JP2015175596A - Impedance measuring method, and impedance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of simply setting an appropriate measurement frequency when the change of the electrostatic capacitance of a capacitor is detected.SOLUTION: An impedance measuring method for detecting the change of the electrostatic capacitance of a capacitor, comprises: a first step S1 in which is calculated data that shows relationship between a measurement frequency and a loss coefficient in the impedance measurement by simulation using a parallel equivalent circuit model based on a reference value of the electrostatic capacitance of the capacitor and based on the insulation resistance between the electrodes of the capacitor; a second step S2 in which the measurement frequency is decided in a range between the first frequency and the second frequency higher than the first frequency based on the data showing the relationship between the measurement frequency and the loss coefficient; a third step S3 in which impedance measurement of the capacitor is performed using the AC voltage of the measurement frequency decided in the second step; and a fourth step S4 in which the measurement value of the electrostatic capacitance of the capacitor is calculated on the basis of the measurement result of the impedance measurement.

Description

  The present invention relates to an impedance measurement method and an impedance measurement device.

  When measuring strain or the like of piping, a capacitance type sensor that detects a change in physical quantity due to the strain as a change in capacitance of a capacitor is used. When detecting a change in the capacitance of the capacitor, impedance measurement using the IV method or the automatic balanced bridge method is used (see Patent Document 1).

JP 2007-033286 A

  In impedance measurement, when accurately detecting changes in the capacitance of a capacitor, it is necessary to take into account parasitic components such as parasitic resistance due to loss of the capacitor dielectric and electrodes, parasitic resistance due to lead wires, and parasitic inductance. . Therefore, the influence of these parasitic components is reduced by appropriately setting the frequency of the AC signal applied to the capacitor (hereinafter referred to as “measurement frequency”).

  Specifically, as a sample check, measure the impedance of the capacitor at an appropriate measurement frequency, and refer to the loss coefficient D value (ratio of resistance component to reactance component) calculated from the impedance and representing the effect of parasitic components. Therefore, the current situation is that a method for determining whether or not the measurement frequency is an appropriate value is used.

  However, the parasitic component and capacitance of the capacitor may change greatly depending on the aging and measurement environment, and the work of determining whether or not the measurement frequency is appropriate is complicated.

  Accordingly, an object of the present invention is to propose an impedance measurement method and an impedance measurement device that can easily set an appropriate measurement frequency when performing impedance measurement for detecting a change in capacitance of a capacitor. To do.

  The main present invention for solving the above-mentioned problem is an impedance measurement method for detecting a change in capacitance of a capacitor, wherein the parallel measurement is based on a reference value of the capacitance of the capacitor and an insulation resistance between electrodes of the capacitor. A first step of calculating data indicating the relationship between the measurement frequency and the loss factor in the impedance measurement by simulation using an equivalent circuit model, and the first frequency based on the data indicating the relationship between the measurement frequency and the loss factor The second step of determining the measurement frequency within a range between the second frequency higher than the first frequency and the impedance measurement of the capacitor using the AC voltage of the measurement frequency determined in the second step Third step and a fourth step of calculating a measured value of the capacitance of the capacitor based on the measurement result of the impedance measurement Is the impedance measurement method comprising.

  Other features of the present invention will become apparent from the accompanying drawings and the description of this specification.

  According to the present invention, it is possible to easily set an appropriate measurement frequency when performing impedance measurement.

It is a figure showing an equivalent circuit model of a capacitor. It is a figure showing an equivalent circuit model of a capacitor. It is a figure which shows the internal structure of the measuring apparatus in 1st Embodiment of this invention. It is a figure which shows the internal structure of the measuring apparatus in 1st Embodiment of this invention. It is a figure which shows the measurement flow in 1st Embodiment of this invention. It is a figure explaining a loss coefficient. It is a figure which shows the relationship between the measurement frequency and loss factor in 1st Embodiment of this invention. It is a figure which shows the to-be-measured object in 1st Embodiment of this invention. It is a figure which shows the to-be-measured object in 1st Embodiment of this invention. It is a figure which shows the measurement flow in 2nd Embodiment of this invention. It is a figure which shows the internal structure of the measuring apparatus in 2nd Embodiment of this invention. It is a figure explaining the current characteristic when a DC voltage is applied to a capacitor.

  At least the following matters will become apparent from the description of this specification and the accompanying drawings.

<First Embodiment>
In the present embodiment, an aspect will be described in which impedance measurement is performed using a measurement device described later, a change in the capacitance of the capacitor is detected based on the measurement result, and the strain of the pipe is calculated.

  First, the parallel equivalent circuit model used when calculating the measured value of the capacitance of the capacitor in this embodiment will be described.

  As described above, a capacitor has parasitic components such as parasitic resistance due to loss of the dielectric and electrodes of the capacitor, parasitic resistance due to lead wires, and parasitic inductance, and the equivalent circuit model of the capacitor is generally equivalent. It is represented by an equivalent circuit model shown in FIG. 1B having a parallel resistance Rp, an equivalent series resistance ESR, and an equivalent series inductance ESL.

  Therefore, the accurate capacitance C of the capacitor is a value obtained by distinguishing these parasitic components from the measurement result of the impedance measurement. However, it is difficult to accurately distinguish the capacitance C of the capacitor from the equivalent parallel resistance Rp, the equivalent series resistance ESR, and the equivalent series inductance ESL.

  On the other hand, since the influence of the equivalent parallel resistance Rp is considerably larger than the influence of the equivalent series resistance ESR (such as the lead resistance) and the equivalent series inductance ESL, the capacitor having a small capacitance of 1 nF or less has the equivalent series resistance ESR, and The equivalent series inductance ESL can be ignored.

  Therefore, in this embodiment, a parallel equivalent circuit model including only the equivalent parallel resistance Rp and the capacitance C of the capacitor shown in FIG. 1A is used.

=== Hardware Configuration of Measuring Apparatus ===
FIG. 2 shows an example of the internal configuration of the measuring apparatus 1.

  The measurement apparatus 1 includes a control unit 100, a storage unit 200, a display unit 300, an impedance measurement unit 400, and an input unit 500.

  The control unit 100 is a CPU, and is connected to the storage unit 200, the display unit 300, the impedance measurement unit 400, and the input unit 500 via the bus 600. Based on the computer program stored in the storage unit 200, the control unit 100 performs data communication with the storage unit 200, the display unit 300, the impedance measurement unit 400, and the input unit 500 and controls their operations.

Although details will be described later, the control unit 100 measures and measures the loss coefficient D value based on the insulation resistance Rp ′ between the electrodes of the capacitor and the reference value C _{0 of the} capacitance of the capacitor based on the computer program. A first calculator that calculates data relating to frequency, and a parallel equivalent circuit model applied to a measurement result of the impedance of the capacitor measured by the impedance measuring unit 400 to calculate a measured value of the capacitance of the capacitor. 2 has a function of a third calculator that calculates the strain of the object to be measured from the measured value of the capacitance of the capacitor calculated by the second calculator.

  The storage unit 200 includes a volatile memory (for example, RAM) and a nonvolatile memory (for example, a flash memory or a magnetic disk). The storage unit 200 stores a computer program for controlling the measurement apparatus 1 and control data of the impedance measurement unit 400 corresponding to the measurement conditions. Further, the storage unit 200 stores a calculation model for calculating the distortion of the device under test from the measurement result of the capacitor impedance measurement described later.

  The display unit 300 is, for example, a liquid crystal display that displays various types of information, and displays distortion of the measurement object described later.

  The impedance measurement unit 400 includes, for example, an oscillator 410, a current-voltage conversion unit 420, and a vector ratio detection unit 430, and measures the impedance of the capacitor based on the automatic balanced bridge method.

The input unit 500 is, for example, a switch or a touch panel, and receives an operation instruction from the user of the measurement apparatus 100. The user can, for example, measure the impedance in the measurement apparatus 100 via the input unit 500, the insulation resistance Rp ′ between the electrodes of the capacitor used for the simulation described later, and the reference value of the capacitance of the capacitor. C ₀ can be entered.

=== Configuration of Impedance Measurement Unit ===
The impedance measurement unit 400 according to the present embodiment performs impedance measurement by an automatic balanced bridge method.

  FIG. 3 shows an example of the configuration of the impedance measurement unit 400 of the present embodiment.

  The impedance measurement unit 400 includes an oscillator 410, a current-voltage conversion unit 420, and a vector ratio detection unit 430, and measures the impedance of the capacitor M connected to the impedance measurement unit 400.

  In the present embodiment, the capacitor M is a capacitor having a small capacitance, and the measurement target is 1 nF or less as described above. The capacitor M (indicated as “DUT”) is connected to the impedance measuring unit 400 via four terminals (Lc terminal, Lp terminal, Hc terminal, Hp terminal).

  The oscillator 410 is composed of a frequency synthesizer, and generates an AC voltage applied to the capacitor M. In the present embodiment, the AC voltage is a sine wave signal having a measurement frequency determined within a range of an appropriate measurement frequency calculated by simulation described later.

  The current-voltage converter 420 includes a reference resistor 421 and a zero detector 422, converts the current flowing through the capacitor M into a voltage signal, and outputs the voltage signal to the vector ratio detector 430. Specifically, the zero detector 422 of the current-voltage converter 420 flows through the reference resistor 421 and the capacitor M so that the current flowing into the negative side input terminal of the zero detector 422 becomes zero. The current is balanced. As a result, the current flowing through the capacitor M is passed through the reference resistor 421 to convert the current into a voltage signal.

  The vector ratio detection unit 430 measures the voltage V1 applied to the capacitor M and the voltage V2 voltage-converted by the current-voltage conversion unit 420, and calculates the impedance of the capacitor M. Specifically, the vector ratio detection unit 430 includes a vector voltmeter 431. The vector ratio detection unit 430 measures the magnitude of the vector of the voltage V1 applied to the capacitor M and also measures the magnitude of the vector of the voltage V2 applied to the reference resistor 421. From the vector magnitude ratio and the resistance R, the impedance Z of the capacitor M is calculated by Equation 1.

  Then, the vector ratio detection unit 430 calculates the resistance component and reactance component of the impedance Z of the capacitor M from the phase difference between the voltage V1 (reference signal of the oscillator 410) and the voltage V2 (signal output from the current-voltage conversion unit 420). calculate.

一方、本実施形態では、コンデンサＭは、並列等価回路モデルを適用したコンデンサであるから、インピーダンスは、コンデンサＭの静電容量Ｃと、等価並列抵抗Ｒｐにより式２により表すことができる。

On the other hand, in the present embodiment, the capacitor M is a capacitor to which a parallel equivalent circuit model is applied. Therefore, the impedance can be expressed by Equation 2 using the capacitance C of the capacitor M and the equivalent parallel resistance Rp.

（Ｚはインピーダンス（Ω）、Ｃは静電容量（Ｆ）、Ｒｐは等価並列抵抗（Ω）、ωは角周波数（ｒａｄ／ｓ）を表す）
これより、本実施形態の測定装置１は、インピーダンス測定の測定結果から、式１、式２に基づいて、コンデンサＭの静電容量の測定値を算出する。

(Z represents impedance (Ω), C represents capacitance (F), Rp represents equivalent parallel resistance (Ω), and ω represents angular frequency (rad / s))
From this, the measuring apparatus 1 of this embodiment calculates the measured value of the capacitance of the capacitor M based on the formulas 1 and 2 from the measurement result of the impedance measurement.

  The measuring apparatus 1 of the present embodiment calculates the measured value of the capacitance of the capacitor M with the above configuration.

=== About measurement flow ===
Next, a measurement flow when measuring the capacitance of the capacitor M (detecting a change) using the measurement apparatus 1 of the present embodiment will be described.

  FIG. 4 shows a measurement flow in the present embodiment.

S1 calculates data indicating the relationship between the measurement frequency f and the loss factor D value by simulation using a parallel equivalent circuit model based on the reference value C _{0 of the} capacitance of the capacitor M and the insulation resistance Rp ′ between the electrodes. It is a process to do.

  In order to accurately measure the capacitance of the capacitor, it is necessary to determine the measurement frequency so as to reduce the influence of the parasitic component (resistance component) as described above. Therefore, in the present embodiment, an appropriate measurement frequency range is calculated by calculating data indicating the relationship between the measurement frequency f and the loss coefficient D value by simulation.

  The loss factor D value is represented by the ratio of the resistance component to the reactance component of the impedance as shown in FIG. 5 and Equation 3, and the smaller the D value, the more accurate the capacitance is measured without the influence of the parasitic component. I can understand what is being done.

ここで、１ｎＦ以下の静電容量の小さなコンデンサにおいては、等価並列抵抗Ｒｐは、コンデンサの電極間の絶縁抵抗とみなすことができる。そのため、等価並列抵抗Ｒｐとして、コンデンサＭの設計値より予測される電極間の絶縁抵抗Ｒｐ’を用いることができる。また、コンデンサＭの静電容量Ｃについても、コンデンサＭの設計値より予測される基準値Ｃ₀を用いることができる。

Here, in a capacitor having a small capacitance of 1 nF or less, the equivalent parallel resistance Rp can be regarded as an insulation resistance between the electrodes of the capacitor. Therefore, the insulation resistance Rp ′ between the electrodes predicted from the design value of the capacitor M can be used as the equivalent parallel resistance Rp. Further, the reference value C ₀ predicted from the design value of the capacitor M can also be used for the capacitance C of the capacitor M.

  In the parallel equivalent circuit model, the impedance Z of the capacitor can be expressed as shown in Equation 2.

Therefore, in this step, using the reference value C _{0 of the} capacitance of the capacitor M and the insulation resistance Rp ′ between the electrodes, which is input to the input unit 500 by the user of the measuring apparatus 1, The data indicating the relationship between the measurement frequency f and the loss factor D value is calculated by simulation.

図６に、シミュレーションにより算出した測定周波数ｆと損失係数Ｄ値の関係を示すグラフの一例を示す。図６に示すデータは、静電容量の基準値Ｃ₀が１．５ｐＦ、電極間の絶縁抵抗Ｒｐ’が１００ＭΩのコンデンサの損失係数Ｄ値を、所定の測定周波数ｆごとに、式４を用いて算出したデータとなっている。

FIG. 6 shows an example of a graph showing the relationship between the measurement frequency f calculated by simulation and the loss factor D value. In the data shown in FIG. 6, the loss coefficient D value of a capacitor having a capacitance reference value C ₀ of 1.5 pF and an insulation resistance Rp ′ between the electrodes of 100 MΩ is expressed by Equation 4 for each predetermined measurement frequency f. This is the calculated data.

The reference value C _{0 of the} capacitance and the insulation resistance Rp ′ between the electrodes predicted from the design value of the capacitor M used in this embodiment are the design value of the capacitor M (electrical resistivity of the dielectric). , The distance between the electrodes, the surface area of the portion where the electrodes face each other, and the relative dielectric constant of the dielectric) are predicted values based on Equations 5 and 6.

（ρは電極間に挟まれる誘電体の電気抵抗率（Ω・ｍ）、ｄは電極間距離（ｍ）、Ｓはコンデンサの電極が対向する部分の表面積（ｍ²）を表す）

(Ρ is the electrical resistivity (Ω · m) of the dielectric sandwiched between the electrodes, d is the distance between the electrodes (m), and S is the surface area (m ² ) of the part where the electrodes of the capacitor face each other)

（Ｃ₀は静電容量（Ｆ）、ε_rは電極間に挟まれる誘電体の比誘電率、ε₀は真空の誘電率（Ｆ／ｍ）、ｄは電極間距離（ｍ）、Ｓは電極が対向する部分の表面積（ｍ²）を表す）
尚、コンデンサの静電容量の基準値Ｃ₀は、上記のコンデンサの設計値（電極間の膜厚、電極が対向する部分の表面積、誘電体材料の比誘電率）より予測される値のほか、コンデンサの使用開始時の静電容量の測定値や、前回測定したときの静電容量の測定値を用いることができる。

(C ₀ is the capacitance (F), ε _r is the relative permittivity of the dielectric sandwiched between the electrodes, ε ₀ is the vacuum permittivity (F / m), d is the distance between electrodes (m), and S is The surface area (m ² ) of the part where the electrode faces)
The reference value C ₀ of the capacitance of the capacitor is a value predicted from the above-described capacitor design values (film thickness between electrodes, surface area of the portion where the electrodes face each other, dielectric constant of dielectric material). The measured value of the capacitance at the start of use of the capacitor or the measured value of the capacitance when measured last time can be used.

  In addition, in this step, if an appropriate range of the measurement frequency f can be calculated, other values corresponding to the loss coefficient D value are calculated instead of calculating data indicating the relationship between the measurement frequency f and the loss coefficient D value. It may be calculated. For example, instead of the ratio of the resistance component to the reactance component, the ratio of the reactance component to the resistance component may be calculated.

  Moreover, this process may calculate the measurement frequency f when the loss coefficient D value becomes 0.1.

S2 is a step based on the data indicating the relationship between the loss factor D value calculated measurement frequency f in S1, to determine a measurement frequency f _d.

  In the present embodiment, when a measurement frequency that is 0.1 or less is used as the reference value of the loss coefficient D value, it is determined that the influence of the parasitic component (resistance component) is small. Thus, in this step, based on the simulation result, the measurement frequency at which the loss coefficient D value is 0.1 or less is determined as the appropriate measurement frequency range. In the example of FIG. 6, a measurement frequency of 10 kHz or more is appropriate.

  At this time, the loss factor D value calculated by the simulation is calculated as a smaller value as the measurement frequency is increased. However, in reality, if the measurement frequency is increased too much, the influence of the parasitic inductance increases and It becomes impossible to accurately measure the electric capacity, that is, the measured value of the loss coefficient D value also increases.

Therefore, in the present embodiment, the measurement frequency f _d is appropriately determined within a range in which the measurement frequency at which the loss coefficient D value is 0.1 is the lower limit and the measurement frequency at which the loss coefficient D value is 0.001 is the upper limit. Here, the lower limit of the measurement frequency at which the loss coefficient D value is 0.1 or less is that, as described above, the influence of the parasitic component of the equivalent parallel resistance at the time of impedance measurement becomes large. The reason why the upper limit is the measurement frequency at which the loss coefficient D value is approximately 0.001 is that, when the frequency is exceeded, the influence of parasitic inductance tends to increase even with a capacitor having a small capacitance.

  In the case of a capacitor having a small capacitance of 1 nF or less, the influence of the parasitic inductance is the most at the measurement frequency where the loss coefficient D value is approximately 0.05 and below the measurement frequency where the loss coefficient D value is approximately 0.001. Since there is a tendency that it is difficult to receive, the range of the measurement frequency may be an optimum range.

S3 is using the measurement frequency f _d which is determined in S2, the impedance measuring unit 400, a step of measuring the impedance.

This process is specifically set to measure the frequency f _d which determines the measurement frequency of the oscillator 410 in S2, the impedance measuring unit 400, perform an in-peen dance measurement. Then, as a measurement result of the impedance measurement, an impedance and a phase difference between the voltage V1 (reference signal of the oscillator 410) and the voltage V2 (signal output from the current-voltage conversion unit 420) are measured.

  S4 is a step of calculating a measured value of the capacitance of the capacitor by using Equations 1 and 2 based on the measurement result of the impedance measurement of S3.

  As described above, since the capacitor M is a capacitor to which a parallel equivalent circuit model is applied, the impedance can be expressed by Equation 2 including the capacitance C of the capacitor and the equivalent parallel resistance Rp. Therefore, based on the impedance, which is the measurement result of the impedance measurement in S3, and the phase difference between the voltage V1 (reference signal of the oscillator 410) and the voltage V2 (signal output from the current-voltage conversion unit 420), Expressions 1 and 2 Thus, the measured value of the capacitance of the capacitor M can be calculated.

  S5 is a step of calculating the strain of the device under test based on the measured value of the capacitance of the capacitor M calculated in S4.

  Specifically, this step is a step of calculating the distortion by calculating the change amount of the distance between the electrodes of the capacitor M or the change amount of the opposing area based on the measured value of the capacitance of the capacitor M. An example of a distortion calculation method will be described later.

  Then, the measuring apparatus 1 causes the display unit 300 to display the distortion calculated in this step. The display mode at this time is, for example, displayed as text data in association with the measurement date and distortion.

=== About the structure of the object to be measured ===
Next, the configuration of the object to be measured in this embodiment will be described.

  7A and 7B show an example of the configuration of the device under test.

  7A is a perspective view of the object to be measured, and FIG. 7B is a cross-sectional view of the object to be measured (an XZ plane cut surface passing through the centers of the first device M800 and the second device M200 described later).

  An object to be measured according to the present embodiment includes a pipe P, and a first apparatus M800 and a second apparatus M200 installed on the surface of the pipe P. The first device M800 and the second device M200 use the cylindrical electrode M72 included in the first device M800 and the rod-shaped electrode M32 included in the second device M200 as electrodes, and the atmosphere between the cylindrical electrode M72 and the rod-shaped electrode M32. A capacitor M as a dielectric is formed.

  The pipe P is a pipe provided in a thermal power plant and used for a boiler, a turbine, and the like, and is exposed to a high temperature environment and is likely to be distorted. When the pipe P is distorted in the X direction, the distance between the first device M800 (tubular electrode M72) and the second device M200 (bar electrode M32) installed (fixed) on the surface of the pipe P changes, and the capacitor M Therefore, the strain is measured by detecting the change in the capacitance. 7A and 7B, the Z axis is an axis along the height direction (vertical direction) where the first device M800 and the second device M200 are installed, and the X axis is the longitudinal direction of the pipe P. The Y axis indicates an axis orthogonal to the X axis and the Z axis. In the following description, the “X direction”, the “Y direction”, and the “Z direction” are simply expressed, the direction indicated by the arrow is the + direction, and the direction opposite to the arrow is the − direction.

  Hereinafter, specific configurations of the first device M800 and the second device M200 will be described.

= First device =
The first device M800 includes a first attachment device M8 and a first electrode body M7.

  The 1st attachment apparatus M8 is an apparatus for attaching the 1st electrode body M7 with respect to the piping P, and is being fixed to the piping P via the leg M85 arrange | positioned at the four corners of a bottom face (-Z).

  Specifically, the first mounting device M8 includes a first metal member M81 having a cylindrical hole in the X direction, and a first insulating member fixed to the inner peripheral surface of the cylindrical hole of the first metal member M81. The box is composed of M82 and M83, and the first electrode body M7 is inserted and arranged on the inner peripheral side of the first insulating members M82 and M83.

The first metal member M81 has a slit M8B extending in the X direction on the side surface (side surface along the longitudinal direction) on the −Y direction side. Further, the first metal member M81 has a screw hole extending in the −Z direction from the top surface to the vicinity of the bottom surface through the slit M8B portion on the side where the slit M8B on the top surface is provided (not shown). ). Then, a screw is inserted into the screw hole, the width in the Z direction of the slit M8B is adjusted, the first metal member M81 is deformed, and the first electrode body M7 is fixed to the first mounting device M8. It is possible.
The first insulating members M82 and M83 are insulating members such as ceramics for electrically insulating the first electrode body M7 from the pipe P. And the 1st insulating member M82 is along the upper side of the inner peripheral surface of the cylindrical hole of the first metal member M81, and the first insulating member M83 is the inner peripheral surface of the cylindrical hole of the first metal member M81. A pair is fixed to the inner peripheral surface of the first metal member M81 along the lower side.

  Further, as described above, the first electrode body M7 is disposed on the inner peripheral side (the inner peripheral side of the cylindrical hole) of the first insulating members M82 and M83, and from the outer side to the inner side of the first mounting device M8, A first case M71, a first support member M73, and a cylindrical electrode M72 are arranged. That is, the first case M71 and the first support member M73 are interposed between the outer peripheral surface of the internal cylindrical electrode M72 and the inner peripheral surfaces of the first insulating members M82 and M83.

  The first case M71 is a metal casing that houses the insulating first support member M73 and the cylindrical electrode M72 and has a hollow structure inside. The first case M71 has a first opening M74 penetrating the side surface on the side surface on the + X side (the side surface opposite to the side surface facing the second device). Then, one end of the first coaxial cable L is inserted from the first opening M74 and connected to the end of the cylindrical electrode M72 on the + X side (opposite to the end facing the second device). The first case M71 has a second opening M75 having a diameter larger than the diameter of the rod-like electrode M32 penetrating the side surface on the side surface on the −X side (the side surface facing the second device). Then, one end of the rod-like electrode M32 is inserted into the second opening M75 until it reaches the inside of the cylindrical electrode M72, and the rod-like electrode M32 can advance and retreat along the X axis.

  The first support member M73 is made of an insulating member, and supports the cylindrical electrode M72 inside the first case M71 so that the cylindrical electrode M72 does not contact the first case M71. The first support member M73 also has an opening (not shown) penetrating the first case M71 and a side surface on the + X side (a side surface opposite to the side surface facing the second device) penetrating the side surface. One end of the cable L is inserted.

  The cylindrical electrode M72 is a metal member for forming a capacitor together with the rod-like electrode M32. The cylindrical electrode M72 has a cylindrical shape extending along the X direction of the pipe P and exhibiting a hollow structure having an opening in the −X direction (side facing the second device). The rod-shaped electrode M32 is inserted from the opening in the −X direction of the cylindrical electrode M72, and a capacitor M using air as a dielectric is formed at a portion where the cylindrical electrode M72 and the rod-shaped electrode M32 face each other. That is, the capacitor M is placed on the surface of the pipe P so that the capacitor M can move independently of the first electrode M800 to a position facing the first device M800 fixed to the surface of the pipe P and the first device M800. It is formed by the fixed second electrode M200.

= Second device =
The second device M200 includes a second attachment device M2 and a second electrode body M3.

  The second attachment device M2 is a device for attaching the second electrode body M3 to the pipe P, and is fixed to the pipe P via legs M25 arranged at the four corners of the bottom surface (−Z).

  The second mounting device M2 has the same configuration as the first mounting device M8.

  Specifically, the second mounting device M2 includes a second metal member M21 having a cylindrical hole in the X direction, and a second insulating member fixed to the inner peripheral surface of the cylindrical hole of the second metal member M21. It is a box composed of M22 and M23, and is configured such that the second electrode body M3 is inserted and arranged on the inner peripheral side of the second insulating members M22 and M23.

  The second electrode body M3 is arranged on the inner peripheral side (the inner peripheral side of the cylindrical hole) of the second insulating members M22 and M23, and the second case M31 is directed from the outside to the inside of the second mounting device M2. The second support member M33 and the rod-like electrode M32 are arranged. That is, the second case M31 and the second support member M33 are interposed between the outer peripheral surface of the internal rod-like electrode M32 and the inner peripheral surfaces of the second insulating members M22 and M23.

  The second case M31 is a metal housing that houses a part of the insulating second support member M33 and the rod-like electrode M32 and that has a hollow structure inside. The second case M31 has a first opening M34 penetrating the side surface on the side surface on the -X side (the side surface opposite to the side surface facing the first device). One end of the second coaxial cable H is inserted from the first opening M34 and connected to the end of the rod-like electrode M32 on the −X side (the side opposite to the end facing the first device). The second case M31 has a second opening M35 penetrating the side surface on the side surface on the + X side (side surface facing the first device).

  The second support member M33 is made of an insulating member, and supports the rod-like electrode M32 inside the second case M31 so that the rod-like electrode M32 does not contact the second case M31. The second support member M33 also has an opening (not shown) penetrating the side surface on the second case M31 and the side surface on the −X side (the side surface opposite to the side surface facing the first device). One end of the coaxial cable H is inserted.

  As described above, the rod-shaped electrode M32 is a member having a cylindrical shape made of metal for forming the capacitor M together with the cylindrical electrode M72, and the pipe P is formed from the second device M200 toward the first device M800. It has a structure protruding from the second opening M35 along the X direction.

  The first coaxial cable L is connected to the terminals Lc and Lp of the impedance measuring unit 400 via, for example, a T-type BNC connector (not shown), and the second coaxial cable H is connected to, for example, a T-type BNC connector. To the terminals Hc and Hp of the impedance measuring unit 400 (not shown). And the measuring apparatus 1 can perform the impedance measurement of a capacitor | condenser via these. The first coaxial cable L and the second coaxial cable H are respectively connected to the first case M71 and the second case M31 at the outer skin portion of the coaxial cable. The first case M71 and the second case M31 are electrically connected by a conductive cable (not shown), and when the measuring apparatus 1 measures the capacitance of the capacitor, the second case M31, the conductive cable, The guard current from the automatic balancing bridge is passed through one case M71 to reduce noise during measurement.

  As described above, the capacitor M of the present embodiment is formed by using the atmosphere as a dielectric in the region where the rod-like electrode M32 and the cylindrical electrode M72 face each other.

  The value of the capacitance of the capacitor M is determined according to the distance D1 between the first device M800 and the second device M200 in the X direction. Accordingly, it is possible to obtain the variation of the distance D1 based on the variation of the measured value of the capacitance of the capacitor M.

  That is, in this embodiment, based on the measured value of the capacitance of the capacitor M, the change in the area S facing the outer peripheral surface of the rod-like electrode M32 and the inner peripheral surface of the cylindrical electrode M72 as shown in Expression 7. Can be calculated.

（Ｃは静電容量（Ｆ）、ε_rは電極間に挟まれる誘電体の比誘電率、ε₀は真空の誘電率（Ｆ／ｍ）、ｄは電極間距離（ｍ）、Ｓは電極が対向する部分の表面積（ｍ²）を表す。また、Ｃ及びＳの末尾の１、２は、今回の測定値と前回と測定値を表す）
そして、本実施形態では、筒状電極Ｍ７２、棒状電極Ｍ３２で形成されるＸ方向の切断面は、Ｘ方向の位置によらず同一となっており、筒状電極Ｍ７２の外周面と、棒状電極Ｍ３２の内周面とで対向する面積Ｓの変化量から、配管Ｐの表面のＸ方向の歪を算出している。

(C is the capacitance (F), ε _r is the relative permittivity of the dielectric sandwiched between the electrodes, ε ₀ is the vacuum permittivity (F / m), d is the distance between electrodes (m), and S is the electrode Represents the surface area (m ² ) of the facing part, and the last 1 and 2 of C and S represent the current measured value, the previous measured value, and the measured value)
In this embodiment, the cut surface in the X direction formed by the cylindrical electrode M72 and the rod electrode M32 is the same regardless of the position in the X direction, and the outer peripheral surface of the cylindrical electrode M72 and the rod electrode The strain in the X direction on the surface of the pipe P is calculated from the amount of change in the area S facing the inner peripheral surface of M32.

  In the present embodiment, as described above, the change in the physical quantity due to the distortion of the pipe P is detected as the change in the capacitance of the capacitor.

  As described above, according to the present embodiment, the measurement frequency of the AC voltage applied to the capacitor can be easily and accurately set in the impedance measurement performed when detecting the change in the capacitance of the capacitor. As a result, the user of the measuring apparatus does not need to perform the work of measuring the impedance of the capacitor at an appropriate measurement frequency and determining whether the measurement frequency is an appropriate value as a sample check.

Second Embodiment
The present embodiment is different from the first embodiment in that the measured value of the insulation resistance Rp ′ between the electrodes is used when setting the insulation resistance Rp ′ between the electrodes in S1.

  The surface state of the capacitor electrodes changes with temperature and aging, and the insulation resistance between the capacitor electrodes changes accordingly. This embodiment is particularly useful when such a capacitor whose insulation resistance between the electrodes is likely to change is to be measured. Specifically, in the first embodiment, the capacitor M is configured by using the cylindrical electrode M72 and the rod-shaped electrode M32 as electrodes and the atmosphere between the cylindrical electrode M72 and the rod-shaped electrode M32 as a dielectric. Then, while the dielectric constant of the atmosphere does not change significantly, the insulation resistance Rp ′ between the electrodes varies greatly depending on the contamination state of the electrode surface and the ambient temperature. In such a case, in order to calculate an accurate simulation result in step S1, it is necessary to accurately grasp the insulation resistance Rp ′ (equivalent parallel resistance) of the insulating material between the electrodes.

  Hereinafter, aspects of the present embodiment will be described. In addition, description is abbreviate | omitted about the structure which is common in 1st Embodiment.

  FIG. 8 shows a measurement flow in the present embodiment.

  This embodiment is the same as the first embodiment except that the step S0 is performed as a preparation step before the step S1.

  S0 is a step of measuring the insulation resistance between the electrodes of the capacitor M.

  Note that the measuring apparatus 1 ′ of this embodiment has an insulation resistance measuring unit 700 as an internal configuration as shown in FIG. 9. The insulation resistance measuring unit 700 includes a power source and an ammeter that output a constant DC voltage, and can apply a DC voltage to the capacitor M to measure the insulation resistance Rp ′ between the electrodes of the capacitor M. Yes. The insulation resistance measurement unit 700 may be configured integrally with the impedance measurement unit 400 by adding a configuration that can apply a DC voltage to the capacitor in the impedance measurement unit 400.

  Therefore, in this process, a constant DC voltage is applied between the electrodes of the capacitor M using the above-described insulation resistance measuring unit 700, and the insulation resistance between the electrodes is determined by the current value of the leakage current flowing through the capacitor M at that time. taking measurement. FIG. 10 shows current characteristics when a DC voltage is applied to the capacitor. When a DC voltage is applied to the capacitor, charging current and leakage current flow in time series. The charging current is a current that flows through the capacitor during charging, and the leakage current is a constant current that flows after a certain time after the influence of the charging current is reduced, and a current value corresponding to the insulation resistance between the electrodes flows. In this embodiment, the insulation resistance between the electrodes is measured based on the current value of the leakage current (the value obtained by dividing the applied DC voltage by the current value of the leakage current is defined as the insulation resistance between the electrodes).

  In the step S1 of the present embodiment, data indicating the relationship between the measurement frequency f and the loss coefficient D value is calculated by simulation using the insulation resistance Rp ′ between the electrodes measured in the step S0, and the step S2 is performed. Then, the measurement frequency fd is determined based on the data.

  As described above, according to the present embodiment, by using the actually measured insulation resistance Rp ′ between the electrodes, the measurement frequency when performing impedance measurement can be set to a more appropriate value.

  In particular, when measuring the distortion of piping due to use in a high temperature environment for many years as described above, the insulation resistance between the electrodes of the capacitor may change, and the setting of the measurement frequency is complicated. However, according to the present embodiment, an appropriate measurement frequency can be set even when the insulation resistance between the electrodes of the capacitor changes.

  In the present embodiment, in the step S0, the insulation resistance Rp ′ between the electrodes of the capacitor may be measured under substantially the same temperature condition as the impedance measurement. Specifically, the insulation resistance Rp ′ (equivalent parallel resistance) between the electrodes may change depending on the temperature. And if the temperature conditions which measure impedance are the piping demonstrated in 1st Embodiment, since it is under a high temperature environment (about 500 degreeC), the insulation resistance Rp 'between electrodes will fluctuate compared with a normal temperature environment. Tend to.

Thus, when the simulation of the step S1 is performed, the measurement frequency when performing impedance measurement by using the insulation resistance Rp ′ between the electrodes measured under substantially the same temperature condition as the impedance measurement. Can be set to a more appropriate value. <Third Embodiment>
This embodiment is different from the first embodiment in that the reference value C _{0 of the} capacitance of the capacitor is changed in accordance with the distortion of the pipe P in the step S1.

  Hereinafter, aspects of the present embodiment will be described. In addition, about the structure which is common in 1st Embodiment, it abbreviate | omits.

  The capacitance of the capacitor varies according to the distance between the electrodes and the surface area of the portion where the electrodes face each other, as shown in the first embodiment (FIG. 7, Formula 6 etc.). Therefore, when the strain of the piping P is accumulated, the capacitance of the capacitor at the time of measurement greatly changes from the initial design value. In such a case, an accurate simulation result cannot be calculated even if a simulation in the step S1 is performed based on a design value when the amount of displacement in the X direction of the capacitor is assumed to be zero.

Therefore, in the present embodiment, the reference value C _{0 of the} capacitance of the capacitor is changed according to the strain of the pipe P, and the simulation in the step S1 is performed. Specifically, in this embodiment, the measured value of the capacitance of the capacitor calculated by the previous impedance measurement is set as the reference value C ₀ of the capacitance of the capacitor, and the measurement frequency f and the loss factor are calculated by simulation. Data indicating the relationship between the D values is calculated.

At this time, for example, data related to the measurement value of the capacitance when impedance measurement was performed in the past for the capacitor to be measured is stored in the storage unit 200 in association with the measurement time (for example, date and time). In addition, when the user inputs the capacitor to be measured to the input unit 500, the time interval from the current impedance measurement is calculated from the data regarding the past capacitance measurement value of the corresponding capacitor. The shortest measurement value, that is, the previous measurement value may be selected to set the capacitance reference value C ₀ . The “current impedance measurement time” represents the current date and time.

Then, in the S2 of the process, based on the data indicating the relationship between the measurement frequency f and the loss factor D value calculated using the reference value C ₀ of the electrostatic capacity of the capacitor determines the measurement frequency f _d.

  This makes it possible to set the measurement frequency when performing impedance measurement to a more appropriate value.

When the distortion of the surface of the pipe P can be predicted, the design value of the capacitor M (electrical resistivity of the dielectric, the distance between the electrodes, the surface area of the part facing the electrode, the relative dielectric constant of the dielectric) and the pipe Even if the electrostatic capacity of the capacitor M is calculated (predicted) based on the predicted value of the distortion of the surface of P using Equation 6, the predicted value may be set as the reference value C ₀ of the electrostatic capacity of the capacitor. Good.

<Other embodiments>
In each of the above embodiments, the cylindrical electrode M72 included in the first device M800 and the rod-shaped electrode M32 included in the second device M200 are used as electrodes, and the capacitor between the cylindrical electrode M72 and the rod-shaped electrode M32 is used as a dielectric. Although M is formed, the dielectric material is not limited to the air but can be applied to any insulating material.

  In each of the above embodiments, the capacitor M is formed by the first device M800 and the second device M200. However, if the structure can detect a change in physical quantity due to strain as a change in the capacitance of the capacitor, the capacitor The structure of is arbitrary.

  Further, the method for setting the reference value of the capacitance and the method for setting the insulation resistance between the electrodes described in the above embodiments can be arbitrarily combined.

  Moreover, the impedance measuring method of this invention can be applied to arbitrary objects other than piping. In each of the above embodiments, the impedance measurement unit 400 performs impedance measurement by the automatic balance bridge method. However, the present invention can be used for any impedance measurement method, and can be applied to, for example, the IV method, the AC bridge method, and the resonance method.

  Further, in each of the above embodiments, the case where the capacitance type sensor composed of the capacitor is used for measuring the strain of the object has been described. However, in addition to the measurement of the strain, the measurement of the change in pressure and the measurement of the change in acceleration are performed. It can also be used for a capacitive sensor that performs the above.

=== Conclusion ===
From the above, the above embodiments can be described as follows.

Each of the above embodiments is an impedance measurement method for detecting a change in capacitance of a capacitor, and is a parallel equivalent circuit model based on a reference value C ₀ of the capacitance of the capacitor and an insulation resistance Rp ′ between the electrodes of the capacitor. A first step of calculating data indicating the relationship between the measurement frequency f and the loss coefficient D value in impedance measurement (in the above embodiment, corresponding to the data shown in FIG. 6), and the measurement frequency f and loss Based on the data indicating the relationship between the coefficient D values, the first frequency (corresponding to the measurement frequency at which the loss factor is 0.1 in the above embodiment) and the second frequency higher than the first frequency (the above embodiment). Then, the second step of determining the measurement frequency f _d within the range between the measurement frequency f _d and the measurement frequency f _d determined in the second step. Disclosed is an impedance measurement method comprising: a third step of measuring the impedance of the capacitor using the AC voltage of the first step; and a fourth step of calculating a measured value of the capacitance of the capacitor based on the measurement result of the impedance measurement. To do.

  This makes it possible to easily and accurately set the measurement frequency of the AC voltage applied to the capacitor when measuring the capacitance of the capacitor.

  Here, the first frequency may be a measurement frequency when the loss coefficient is approximately 0.1. In addition, the second frequency may be a measurement frequency when the loss factor is approximately 0.001.

Here, the first step is based on the reference value C ₀ of the capacitance of the capacitor and the insulation resistance Rp ′ between the electrodes of the capacitor. Data indicating the relationship may be calculated.

  Here, the insulation resistance Rp ′ between the electrodes of the capacitor may be set based on a leakage current value that flows when a DC voltage is applied to the capacitor.

  Here, the insulation resistance Rp ′ between the electrodes of the capacitor may be set based on at least a leakage current value measured under substantially the same temperature condition as the temperature measurement condition in the third step. Thereby, when measuring the impedance of the capacitance of the capacitor, the measurement frequency of the AC voltage applied to the capacitor can be set more accurately.

  Here, the first frequency is a measurement frequency when the loss factor is approximately 0.05, and the second frequency is a measurement frequency when the loss factor is approximately 0.001. Good.

  Here, the capacitor may be a capacitor having a capacitance reference value of 1 nF or less.

Here, the capacitor has a first electrode body M7 fixed on the surface of the object P, and a surface of the object so that the capacitor can move independently of the first electrode body M7 to a position facing the first electrode body M7. The first electrode body M7 and the second electrode body M3 are formed on the basis of the measured capacitance value C of the capacitor in order to determine the distortion of the surface of the object P. You may have further the 5th process of calculating the change of distance. At this time, the reference value C ₀ of the capacitance of the capacitor is a measured value C of the capacitance of the capacitor calculated by past impedance measurement, and is selected based on the time interval from the current impedance measurement. One measured value C may be used. This makes it possible to reflect changes in the capacitance of the capacitor caused by distortion on the surface of the object when measuring the capacitance of the capacitor, and to set the measurement frequency of the AC voltage applied to the capacitor more accurately. can do.

Further, the reference value C ₀ of the capacitance of the capacitor may be set based on the design value of the capacitor and the predicted value of the distortion of the object. This makes it possible to reflect changes in the capacitance of the capacitor caused by distortion on the surface of the object when measuring the capacitance of the capacitor, and to set the measurement frequency of the AC voltage applied to the capacitor more accurately. can do.

Each of the above embodiments is an impedance measuring device 1, 1 ′ that detects a change in the capacitance of the capacitor, and includes a reference value C ₀ of the capacitance of the capacitor and an insulation resistance Rp ′ between the electrodes of the capacitor. A first calculation unit 100 for calculating data indicating the relationship between the measurement frequency f and the loss factor D value in the impedance measurement by simulation using the parallel equivalent circuit model, and data indicating the relationship between the measurement frequency f and the loss factor D value An impedance measurement unit 400 that performs impedance measurement using an AC voltage having a measurement frequency f _d determined within a range between the first frequency and a second frequency higher than the first frequency, and impedance measurement A second calculation unit 100 that calculates a capacitance measurement value of the capacitor based on the impedance measurement result of the unit 400. It is intended to disclose a dance measuring device 1, 1 '.

  This makes it possible to easily and accurately set the measurement frequency of the AC voltage applied to the capacitor when measuring the capacitance of the capacitor.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Measuring apparatus 100 Control part 200 Memory | storage part 300 Display part 400 Impedance measurement part 410 Oscillator 420 Current voltage conversion part 421 Reference resistor 422 Zero level detector 430 Vector ratio detection part 431 Vector voltmeter 500 Input part 600 Bus 700 Insulation resistance measurement Part M Capacitor C Capacitance Rp Equivalent parallel resistance f Measurement frequency P Piping

Claims (12)

An impedance measurement method for detecting a change in capacitance of a capacitor,
A first step of calculating data indicating a relationship between a measurement frequency and a loss factor in impedance measurement by a simulation using a parallel equivalent circuit model based on a reference value of the capacitance of the capacitor and an insulation resistance between the electrodes of the capacitor When,
A second step of determining a measurement frequency within a range between a first frequency and a second frequency higher than the first frequency based on data indicating a relationship between the measurement frequency and a loss factor;
A third step of measuring the impedance of the capacitor using an alternating voltage of the measurement frequency determined in the second step;
A fourth step of calculating a measured value of the capacitance of the capacitor based on the measurement result of the impedance measurement;
An impedance measurement method comprising: The impedance measurement method according to claim 1, wherein the first frequency is a measurement frequency when the loss factor is approximately 0.1. The impedance measurement method according to claim 1, wherein the second frequency is a measurement frequency when the loss factor is approximately 0.001. In the first step, data indicating the relationship between the measurement frequency and the loss factor is calculated by simulation using Formula A based on the reference value of the capacitance of the capacitor and the insulation resistance between the electrodes of the capacitor. The impedance measurement method according to any one of claims 1 to 3, wherein:

(Where Rp ′ is the insulation resistance (Ω) between the electrodes, f is the measurement frequency (Hz), and C ₀ is the reference value (F) of capacitance) 5. The impedance measuring method according to claim 1, wherein an insulation resistance between the electrodes of the capacitor is set based on a leakage current value that flows when a DC voltage is applied to the capacitor. . The insulation resistance between the electrodes of the capacitor is set based on at least the leakage current value measured under substantially the same temperature condition as the temperature measurement condition in the third step. The impedance measurement method described. The first frequency is a measurement frequency when the loss factor is approximately 0.05, and the second frequency is a measurement frequency when the loss factor is approximately 0.001. The impedance measurement method according to any one of claims 1 to 6, wherein: The impedance measuring method according to any one of claims 1 to 7, wherein the capacitor is a capacitor having a capacitance reference value of 1 nF or less. The capacitor is fixed on the surface of the object so that the capacitor can move independently of the first electrode body at a position facing the first electrode body and a first electrode body fixed on the surface of the object. Formed by the second electrode body,
The method further includes a fifth step of calculating a change in the distance between the first electrode body and the second electrode body based on a measured value of the capacitance of the capacitor in order to obtain a distortion of the surface of the object. The impedance measuring method according to claim 1, wherein the impedance measuring method is one of the following. The reference value of the capacitance of the capacitor is a measured value of the capacitance of the capacitor calculated by a past impedance measurement, and is selected based on a time interval from the current impedance measurement. It is a measured value. The impedance measuring method of Claim 9 characterized by the above-mentioned. The impedance measurement method according to claim 9, wherein the reference value of the capacitance of the capacitor is set based on a design value of the capacitor and a predicted value of distortion of the surface of the object. An impedance measuring device for detecting a change in capacitance of a capacitor,
First, data representing a relationship between a measurement frequency and a loss factor in impedance measurement is calculated by a simulation using a parallel equivalent circuit model based on a reference value of the capacitance of the capacitor and an insulation resistance between the electrodes of the capacitor. A calculation unit;
Based on the data indicating the relationship between the measurement frequency and the loss factor, impedance measurement is performed using an alternating voltage of the measurement frequency determined within a range between the first frequency and the second frequency higher than the first frequency. An impedance measurement unit for performing
A second calculation unit that calculates a measured value of the capacitance of the capacitor based on a measurement result of impedance measurement by the impedance measurement unit;
An impedance measuring device comprising:

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