Change in temperature causes strain gages to give an output, even under no-load conditions. To counter this, Strain gages are designed to compensate the change . This is called Self-temperature Compensation or STC.
Gages are built with different amounts of Compensation , specific to the Thermal coefficient of expansion of the materials on which they are bonded. the correct STC gages will be insensitive to a small range of temperature change around room temperature.
They will however produce large signals for big changes in temperature, and need to be corrected to cancel out the error in the
measurement of strain.
In this video, a few methods for compensating the thermal output of gages are described, using dummy gages for the purpose.
There are instances where dummy gages cannot be used for practical reasons. For such cases, The StrainSmart software along the Data Loggers from Micro Measurements has the ability to correct for thermal output for significant improvement in the accuracy of strain measurements. This is done by entering the Coefficients for thermal output, given on each packet of the gages, in the appropriate section of the sensors page in the software.
Additionally, it is possible to generate the compensation parameters by measuring the thermal output for a range of temperatures, and entering these values in the StrainSmart software. The software generates the polynomial expression for correction, and applies this to the readings of strain during the test.
For this purpose, the data loggers can be set up with a a temperature measurement channel , which will be monitored for calculating the correction to be applied .
Strain gages with the correct STC should be chosen at all times. If a gage with the wrong STC is used, the errors can be huge.. In this video, gages with the wrong STC are used for demonstration only, as the thermal output shows up readily, and also to highlight the large extent of error that will occur for even small variations in temperature if STC is not matched to the test part.
To avoid errors in Strain measurement, it is important to use temperature compensation methods described here, starting with choosing strain gages with the correct STC.