JPH0226723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a strain gauge, and particularly to a capacitive strain gauge suitable for measuring large strains in high-temperature, corrosive environments.

[Prior art]

The conventional capacitive strain gauge has two
This method detects the capacitance of flat electrodes fixed to arcuate plates with different radii, and a space must be provided between the electrodes. Therefore,
Conventional capacitive strain gauges require a large space for installation and cannot be used in conductive environmental media. In addition, temperature changes in the environmental medium have a very large effect on capacitance, significantly reducing strain measurement accuracy.

[Purpose of the invention]

An object of the present invention is to provide a strain gauge that is less affected by changes in the environmental medium surrounding the strain gauge and is easy to install.

[Summary of the invention]

The main point of the present invention is to take advantage of the fact that a metal wire embedded in a thin tube through ceramics follows the expansion and contraction of the tube well, to seal a thin wire electrode into the thin tube through ceramics, and to cover it. Attach it to the object to be measured,
The purpose is to avoid the electrical influence of the environmental medium and to avoid the influence of temperature by providing a compensation electrode.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2, 3, and 4.

Electrodes 1 and 2 made of a pair of parallel heat-resistant metals
is bent into a bellows shape in order to increase the area between the wires, and is molded with ceramics 7 inside the cladding tube 5 at a position close to the mounting plate 6. Another pair of electrodes 3 and 4 having substantially the same shape are similarly molded with ceramics within the cladding tube 6 in a direction orthogonal to the vicinity of the electrodes 1 and 2. One end of the electrode wires 1 and 4 is
Connect to shield wires 9 and 11, electrode wires 2 and 3
One end of the two is connected to the same shielded wire 10. The cladding tube 5 is fixed to a mounting plate 6. The mounting plate 6 is attached to the object to be measured 8 at its periphery (for example, by spot welding or the like). Now, let us consider a case where a force is applied to the object to be measured 8 in the horizontal direction as shown in FIG. 2, and the object is placed in a high-temperature atmosphere. The mounting plate 6 and the cladding tube 5 extend horizontally through the fixing part, and the ceramic 7 inside the tube extends through the cladding tube 5 in the horizontal direction, and at the same time contracts in a direction perpendicular thereto. Accordingly, the distance between electrode wires 1 and 2 molded in ceramic becomes larger, and the distance between electrode wires 3 and 4 becomes smaller. The initial values of capacitance between electrode wires 1 and 2 and electrode wires 3 and 4 are respectively C ₁₂ and C ₃₄ , the amount of change due to external force is ΔC ^T ₁₂ and ΔC ^P ₃₄ , and the amount of change due to temperature change is ΔC ^T ₁₂ and ΔC ^T ₃₄ , ΔC ^P ₁₂ can be measured by the circuit shown in FIG. 5, and elongation due to external force in the horizontal direction can be measured. That is, if the initial C ₁₂ and C ₃₄ are set almost the same, ΔC ₁₂ = ΔC ^P ₁₂ + ΔC ^T ₁₂ ΔC ₃₄ = ΔC ^P ₃₄ + ΔC ^T ₃₄ ΔV _g = (ΔC ₁₂ − ΔC ₃₄ )×V _B / C ₁₂ Here, ΔC ^P ₃₄ = −νΔC ^P ₁₂ , (ν is Poisson's ratio) ΔC ^T ₃₄ = ΔC ^T ₁₂ ΔV _g = (1+ν) ΔC ^P ₁₂ ×V _B /C ₁₂ On the other hand, the capacitance between the electrode wires and Since there is the following relationship between C ₁₂ = A・b+l/D ₁₂ ΔC ^P ₁₂ /C ₁₂ = −ΔC ₁₂ /D ₁₂ ΔV _g V _B =−(1+ν)ΔC ₁₂ /D ₁₂ =−(1+ν)・B・ε In other words, the strain ε of the object to be measured can be measured as the unbalanced voltage of the bridge. In addition, unlike conventional resistance wire types, there is no need to ensure electrical resistance characteristics for the strands, and metals with good conductivity, such as platinum, with high ductility can be used, so the wires will break before the structure is destroyed. Never.

FIG. 6 is an example of a different shape of the electrode wire, which is a combination of comb shapes. According to this, the size of the part where the teeth of the comb are tied can be increased,
Furthermore, a durable gauge can be made.

FIG. 7 shows an example of an electrode wire manufactured by punching from a flat plate. According to this method, an electrode wire with a stable constant shape can be obtained, so that a strain gauge with constant characteristics can be manufactured.

According to this embodiment, there is no influence from external environmental media. It can measure high-temperature strain without breaking even under large deformations.

〔Effect of the invention〕

According to the present invention, strain can be measured even in a high temperature environment with a small measurement space.

[Brief explanation of drawings]

FIG. 1 is a side view of a conventional capacitive high temperature strain gauge, FIG. 2 is a plan view of the capacitive high temperature strain gauge of the present invention, FIG. 3 is a sectional view taken along the - arrow in FIG. 2, and FIG. 3 is a partially enlarged view of the electrode wire, FIG. 5 is an electric circuit diagram of one embodiment of the present invention, and FIGS. 6 and 7 are plan views of electrode shapes of other embodiments of the present invention. 1, 2... Main electrode wire pair, 3, 4... Subordinate electrode wire pair, 5... Covering tube, 6... Mounting plate, 7... Ceramics, 8... Measured object, 9, 10, 11... …
Shielded wire.

Claims (1)

[Claims] 1. A capacitive strain gauge that is attached to the surface of an object to be measured and detects the amount of expansion and contraction of the object as a change in capacitance, comprising: A capacitive strain gauge characterized by having a pair of linear electrodes. 2. A capacitive strain gauge as set forth in claim 1, characterized in that two pairs of electrodes having different amounts of change in capacitance for the same amount of expansion and contraction are provided close to each other.