Errors in Shunt Calibration of Strain Gauge Circuits Due to Cable Resistance

摘要

Strain gauge installations in naval vessels require long cable lengths between strain gauge sites and the strain measuring instrumentation due to the size of the vessels and the complexity of the cable runs. The resistance of the signal cable can cause an attenuation error during the acquisition of strain data. This error can be compensated for by performing a shunt calibration directly on each active strain gauge. However often the strain gauges are inaccessible after installation, in which case the shunt calibration is performed at another part of the Wheatstone bridge or at the instrumentation. The long cable runs can also cause errors in the calibration if it is not undertaken across the strain gauge. The attenuation errors and the calibration errors are additive and in a typical naval vessel installation can result in a total error of up to 20% of the strain signal. This paper contains derivations of exact formulae for the correction of these errors for various wiring configurations. The more complex formulae were simplified by practical approximations but still retained an accuracy of at least 99% of the exact solutions. It has also been mathematically demonstrated that the use of higher resistance strain gauges reduces the strain errors due to cable resistance. The derived theoretical solutions have been verified by practical experiments for some of the wiring configurations.