This note gives test results which show that the' out-of-balance current in a Wheatstone bridge consisting of four unstrained resistance strain gauges increases at first sensibly in proportion to the applied bridge voltage, i.e. the current through the gauges. This is as expected. Then as the gauge current increases the out-of-balance current departs appreciably from this linear law by an amount approximately proportional to the cube of the gauge current. Any errors in resistance -compensation against temperature changes between gauge and gauge might be expected to increase with the current squared, and the consequent out-of-balance current in the galvanometer due to this effect as the current cubed. This is probably the explanation of the effect found.nDue to the presence of this effect in strain gauge installations, null point methods of measuring bridge out-of-balance due to strain will be inaccurate at high gauge currents unless the current is kept constant. The advantage of the null point method in that the result is independent of the applied voltage, is thus lost.
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