JP2007315853A - Strain gauge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strain gauge for preventing baking out, and measuring a strain in a wide measurement range. <P>SOLUTION: The strain gauge is configured so as to change the electrostatic capacitance of a capacitor, formed by electrodes 12a, 12b when the second electrode 12b is reciprocated from/to an interior of the first electrode 12a, according to the strain in a measured object 3. A first insulating support 14a is extended toward the second electrode 12b from the first electrode 12a, an extended part is provided with a through-hole that communicates with the internal space of the first electrode 12a, and the second electrode 12b is guided and inserted into the through-hole. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mechanical structure of a strain measuring device.

  For example, a strain measurement method is known as one of methods for inspecting the remaining life of heat-sensitive metal welds such as boilers, turbines, and their piping in thermal power plants. This strain measurement method is for inspecting the remaining life of a metal welded part etc. from the strain on the surface of the object to be measured. However, since these surfaces to be measured have a surface temperature of 600 ° C. or higher, the measurement is performed at a high temperature. It is necessary to have a strain gauge capable of

  Conventionally, such strain measurement at a high temperature has been performed using a strain gauge 1 as shown in FIGS. 1 and 2, for example (see Non-Patent Document 1). The outline of the strain gauge 1 will be described below.

FIG. 1 is a schematic plan view of the strain gauge 1, and FIG. 2 is a schematic sectional view of the strain gauge 1. As shown in these drawings, the strain gauge 1 has a structure in which two rectangular metal plates (5a, 5b) curved in an arch shape are overlapped with a gap therebetween. Between these two metal plates (5a, 5b), a pair of electrode plates (7a, 7b) forming a capacitor are disposed opposite to each other. According to such a configuration, the distance between the electrode plates (7a, 7b) changes as the surface of the measuring object 3 expands and contracts, so that the capacitance of the capacitor formed by the electrode plates (7a, 7b). Changes. Therefore, the strain on the surface of the measurement object can be measured by detecting the capacitance of the capacitor.
REMNANT LIFE MONITORING, APPLICATIONS REPORT, AUTOMATIC SYSTEMS LABORATORIES LTD; JULY 1972, Vol, 119, No7

  However, the configuration that detects the change in the distance between the opposing electrode plates (7a, 7b) as described above has a small measurable range width, and thus cannot measure strain over a wide strain range. On the other hand, in order to measure a wide range of strain, one electrode is guided so as to be displaceable with respect to the other electrode, and the electrode is relatively displaced according to the strain on the surface to be measured so that the opposing area of both electrodes It can be considered that the capacitance between the electrodes changes due to the change. With this configuration, when the measuring device is placed at a high temperature, there is a possibility that seizure may occur at the sliding portion that guides the electrode in a displaceable manner.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a strain measuring apparatus capable of measuring strain in a wide measuring range while preventing burning.

  In order to solve the above-mentioned problem, the invention described in claim 1 is a first electrode configured in a cylindrical shape, and is capable of moving back and forth inside the first electrode, and constitutes a capacitor together with the first electrode. A second electrode that supports the first electrode; a second insulating support that supports the second electrode; and the first and second insulations. An attachment member for attaching each of the supports to the measurement object, and the capacitance of the capacitor by moving the second electrode forward and backward inward of the first electrode according to the strain of the measurement object. The first insulating support extends to the second electrode side of the first electrode and communicates with the inner space of the first electrode at the extended portion. A through hole is provided, and the second electrode is inserted into the through hole and guided. The features.

  According to the present invention, since the first insulating support made of ceramic is configured to guide the second electrode, the insulating support and the second electrode are seized when used at a high temperature. Can be prevented. Furthermore, since the second electrode advances and retracts while being guided by the first insulating support relative to the first electrode according to the amount of strain on the surface of the measurement object, the first electrode and the second electrode overlap. Since it is possible to measure up to a certain length, the measurement range can be widened.

  According to the second aspect of the present invention, a coil, a metal body capable of moving back and forth inside the coil, an insulating support that supports the coil and the metal body, respectively, and the insulating support as a measurement object, respectively. A strain measuring device configured to change electrical characteristics of the coil by moving the metal body forward and backward relative to the coil, the first member supporting the coil. The insulating support extends to the metal body side of the coil, and a through-hole communicating with the inner space of the coil is provided in the extended portion, and the metal body is inserted and guided through the through-hole. It is characterized by.

  ADVANTAGE OF THE INVENTION According to this invention, the distortion measuring apparatus which can measure distortion in a wide measurement range can be provided, preventing baking.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The strain measuring device according to the present invention measures strain of a metal material welded portion that is exposed to high temperatures and is easily affected by heat, such as a welded portion of a boiler of a thermal power plant and various steam pipes. Used for. First, the outline of the strain measuring apparatus and the measurement principle will be described.

  FIG. 3 is a schematic diagram of the strain measuring apparatus 10. As shown in the figure, the strain measuring device 10 includes a cylindrical first electrode 12a and a second electrode 12b inserted into the hollow portion of the first electrode 12a. A predetermined interval is provided between the inner peripheral surface of the first electrode 12a and the outer peripheral surface of the second electrode 12b, and both electrodes (12a, 12b) form a capacitor. A capacitance measuring circuit 15 is connected to the electrodes (12a, 12b), and the capacitance of the capacitor is measured by the capacitance measuring circuit 15. Then, strain is obtained from the measured capacitance by the strain detection circuit 17 and displayed on the display device 18. The electrodes (12a, 12b) are respectively supported by the insulating supports (14a, 14b), and are fixed to the surface of the measurement object 3 by the attachment member 16.

  The ceramic insulating support 14a that supports the first electrode 12a extends from the first electrode 12a toward the second electrode 12b. A through hole 13 communicating with the inner space of the first electrode 12a is provided in the extended portion, and the second electrode 12b is inserted into the through hole 13 and guided.

  According to the above configuration, when the surface of the measurement object 3 is distorted, the overlap length of the first electrode 12a and the second electrode 12b is changed by the advance / retreat movement of the electrodes (12a, 12b). For this reason, since the opposing area of the electrodes (12a, 12b) changes, the electrostatic capacitance formed by these electrodes (12a, 12b) also changes. Therefore, the strain can be obtained by the strain detection circuit 17 from the capacitance measured by the capacitance measurement circuit 15.

  In addition, since the ceramic first insulating support 14a that supports the first electrode 12a is configured to serve as a bearing for the second electrode 12b, the second electrode 12b is seized even when used at a high temperature. There is nothing. Furthermore, since the second electrode 12b advances and retreats while being guided by the first insulating support 14a with respect to the first electrode 12a according to the amount of strain on the surface of the measurement object, the measurement range can be widened.

  The strain data detected by the strain measuring device 10 can be used in various ways. For example, it may be displayed on the screen by the display device 18 so that the person in charge can visually read the distortion, or the distortion data is automatically transmitted to the server via a wireless or wired communication line. It may be possible to input to a computer and analyze it.

  FIG. 4 shows the temperature change of the output voltage of the strain detection circuit 17 when the positional relationship between the first electrode 12a and the second electrode 12b is constant. Since the strain measuring apparatus 10 has the temperature characteristics as shown in the figure, a compensation circuit (not shown) may be provided to compensate for the temperature characteristics.

  Next, the material which comprises the distortion measuring apparatus 10 is demonstrated. First, as a material constituting the electrodes (12a, 12b), a metal material that does not oxidize even when used at a high temperature is used. In this specification, not oxidizing means that the oxidation does not proceed to the inside of the metal even at a high temperature of, for example, 500 ° C. or higher.

  If the electrodes (12a, 12b) are made of a metal material that does not oxidize at high temperatures, the change in properties of the electrodes (12a, 12b) is reduced even when used for a long time at high temperatures. Therefore, the measurement error can be reduced.

  Examples of the metal material that does not oxidize at a high temperature of 500 ° C. or higher include a nickel base alloy, a chromium base alloy, a cobalt base alloy, and SUH21, SUH409, SUH409L, SUH446, SUS405, SUS410L, SUS430, containing 9% or more of Cr. SUS430JIL, SUS436JIL, SUH1, SUH3, SUH4, SUH11, SUH600, SUH616, SUS403, SUS410, SUS410JI, SUS431, SUH31, SUH35, SUH36, SUH37, SUH38, SUH309, SUH309, SUH309, SUH309, SUH309, SUH309, SUH309, SUH309, SUH309 SUS310S, SUS316, SUS316Ti, SUS317, SUS321, SUS347, S SXM14JI, SUS630, may be mentioned heat-resistant steel such as SUS 631.

  Moreover, the strain measuring apparatus 10 according to the present embodiment uses, for example, a ceramic material having a purity of 90% or more as a material constituting the insulating support 14 that supports the electrodes (12a, 12b). Examples of the ceramic material include alumina and sapphire.

  Thus, if a ceramic material with high purity is used as the insulating support 14, electrical insulation between the electrodes (12 a, 12 b) and the mounting member 16 can be ensured even at a high temperature. For example, if the purity of the ceramic material is 90% or more, sufficient electrical insulation can be realized at room temperature, but it is preferable that the purity is 99% or more so that an insulation resistance of about 5 MΩ can be realized even at a temperature near 500 ° C. More preferably, if the purity is 99.7% or more, for example, an insulation resistance of about 40 MΩ can be realized even at a temperature near 600 ° C.

  Moreover, about the shape of the 1st insulation support body 14a and its hollow part, it should just support the 2nd electrode 12b, and it is not specifically limited. For example, it may be cylindrical or prismatic. An example is shown in FIG. According to the figure, although the groove-shaped guide part 19 provided in the hollow part side of the 1st insulating support body 14a and the convex part provided in the 2nd electrode 12b side are shown, it has shown the shape. The convex portion provided on the second electrode 12b side and the groove-shaped guide portion 19 provided on the hollow portion side of the first insulating support 14a may be fitted. Thus, if the 2nd electrode 12b can be inserted along the guide part 19, it is possible to guide the 2nd electrode 12b stably.

  A plurality of guide portions 19 may be provided. As for the mode of the guide portion 19, various modifications and devices can be assumed, for example, as shown in cross-sectional views in FIGS. If the guide portion 19 is provided in this way, the first electrode 12a can easily move in the bearing even if the measuring object 3 expands and contracts, so that the first electrode 12a does not break due to stress. Furthermore, since the first electrode 12a can be stably fixed, for example, highly accurate measurement can be performed even in an environment where vibration is likely to be applied.

Table 1 is a table showing the results of comparing the high temperature characteristics of the insulating supports. According to Table 1, alumina (material symbol A-479, purity 99.5%) had good characteristics at a high temperature of about 500 ° C., and the insulation resistance at 600 ° C. was 5 MΩ. Alumina (material symbol A-480S, purity 99.7%) had good characteristics even at a high temperature of about 600 ° C., and showed an insulation resistance of 40 MΩ. Therefore, it was revealed that if high-purity alumina is used as an insulating material, strain can be measured even at high temperatures.

  FIG. 9 is a cross-sectional view of a coil-type strain measuring apparatus 100 that is another embodiment of the present invention. The coil-type strain measuring device 100 includes a coil 20, a metal body 22 that can advance and retreat inside the coil 20, a first insulating support 24 a that supports the coil 20, and a second insulating support that supports the metal body 22. The body 24b and mounting members (26a, 26b) for fixing the insulating support (24a, 24b) to the surface of the measuring object 3 are configured. And the metal body 22 is penetrated by the through-hole 13 provided in the 1st insulation support body 24a, and is guided so that a displacement in an axial direction is possible.

  Therefore, if distortion occurs on the surface of the measuring object 3, the metal body 22 moves forward and backward in the coil 20 accordingly, and the inductance generated in the coil 20 changes. That is, the coil-type strain measuring apparatus 100 can measure the strain of the measuring object 3 based on the change in the electrical characteristics of the coil 20 generated by the forward / backward movement of the metal body 22.

  According to the above configuration, a wide range of strain can be measured, and the metal body 22 is guided by the first insulating support 24a made of ceramic, so that it is seized when used at a high temperature as in the first embodiment. Can be prevented. Further, if the first insulating support 24a is provided with a guide portion, the metal body 22 can easily move inside the coil 20 and is not broken due to stress, and the metal body 22 can be stably fixed. Therefore, it becomes possible to perform highly accurate measurement.

  In the above embodiment, the case where the strain measuring device of the present invention is applied to strain measurement of a welded part of a boiler of a thermal power plant and various steam pipes is described as an example, but the present invention is not limited thereto, for example, It can also be applied to vibration measurement of automobile engines. In other words, the quietness of the engine is an important factor in automobiles, particularly high-end passenger cars. However, the engine's quietness is canceled by measuring the slight vibration generated by the engine and applying a displacement in the opposite phase to this. Can be improved. Until now, there was no device that could measure the vibration displacement of the engine that would be very hot, so an automobile having such a function has not been realized. However, with the strain measurement device of the present invention, the vibration displacement of the engine has not been realized. Measurement is possible, and the above functions can be realized. Moreover, the effect of suppressing loosening of bolts and nuts can be expected by canceling engine vibration.

It is a plane schematic diagram of a strain gauge. It is a cross-sectional schematic diagram of a strain gauge. It is the schematic of a distortion measuring device. It is a figure which shows the temperature characteristic of a distortion measuring device. It is a figure which shows the cross-sectional shape 1 of a supporting member. It is a figure which shows the cross-sectional shape 2 of a supporting member. It is a figure which shows the cross-sectional shape 3 of a supporting member. It is a figure which shows the cross-sectional shape 4 of a supporting member. It is a cross-sectional schematic diagram of a coil type distortion measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Strain meter 3 Measuring object 5a, 5b Metal plate 7a, 7b Electrode plate 10 Strain measuring device 12a, 12b Electrode 13 Through hole 14a, 14b Insulating support 15 Capacitance measuring circuit 16 Mounting member 17 Strain detecting circuit 18 Display device DESCRIPTION OF SYMBOLS 19 Guide part 20 Coil 22 Metal body 24a, 24b Insulation support body 26a, 26b Mounting member 100 Coil type distortion measuring apparatus

Claims (2)

A first electrode configured in a tubular shape;
A second electrode that is movable back and forth to the inside of the first electrode and constitutes a capacitor together with the first electrode;
A first insulating support made of ceramic that supports the first electrode;
A second insulating support for supporting the second electrode;
An attachment member for attaching the first and second insulating supports to the object to be measured,
The capacitance of the capacitor is changed by moving the second electrode forward and backward inward of the first electrode according to the strain of the measurement object,
The first insulating support extends to the second electrode side from the first electrode, and a through-hole communicating with the inner space of the first electrode is provided in the extended portion. A strain measuring apparatus, wherein the second electrode is guided through a hole. A coil, a metal body capable of advancing and retracting to the inside of the coil, an insulating support for supporting the coil and the metal body, and an attachment member for attaching the insulating support to a measurement object,
A strain measuring device configured to change the electrical characteristics of the coil by moving the metal body forward and backward relative to the coil;
The insulating support that supports the coil extends to the metal body side of the coil, and a through hole that communicates with the inner space of the coil is provided in the extended portion, and the metal body is inserted into the through hole. A strain measuring apparatus characterized by being guided.

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