determined according to the length, is 0.1 pF to 5 pF, and the high resistance element is set to 100 MΩ to 600 MΩ.

In a twelfth aspect of the present invention, the length from the tip of the detection terminal to the high resistance element is maintained at a length such that the stray capacitance is 3 pF, and the high resistance element is set to 100 MΩ.

The capacitance measuring device of this invention makes it easy to grasp the electrical characteristics of the object to be measured, such as capacitance and leakage resistance, simply by contacting the detection terminals with the object to be measured. Therefore, measures such as explosion prevention can be taken in advance according to the object to be measured.

According to the third and fourth aspects of the present invention, the size of the capacitor provided in the measuring device can be appropriately set in accordance with the object to be measured, thereby improving the measurement accuracy of the electrical characteristic value.

According to the fifth aspect of the present invention, the measurement object can be neutralized before measuring the electrical characteristic value of the measurement object, and the influence of the charge on the measurement object can be eliminated.

According to the sixth aspect of the present invention, the stray capacitance on the side of the detection terminal facing the measurement object can be set small, and even if a discharge occurs between the measurement object and the detection terminal, the discharge energy at that time can be kept small, thereby preventing the discharge between the measurement object and the detection terminal from causing an ignition.

According to the seventh and eighth aspects of the present invention, the static elimination of the measurement object and the measurement of the electrical characteristic value can be carried out in a series of operations.

According to the ninth aspect of the present invention, it is possible to automatically switch between charging the capacitor and measuring the electrical characteristics.

According to the tenth, eleventh and twelfth aspects of the invention, even if a discharge occurs between the charged measurement object and the detection terminal, the discharge can be prevented from causing an ignition.

FIG. 1 is a cross-sectional view of an electrical characteristic measuring apparatus according to a first embodiment. FIG. 2 is a circuit diagram of the electrical characteristic measuring apparatus of the first embodiment. FIG. 3 is a graph showing the potential of a capacitor detected by the voltage detection means of the first embodiment, and shows an example in which the measurement target is not grounded. FIG. 4 is a graph showing the potential of a capacitor detected by the voltage detection means of the second embodiment, and shows an example in which charge leaks from the measurement target.

[First embodiment]
1 and 2 includes a grounded casing A, with the tip of a detection terminal 1 protruding from an opening of the casing A. The detection terminal 1 is connected to a conductive rod 3 via a high resistance element 2, and the conductive rod 3 is covered with an insulator 4. Furthermore, a plate-shaped switching element 5 is fixed to the end of the conductive rod 3, i.e., the end opposite the detection terminal 1.
The detection terminal 1, the high resistance element 2 and the conductive rod 3 constructed as described above are each capable of moving integrally in the axial direction.

Furthermore, a plate-shaped grounding element 6 is fixed to the casing A, and this grounding element 6 is constantly grounded via the casing A. The conductive rod 3 integral with the insulator 4 penetrates this grounding element 6 and protrudes to the opposite side to the detection terminal 1, and the switching element 5 is fixed to the protruding end, so that the conductive rod 3 and the switching element 5 are electrically connected.
A spring receiving plate 7 made of an insulating material is fixed inside the casing A so as to face the grounding element 6, and a spring member 8 is interposed between this 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 ground element 6, and the detection terminal 1 is electrically connected to the ground side via the switching element 5 and the ground element 6.
A measurement power supply circuit 9 having a capacitor C as its main element is provided on the opposite side of the spring support plate 7 from the ground element 6, and a conductor connecting element 10 is provided which is electrically connected to the measurement power supply circuit 9. The tip of the conductor connecting element 10 faces the switching element 5 in contact with the ground element 6 with a gap therebetween.

As configured as above, the switching element 5 is normally in contact with the grounding element 6 due to the spring force of the spring member 8, and the detection terminal 1 is electrically connected to the ground side. Therefore, when the detection terminal 1 is brought into contact with the object to be measured 11 shown in the figure, the object to be measured 11 is connected to the ground side and static electricity is removed.

If the detection terminal 1 is pressed even harder against the measurement target 11 from the above state, the switching element 5, which moves together with the detection terminal 1, moves against the spring force of the spring member 8 and is disconnected from the ground element 6. The switching element 5 also comes into contact with the conductor connecting element 10, connecting the detection terminal 1 to the measurement power supply circuit 9.

Therefore, the process of bringing detection terminal 1 into contact with measurement object 11 to remove static electricity and the process of disconnecting detection terminal 1 from ground and connecting it to measurement power supply circuit 9 can be achieved in a series of operations.
As is apparent from the above, the switching element 5, the grounding element 6, the spring member 8 and the conductor connecting element 10 cooperate to form the switching mechanism of the present invention.

On the other hand, as shown in FIG. 2, the measurement power supply circuit 9 includes a capacitor C, which is a power supply for measurement, a voltage detection means V for detecting the voltage of the capacitor C, a DC power supply 12 for storing electricity in the capacitor C, an interlocking switch 13 for opening and closing between the power supply 12 and the capacitor C, and a manual switch 15 for opening and closing between the interlocking switch 13 and the capacitor C.

The interlocking switch 13 is interlocked with the switching element 5 via the interlocking means 14. In other words, when the switching element 5 is in contact with the grounding element 6, the interlocking switch 13 is kept on, the capacitor C is connected to the power source 12, and the capacitor C is charged.

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 is turned off, the charging of the capacitor C by the power source 12 is interrupted, and the charge stored in the capacitor C flows to the measurement target 11 via the detection terminal 1.

When the electrical characteristic measuring device described above is simply brought into contact with the detection terminal 1 to be measured 11, the switching element 5 comes into contact with the grounding element 6 due to the spring force of the spring member 8, connecting the detection terminal 1 to the ground side, and the interlocking switch 13 is turned on as shown in Figure 2 to charge the capacitor C.

When the detection terminal 1 is brought into contact with the object to be measured 11 as described above and then pressed against the object to be measured 11, the detection terminal 1 pushes the switching element 5 against the spring force of the spring member 8 via the conductive rod 3, disconnecting the switching element 5 from the ground element 6 and bringing the switching element 5 into contact with the conductor connecting element 10.

In addition, during the process in which the switching element 5 comes into contact with the conductor connecting element 10 as described above, the interlocking means 14 pushes open the interlocking switch 13, interrupting the charging of the capacitor C, and the charge stored in the capacitor C is conducted to the detection terminal 1 via the conductor connecting element 10, the switching element 5, the conductive rod 3, and the high resistance element 2. The potential Vc of the capacitor C at this time is detected by the voltage detection means V.

An arithmetic means OP is connected to the voltage detection means V, so that the potential detected by the voltage detection means V is input to the arithmetic means OP.
The calculation means OP regards the potential of the capacitor C detected by the voltage detection means V before the detection terminal 1 is brought into contact with the object to be measured 11 as an initial potential V1, and regards the potential of the capacitor C detected by the voltage detection means V after the detection terminal 1 is brought into contact with the object to be measured 11 as a post-contact potential V2.
The measurement power supply circuit 9 and the computing means OP may be integrally incorporated within the casing A, or may be provided outside the casing A.

The calculation means OP, which has grasped the initial potential V1 and the post-contact potential V2 as described above,
The following calculation formula: V2 = (Co · V1) / (Co + Cx) ... (1)
The capacitance Cx of the measurement object 11 is calculated based on the above.
In the above formula, Co is the capacitance of the capacitor C provided inside the casing A. The above formula (1) is for a circuit in which the capacitor C and the measurement object 11 are connected in parallel, and it can be seen that the capacitance Cx depends on the ratio of the initial potential V1 to the post-contact potential V2.

In addition, if the measurement object 11 is charged to a high potential while the detection terminal 1 is being brought closer to the measurement object 11, a discharge may occur between the measurement object 11 and the detection terminal 1, resulting in an ignition discharge. In order to prevent such an ignition discharge, this embodiment actively utilizes the stray capacitance SC generated on the detection terminal 1 side.

In other words, when a voltage is applied to the detection terminal 1, a stray capacitance SC is generated between the length L from the tip of the detection terminal 1 to the high resistance element 2 and the casing A facing this length L. The magnitude of this stray capacitance SC increases as the length L increases.
In this embodiment, the detection terminal 1 and the casing A are opposed to each other so that a stray capacitance SC is generated between them. However, for example, the opposite surface of the detection terminal 1 may be a floor surface or another component that maintains a ground potential.

The stray capacitance SC is determined in proportion to the length L between the detection terminal 1 and the casing A, and it is desirable to make the capacitance as small as possible.
If the capacitance of the stray capacitance SC is thus tiny, even if a discharge occurs between the tip of the detection terminal 1 and the object to be measured 11, only a current equivalent to the amount of charge stored in the stray capacitance flows between the object to be measured 11 and the detection terminal 1, so that the detection terminal 1 and the object to be measured 11 instantly become at the same potential.
Furthermore, if the stray capacitance SC is small, charging and discharging are repeated in a short time, but the current flowing due to such repeated charging and discharging is also sufficiently small, and the discharge energy is also small.

As described above, the stray capacitance SC is determined by the length L between the detection terminal 1 and the casing A, which is the stray capacitance generating means, but this length L also changes depending on the cross-sectional shape of the detection terminal 1. For example, if the opposing area is large, such as a conductor with a flat cross section or a large diameter conductor, the length can be relatively short. Also, the smaller the distance between the part that forms the stray capacitance SC and the external ground body, the larger the capacitance. In this way, the capacitance of the stray capacitance SC is not determined only by the length L, but the shorter the length L, the smaller the capacitance will be. Therefore, in this embodiment, the capacitance of the stray capacitance SC is managed by managing the length L.

The high resistance element 2 separates the floating capacitance SC portion from the conductor portion from the tip of the detection terminal 1 to the measurement power supply circuit 9, suppresses the flow of current during the discharge, and stores electricity in the floating capacitance SC. After the tip of the detection terminal 1 comes into contact with the measurement object 11, the high resistance element 2 must maintain a resistance value that allows the static electricity of the measurement object 11 to flow smoothly to the ground element 6.

For example, when the stray capacitance SC 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 that 3 pF and 100 MΩ are fully permissible.
However, the smaller the stray capacitance SC, the better. This is because the smaller the stray capacitance SC, the smaller the discharge energy during discharge. However, if the minimum ignition energy of the flammable material is large, the capacitance of the stray capacitance SC may be increased accordingly. In practice, a range of 0.1 pF to 5 pF is within the allowable limit.

The higher the resistance value of the high resistance element 2, the better in order to store the charge discharged from the measurement object 11 in the floating capacitance SC during discharge. However, there is a limit to the size of the resistance, taking into account the need to eliminate static electricity from the measurement object 11. The upper limit is about 500 to 600 MΩ, taking into account the time constant τ.

The static elimination mechanism described above brings the tip of the detection terminal 1, together with the casing A, close to the measurement object 11. If a discharge occurs between the tip of the detection terminal 1 and the measurement object 11 during this process, a current flows between them. At this time, because the resistance value of the high resistance element 2 is large, the discharge current from the measurement object 11 does not flow through the detection terminal 1 all at once, and charge is stored in the floating capacitance SC until it has the same potential as the measurement object 11. Since the floating capacitance SC has a small capacity, it is instantly fully charged, and the potential of the tip of the detection terminal 1 becomes the same as the measurement object 11.

Since the tip of the detection terminal 1 and the object to be measured 11 instantly become at the same potential, the discharge stops and the current flowing due to the discharge becomes extremely small.
Furthermore, if the potential at the stray capacitance SC becomes zero due to discharge, discharge occurs again, and discharge is repeated every time the potential of the stray capacitance becomes zero. However, since the current caused by the repeated discharges is small, it does not result in ignition discharge.

A method for measuring the capacitance, which is an electrical characteristic of the measurement target 11, using the first embodiment as described above will now be described.
In this embodiment, the measurement target 11, whose capacitance is to be measured, is electrically floating.

When the detection terminal 1 is separated from the measurement target 11, the switching element 5 is separated from the tip of the conductor connecting element 10, so the interlock switch 13 is kept on. In this case, the manual switch 15 is also kept on.
Therefore, the capacitor C is charged from the power source 12 and the capacitor C is fully charged.

The potential of the capacitor C when fully charged is detected by the voltage detection means V, and data relating to the potential is input to the calculation means OP, which grasps it as an initial potential V1.
Once the capacitor C has been charged as described above, the detection terminal 1 is brought into contact with the object to be measured 11. Even if a discharge occurs between the detection terminal 1 and the object to be measured 11 during the contact process, as the discharge energy is small as described above, there is almost no risk of a fire.

When the detection terminal 1 comes into contact with the object to be measured 11, the object to be measured 11 first connects to the ground element 6, and thus the object to be measured 11 is de-electrified. The reason for de-electrifying the object to be measured 11 in this manner is as follows. That is, if the object to be measured 11 is charged, the charge from the capacitor C is added to the charge held by the object to be measured 11, and it becomes impossible to measure the capacitance, which is an attribute of the object to be measured 11.

Once the measurement target 11 has been neutralized and its charge reduced to zero as described above, the detection terminal 1 that was in contact with the measurement target 11 is further pressed in. When the detection terminal 1 is pressed in further, the pressing force is transmitted to the switching element 5 via the conductive rod 3, and the switching element 5 is separated from the ground element 6, keeping the measurement target 11 in an electrically floating state.
When the switching element 5 is separated from the ground element 6, the switching element 5 comes into contact with the conductor connecting element 10, thereby connecting the measurement target 11 and the capacitor C together.
When the switching element 5 is separated from the grounding element 6 as described above, the interlocking means 14 moves in conjunction with the switching element 5 to turn off the interlocking switch 13.

When the interlock switch 13 is in an OFF state and the detection terminal 1 comes into contact with the object to be measured 11 , a part of the charge stored in the capacitor C flows from the detection terminal 1 to the object to be measured 11 .
In this state, the amount of charge in the object to be measured 11 saturates, and the potential of the object to be measured 11 and the potential of the capacitor C become the same potential, but the voltage detection means V detects the potential of the capacitor C at the time when they become the same potential as the post-contact potential V2 and inputs it to the calculation means OP.
The calculation means OP calculates the capacitance Cx of the measurement object 11 from the initial potential V1, the post-contact potential V2, and the capacitance Co of the capacitor C using the above-mentioned calculation formula (1).

3 is a graph showing the change over time in the potential Vc of the capacitor C detected by the voltage detection means V, with the point in time, 0 being the point on the horizontal axis showing time, when the detection terminal 1 is pressed against the measurement object 11 and connected to the capacitor C. Fig. 3 also shows an example in which the measurement object 11 maintains an electrically floating state, and the charge of the capacitor C flows into the measurement object 11, causing the potential of the capacitor C to instantaneously change from the initial potential V1 to the post-contact potential V2, after which the post-contact potential V2 is maintained approximately constant.
In this way, in the measurement device of the first embodiment, the capacitance Cx of the measurement object 11 can be calculated by detecting the initial potential V1 and the post-contact potential V2.

In the first embodiment described above, the static elimination mechanism is integrated into the device, but it is also possible to use a completely separate static elimination device to eliminate static electricity from the measurement object 11 in advance.

Ideally, the capacitance of the capacitor C is determined according to the expected capacitance of the measurement target 11 .
For example, if the capacitance of capacitor C is made extremely large despite the assumed capacitance of measurement object 11 being small, the difference between the initial potential V1 and post-contact potential V2 will become small, making it difficult to read the rate of change.
Conversely, if the assumed capacitance of the measurement target 11 is large but the capacitance of the capacitor C is small, the capacitance of the measurement target 11 cannot be detected by the capacitance of the capacitor C alone.

For the reasons mentioned above, the capacitor C may be of a variable capacitance type, or a plurality of capacitors with different capacitances may be connected together and a capacitor having an appropriate capacitance may be selected using a selection means not shown.
A display (not shown) may be connected to the computing means OP to visualize the computation results of the computing means OP.

Reference numeral 16 in the figure denotes an insulating element covering the tip of the casing A, which is made of a highly resistant material that does not easily conduct electricity, or an insulating material that does not conduct electricity.
The tip of the casing A is covered as described above in order to prevent abnormal discharge from occurring between the casing A and the object 11 to be measured.

[Second embodiment]
Next, a second embodiment for measuring the leakage resistance value of the measurement object 11 will be described.
The measurement target 11, whose leakage resistance is to be measured, is not electrically completely floating, but is capable of passing electric charge from the measurement target 11 to ground.
In the second embodiment, the calculation means OP has a function of calculating the leakage resistance value Rx of the measurement object 11, but the other configurations are the same as those of the first embodiment shown in FIGS.

Figure 4 is a graph showing an example of the potential Vc of the capacitor C detected by the voltage detection means V. In the graph of Figure 4, the zero point on the horizontal axis indicating time is the time when the measurement object 11 and the capacitor C are connected via the detection terminal 1. The potential of the capacitor C before the detection terminal 1 contacts the measurement object 11 is the initial potential V1, and the potential of the capacitor C after the detection terminal 1 contacts the measurement object 11 is the post-contact potential V2. However, in this second embodiment, the charge of the capacitor C leaks to ground via the measurement object 11, so the post-contact potential V2 exponentially decays over time.

The calculation means OP of the second embodiment also has a function of calculating the leakage resistance value Rx of the measurement target 11 from the decay time τm of the post-contact potential V2 detected by the voltage detection means V. Specifically, the calculation means OP specifies the decay time τm until the post-contact potential V2 reaches a potential V2(τm) that is 37% of the initial potential V1 (see FIG. 4), and calculates the leakage resistance value Rx from the post-contact potential V2 using the following calculation formula τm=Co·(Rc+Rx) (2).
The leakage resistance value Rx of the measurement object 11 is calculated based on the above.

In the above formula (2), Rc is the resistance value of the high resistance element 2. This formula (2) indicates the time constant of an RC circuit in which a capacitor and a resistor are connected in series, and indicates that the smaller the leakage resistance value Rx of the measurement object 11, the shorter the decay time of the potential of the capacitor C.

In the second embodiment, the procedure for measuring the leakage resistance value Rx of the measurement target 11 is substantially the same as that for measuring the capacitance Cx in the first embodiment.
That is, when the detection terminal 1 is separated from the object 11 to be measured, the manual switch 15 is turned on to allow the power source 12 to fully charge the capacitor C.

The potential of the capacitor C when fully charged is detected by the voltage detection means V and is grasped by the calculation means OP as an initial potential V1.
Thereafter, the detection terminal 1 is brought into contact with the object to be measured 11 and further pressed in to connect the capacitor C and the detection terminal 1 .
When the capacitor C is connected to the detection terminal in contact with the object to be measured 11, the charge stored in the capacitor C flows to the object to be measured 11, and the voltage detection means V detects the post-contact potential V2 of the capacitor C and inputs the data to the calculation means OP.

In this second embodiment, the charge from the capacitor C leaks to ground through the measurement target 11, so the post-contact potential V2 decays along with the charge of the capacitor C. When the post-contact potential V2 decaying in this way is input to the calculation means OP, the calculation means OP detects the decay time τm from the post-contact potential V2. The calculation means OP may measure the time it takes for the post-contact potential V2 input from the voltage detection means V to reach a potential V2 (τm) that is 37% of the initial potential V1 to determine the decay time τm, or may calculate an approximation of the decay curve from the change in the post-contact potential V2 input from the voltage detection means V to determine the decay time τm by calculation, even if the post-contact potential V2 does not actually decay to the potential V2 (τm).

The calculation means OP calculates the leakage resistance value Rx of the measurement object 11 based on the decay time τm and the above-mentioned calculation formula (2).
By measuring the leakage resistance value Rx of the measurement object 11 in this manner, it is possible to grasp the grounding condition of the measurement object and the ease of grounding.
If the measurement object 11 is in an electrically floating state, the post-contact potential V2 is hardly attenuated as shown in FIG. 3, so it is almost impossible to actually measure the decay time τm. However, it can be confirmed that the leakage resistance value Rx is sufficiently high.
Also in this second embodiment, even if the measurement object 11 is charged before measurement and a discharge occurs between the detection terminal 1 and the measurement object 11 when the detection terminal 1 is brought close, the discharge energy can be reduced as in the first embodiment described above, so there is almost no risk of a fire accident.

The above first and second embodiments each describe the case where the capacitance Cx and leakage resistance value Rx of the measurement object 11 are measured, but the calculation means OP may also have a function for calculating both the capacitance Cx and the leakage resistance value Rx at the same time, so that the measurer can select the function of the calculation means OP depending on which electrical characteristic value is to be measured.

In addition, it is preferable that the measurement device for measuring the leakage resistance value Rx does not include the high resistance element 2 or does not set the resistance value Rc of the high resistance element 2 too large. This is because, in the above arithmetic formula (2), if the resistance value Rc of the high resistance element 2 is too large compared to the leakage resistance value Rx of the measurement target 11, the effect of the resistance value Rc on the decay time τm becomes large, and there is a possibility that the leakage resistance value Rx cannot be detected accurately.
Furthermore, when discharging the object to be measured 11, this is done via the high resistance element 2, and when measuring the resistance value, the high resistance element 2 is avoided and the detection terminal 1 is configured to be directly connected to the capacitor C, thereby eliminating the effect of the resistance value Rc.

It is useful for measuring the capacitance and leakage resistance of objects to prevent fire accidents in dangerous locations where flammable solvents or powders are handled.

1...detection terminal, 2...high resistance element, 5...switching element, 6...grounding element, 8...spring member, 10...conductor connecting element, 11...measurement object, 12...power source, L...length, SC...stray capacitance, C...capacitor, V...voltage detection means, 13...interlocking switch, 14...interlocking means, Vc...potential of capacitor C, SC...stray capacitance, OP...calculation means

Claims (12)

A detection terminal for contacting the object to be measured;
A capacitor connected to the detection terminal;
a voltage detection means for detecting the potential of the capacitor;
A calculation means for calculating the potential detected by the voltage detection means,
The detection terminal is brought into contact with the object to be measured,
The calculation means is
An electrical characteristic measuring device which defines the potential of the capacitor detected by the voltage detection means before the detection terminal is brought into contact with the object to be measured as an initial potential, and defines the potential of the capacitor detected by the voltage detection means after the detection terminal is brought into contact with the object to be measured as a post-contact potential, and calculates the capacitance of the object to be measured based on the ratio between the initial potential and the post-contact potential. A detection terminal for contacting the object to be measured;
A capacitor connected to the detection terminal;
a voltage detection means for detecting the potential of the capacitor;
A calculation means for calculating the potential detected by the voltage detection means;
Equipped with
The detection terminal is brought into contact with the object to be measured,
The calculation means is
a potential of the capacitor detected by the voltage detection means before the detection terminal is brought into contact with the object to be measured is defined as an initial potential, and a potential of the capacitor detected by the voltage detection means after the detection terminal is brought into contact with the object to be measured is defined as a post-contact potential,
The electrical characteristic measuring device calculates a leakage resistance value of the measurement object based on the decay time of the post-contact potential . 3. An electrical characteristic measuring apparatus according to claim 1, wherein said capacitor is of a variable capacitance type . 4. The electrical characteristic measuring device according to claim 1 , further comprising a selection means for connecting a plurality of capacitors having different capacitances in parallel and selecting one of the capacitors as the capacitor . On the one hand, it is equipped with a grounding element that always maintains a grounded state,
An electrical characteristic measuring device as described in any one of claims 1 to 4, wherein the detection terminal is normally connected to the grounding element, and when the detection terminal is pressed against the object to be measured and a pressing force acts on the detection terminal, a switching mechanism is provided which disconnects the detection terminal from the grounding element and connects the detection terminal to the capacitor . A high resistance element is connected to the detection terminal.
6. The electrical characteristic measuring device according to claim 5 , wherein the detection terminal is connected to the ground element or the capacitor via the high resistance element . The switching mechanism is
a switching element that moves integrally with the detection terminal and is electrically connected to the detection terminal;
The above-mentioned grounding element that is always kept in a grounded state;
a spring member that applies a spring force to the switching element and brings the switching element into contact with the ground element under the action of the spring force;
Equipped with
7. An electrical characteristic measuring apparatus according to claim 5, wherein normally, the switching element is brought into contact with a grounding element by the spring force of the spring member, thereby grounding the detection terminal . The switching mechanism is
a switching element that moves integrally with the detection terminal in the axial direction of the detection terminal;
a conductor coupling element having one end spaced from said switching element and another end electrically connected to said capacitor;
8. The electrical characteristic measuring device according to claim 5, wherein when the switching element moves by the distance against the spring force of the spring member, the switching element and the capacitor are connected via the conductor connecting element . an interlock switch provided between the capacitor and a power source for charging the capacitor;
and an interlocking means for interlocking the interlocking switch with the switching element,
9. An electrical characteristic measuring device as described in claim 7 or 8, wherein the interlocking means closes the interlocking switch when the switching element is in contact with the grounding element and is disconnected from the capacitor, and the interlocking means opens the interlocking switch when the switching element is disconnected from the grounding element and is electrically connected to the capacitor . Based on the minimum ignition energy of the combustible substance in the atmosphere in which the measurement object exists, a reference discharge energy is specified that is less than the ignition energy.
A stray capacitance is generated, the capacitance of which is determined according to the length from the tip of the detection terminal to the high resistance element,
7. The electrical characteristic measuring apparatus according to claim 6 , wherein the length is specified so that a discharge energy corresponding to an amount of charge stored in the stray capacitance is equal to or less than the reference discharge energy . An electrical characteristic measuring device as described in claim 10, wherein the length from the tip of the detection terminal to the high resistance element is maintained at a length such that the stray capacitance, determined according to the length, is 0.1 pF to 5 pF, and the high resistance element is 100 MΩ to 600 MΩ . 11. The electrical characteristic measuring device according to claim 10, wherein a length from the tip of the detection terminal to the high resistance element is maintained such that the stray capacitance is 3 pF, and the high resistance element is set to 100 MΩ .

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