Thermal Output

Once an installed strain gage is connected to a strain indicator and the instrument balanced, a subsequent change in the temperature of the gage installation will normally produce a resistance change in the gage. This temperature-induced resistance change is independent of, and unrelated to, the mechanical (stress-induced) strain in the test object to which the strain gage is bonded. It is purely due to temperature change, and is thus called the thermal output of the gage.

Thermal output is potentially the most serious error source in the practice of static strain measurement with strain gages. In fact, when measuring strains at temperatures remote from room temperature (or from the initial balance temperature of the gage circuit), the error due to thermal output, if not controlled, can be much greater than the magnitude of the strain to be measured. At any temperature, or in any temperature range, this error source requires careful consideration; and it is usually necessary to either provide compensation for thermal output or correct the strain measurements for its presence.

Page 2 of 17