It should be noted that the instrument gage factor setting employed in recording thermal output data is standardized at 2.0 for all Micro-Measurements A- and K- alloy gages. If, during strain measurement, the user's instrument is set at a gage factor different from 2.0, the thermal output component of the indicated strain will differ accordingly from that given in Fig. 5 . This difference is usually no more than several percent when the instrument gage factor is set to that of an A- or K-alloy gage. A modest improvement in the accuracy of the thermal output correction can thus be made by adjusting the data from Fig. 5 (taken at = 2.0) to the current gage factor setting of the instrument. This is done as follows:

   Eq.(504.4)

where:

= thermal output adjusted for instrument gage factor setting.
= thermal output from gage package data sheet ( = 2.0).
= instrument gage factor setting during strain measurement.

Continuing the numerical example, and assuming that the data sheet gives a room-temperature gage factor of 2.10 for the gage, and that the instrument is set at this same gage factor, the adjusted thermal output is calculated from Eq.(504.4):

And the corrected strain measurements become:

and

As shown in Fig. 5 , the gage factor of the strain gage varies slightly with temperature. When this effect is significant relative to the required accuracy in strain measurement, the gage factor of the strain gage can be corrected to its test-temperature value, and the gage factor of the instrument set accordingly. The resulting instrument gage factor is substituted into Eq.(504.4) to obtain the adjusted thermal output, which is then subtracted algebraically from the indicated strain to yield the stress-induced strain.

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