Important Knowledge for Strain Measurement

Select a strain gauge that suits the material of the measurement target

选择适合测量目标材料的应变量表，以取消靶标的温度变化（热膨胀）的影响。

For general steel materials, the length changes by 11 μm (that is, 11 μST) per meter with a temperature change of 1°C (1.8°F).

This apparent strain ε_tempis expressed as follows, where the linear expansion coefficient of the target measurement is β, the linear expansion coefficient of the strain gauge is β_G, the temperature coefficient of the strain gauge resistor is α_G, and the gauge factor is K.

ε_temp= (β − β_G） +α_G/K

Examples of linear expansion coefficients

钢材材料：11.7 × 10^-6/°C (°F)

SUS304：16.2×10^-6/°C (°F)

一个luminum alloy:23.4 × 10^-6/°C (°F)

因此，选择一个尺寸，其线性膨胀系数已校正了测量目标的材料，以使表观应变εε_temp“0.” For general strain gauges, the type is suffixed with the integer part of the linear expansion coefficient, such as “11” and “16.”

Select a strain gauge whose length and width match your measurement purpose

Select a strain gauge whose length and width are suited to the material of the measurement target and your measurement purpose. For example, use a narrow strain gauge for narrow measurement targets such as pipes and round bars.

仪表长度用于不同测量目的的示例

对于受到高速现象（例如休克，圆形表面和应力浓度下的表面）的表面：0.2 to 1 mm

For measurement of metals and plastics:大约2至10毫米

用于测量木材和复合材料：大约10至20毫米

For measurement of concrete:30毫米或更长时间（砾石粒度3倍或更长）

选择满足适用条件的应变量表，例如安装环境和接线长度

一般的箔量规是由“高级合金”制成的，该合金含有54％Cu和46％Ni，并且厚度为几微米。对于基础部分，使用聚酯和聚酰亚胺。因此，在需要水密性和高温耐药性时使用专用的应变仪。

If you want to enhance the measurement accuracy
Click here for key points for improvement.

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Check the attachment status of the strain gauge

Have you properly completed the“preprocessing” for attachment在“应变测量基础”中描述？您是否在应变量表的背面放了足够的粘合剂？检查以下几点以确保应变量表已正确连接。

Whether the adhesive has overflown properly
检查粘合剂是否均匀地溢出。量规不太可能在粘合剂没有溢出的地方牢固地固定。

Whether the attached surface is free of dust and bubbles
如果在附着之前将灰尘或气泡保留在表面上，则造成测量误差。

Whether the lead wires are broken
应变表的铅线非常细，如果在附着过程中施加力，可能会损坏。用测试仪测量仪表的两条电线之间的电阻。如果指示了120Ω，它们不会被打破。

纠正应变计的量规因子

一个lthough strain gauges have been manufactured with a reference gauge factor of 2.00, the actual factor is approximately 1.9 to 2.2. Because the gauge factor of a strain recorder is fixed at 2.00, a 0.1 difference in the gauge factor will lead to an error of approximately 5%. As such, correction with the scaling function of the recorder must be performed by using the gauge factor K described on the box of the strain gauge.

ε₀：

真正的压力

ε：

测得的应变

ε₀=ε×2.00/k

■ Correction example
当使用具有2.09的量规系数的应变量表时

ε₀=ε×2.00/k= ε × 2.00/2.09 = 0.957 × ε

Correct the angle error

应变量表方向之间的5°差异导致误差约1％。如果附件的方向不匹配抄写线，请使用泊松比（V）执行缩放和校正。

ε₀：

真正的压力

ε：

测得的应变

ν：

泊松的比例

θ：

角（°）

ε = ε₀{（1-ν） +（1 +ν）cos2θ}/2

因为泊松比通常约为0.3，所以

ε = ε₀(0.7 + 1.3 cos2θ)/2
ε₀=2ε/（0.7 + 1.3cos2θ）

参考：基于角度的灵敏度错误，泊松比为0.3
1° = 0.03%, 2° = 0.16%, 3° = 0.36%, 4° = 0.64%, 5° = 1.00%

纠正接线长度的效果

如果导线线扩展，则产生其接线电阻的效果。对于细线，延长乘20 m产生的误差约为7％。对于长长的接线长度，请使用以下公式执行缩放和校正。

ε₀：

真正的压力

ε：

测得的应变

γ：

Lead wire resistance (round-trip)

ε₀= ε (1 + γ/R)

■参考：
Relationships between the nominal cross-sectional area of a lead wire and the resistance (round-trip) per meter

0.08毫米²- >0.44Ω
0.18毫米²->0.2 Ω
0.3 mm²- >0.117Ω
0.5毫米²->0.07 Ω
0.75毫米²->0.047 Ω

Correct the temperature effect

To achieve accurate measurement in an environment with temperature change, it is necessary to use a self temperature compensating-type strain gauge or to compensate the temperature using the two-gauge method. For a long wiring length, the three-wire system offers better measurement accuracy.

If you want to enhance the measurement accuracy
Click here for key points for improvement.

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