If desired, for extensive strain measurement programs, the thermal output curve in Fig. 5 can be replotted with the gage factor adjustment - either room-temperature or test-temperature - already incorporated. Upon completion, the thermal output read from the replotted curve can be used directly to correct the indicated strain. This procedure may be found worth the effort if many strain readings are to be taken with one gage or a group of gages from the same lot.

For convenience in computerized correction for thermal output, Micro-Measurements supplies, for each lot of A-alloy and K-alloy gages, a regression-fitted (least-squares) polynomial equation representing the thermal output curve for that lot. The polynomial is of the following form:

where:

T = temperature.

If not included directly on the graph, as shown in Fig. 5 , the coefficients for Eq.(504.5 ) can be obtained from Micro-Measurerments on request by specifying the lot number.

It should be borne in mind that the regression-fitted equations, like the data from which they are derived, are based on an instrument gage factor of 2.0; and, for greatest accuracy, the thermal output values calculated from the equations must be adjusted to the gage factor setting of the instrument if other than 2.0. As an alternative, the coefficients in Eq.(504.5) can be multiplied by the ratio 2.0 / , where is the instrument gage factor used for strain measurement. Another consideration which should not be overlooked is that the supplied thermal output data and equations are applicable only to the specified lot of gages, bonded to the identical material used by Micro-Measurements in performing the thermal output tests.

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