Remedial Measures

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One simple method of reducing all imbalances and errors is to reduce the ratio . This can be accomplished by using higher resistance gages when available.

The many problems of a single common leadwire as outlined above can be totally eliminated by using Micro-Measurements Bridge Completion Modules to move dummy resistors to the gage site, and employing common leadwires for all parallel circuits to both positive and negative terminals of the power supply. For this technique to be effective, both common leadwires must have the same resistance and be subjected to the same changes in temperature. The relatively minor problem of leadwire desensitization remains but this can be eliminated by shunt calibrating the active or dummy gages. Unfortunately, additional wires are required for remote shunting.

Summary

The use of a common power-supply leadwire can introduce large errors in strain measurements, along with practical instrumentation problems such as excessive initial imbalance. Unless absolutely necessary, the common power-supply leadwire should be avoided altogether. When a common leadwire must be employed, the user needs to be aware of the error magnitudes, and should always take steps to minimize these errors through selection of the proper leadwire size and, whenever practical, through numerical correction of measured data.

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