Multiple‐Bridge Circuits for Measurement of Small Changes in Resistance Available to Purchase

In the multiple‐bridge circuit, first‐order effects of random resistance variations occurring at the junctions of a Wheatstone bridge are eliminated by an extension of Kelvin's method, which involves adding an auxiliary resistor pair at each bridge corner at which the variations occur. The remaining second‐order error, and the effects of thermals, are evaluated. The multiple‐bridge technique makes possible precise resistance comparisons, and the accurate measurement of small changes in resistance of an element that is connected through switch contacts, or brushes and sliprings. Some numerical design data are given. Elaborations of the basic circuit, and typical applications, including measurements with resistance strain gauges, are described.