Brands
Vishay Measurements Group
Interactive Guide
Tech Notes
TN-504
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Strain Gage Thermal Output
and Gage Factor Variation with Temperature |
Corrections for Thermal OutputDepending upon the test temperature and the degree of accuracy required in the strain measurement, it will sometimes be necessary to make corrections for thermal output, even though self-temperature-compensated gages are used. In any case, when making strain measurements at a temperature different from the instrument balance temperature, the indicated strain is equal to the sum of the stress-induced strain in the test object and the thermal output of the gage (plus the strain equivalent of any other resistance changes in the gage circuit). With the thermal output expressed in strain units, as in Eq. ( 504.2 ), correction for this effect is made by simply subtracting (algebraically, with sign) the thermal output from the indicated strain. 
Fig.5 - Replica of graph included on the Technical Data Sheet accompanying each package of Micro-Measurements self-temperature-compensated strain gages. As an aid to the user in correcting for temperature dependent properties, the technical data sheet in each package of Micro-Measurements A- and K- alloy strain gages includes a graph showing the thermal output and gage-factor variation with temperature. Figure 5 is typical (for A alloy) of the graphs supplied with the gages. In addition to plots of thermal output and gage factor variation, polynomial equations are provided (in both Fahrenheit and Celsius units) for the thermal output curve. Also given on the graph are two other important items of information: (1) the lot number of the strain gages, and (2) the test material used in measuring the thermal output characteristics. It should be noted that the thermal output data are specifically applicable to only gages of the designated lot number, applied to the same test material. 
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