Shunt Calibration of Strain Gage Instrumentation

The need for calibration arises frequently in the use of strain gage instrumentation. Periodic calibration is required, of course, to assure the accuracy and/or linearity of the instrument itself. More often, calibration is necessary to scale the instrument sensitivity (by adjusting gage factor or gain) in order that the registered output correspond conveniently and accurately to some predetermined input. An example of the latter situation occurs when a strain gage installation is remote from the instrument, with measurable signal attenuation due to leadwire resistance. In this case, calibration is used to adjust the sensitivity of the instrument so that it properly registers the strain signal produced by the gage. Calibration is also used to set the output of any auxiliary indicating or recording device (oscillograph, computer display, etc.) to a convenient scale factor in terms of the applied strain.