Short Answer:
In strain gauges, temperature compensation is used to eliminate the errors caused by changes in temperature, which can affect the accuracy of strain measurements. When temperature changes, it not only causes actual strain in the material but also affects the resistance of the strain gauge itself.
Temperature compensation works by using a second, identical strain gauge that is not subjected to mechanical strain but is exposed to the same temperature. This compensating gauge is connected in a Wheatstone bridge circuit to cancel out the temperature effects, ensuring that only the actual mechanical strain is measured.
Detailed Explanation:
Temperature Compensation in Strain Gauges
Strain gauges are devices that measure the strain or deformation in a material when subjected to stress. They work by detecting changes in electrical resistance as the material stretches or compresses. However, temperature changes can also affect the resistance of the gauge, leading to inaccurate readings. To ensure reliable results, temperature compensation is necessary.
When temperature rises or falls, it causes:
- Thermal expansion or contraction of the object, which may be interpreted as mechanical strain.
- Change in resistance of the strain gauge material due to its temperature coefficient of resistance (TCR).
Without compensation, the strain gauge might show a strain reading even when no mechanical stress is applied, just because of the change in temperature. Temperature compensation helps eliminate this false strain.
How Temperature Compensation Works
- Use of a Dummy Gauge
The most common method of temperature compensation involves using two strain gauges:- One is the active gauge, which is bonded to the part of the object where strain is to be measured.
- The other is the dummy gauge, which is identical in material and characteristics but is mounted in such a way that it experiences the same temperature but no mechanical strain.
- Connection in Wheatstone Bridge
Both gauges are connected in a Wheatstone bridge circuit. This setup allows any changes in resistance due to temperature to be cancelled out because both gauges react the same way to temperature but differently to strain:- The active gauge changes resistance due to both strain and temperature.
- The dummy gauge changes resistance due to temperature only.
- Balancing Out the Temperature Effect
In the bridge, the temperature-induced resistance changes from both gauges oppose each other, thus eliminating the error. The output voltage from the bridge will now only reflect the mechanical strain. - Self-Temperature Compensation Strain Gauges
Some strain gauges are manufactured with materials that have a known thermal coefficient, matched to the material of the object being tested. These gauges automatically adjust for temperature effects, reducing the need for external compensation. - Use of Signal Conditioners and Electronic Circuits
In modern digital systems, temperature sensors and microcontrollers can be used to digitally compensate for temperature effects by adjusting the readings based on temperature input.
Importance of Temperature Compensation
- Ensures accuracy in varying temperature conditions
- Prevents false readings due to thermal expansion
- Useful in outdoor or industrial applications with fluctuating temperatures
- Makes the gauge suitable for long-term monitoring and precision measurements
Applications Where It Is Used
- Aerospace structural testing
- Bridge and building stress monitoring
- Automotive and engine part testing
- Industrial machines under varying operating conditions
Conclusion
Temperature compensation in strain gauges is crucial to ensure that the strain measured is only due to mechanical forces and not due to temperature changes. By using dummy gauges, Wheatstone bridge circuits, and temperature-matched materials, errors caused by temperature are effectively removed. This allows strain gauges to provide accurate and consistent readings in real-world conditions where temperature variation is unavoidable.