ABSTRACT
Classical electrical instrumentation and measurements systems often made use of null measurement systems. The Kelvin bridge is a specialized circuit used to measure very low resistances, such as ammeter shunts and motor armatures. Null-based measurements were seen to not rely on meter accuracy, only meter sensitivity, which was available. The accuracy of a DC null measurement system is derived from the known, calibrated accuracy of the resistors making up the bridges or potentiometer and has little dependence on the analog null meter. Potentiometers were used with thermocouples to obtain precise temperature measurements and in electrochemistry laboratories to measure cell electromotive forces. The chapter describes how the Anderson loop works and discusses its benefits and shortcomings, comparing it with circuits as the traditional, voltage-excited, Wheatstone bridge. Wheatstone bridges are traditionally used to make precise, accurate resistance measurements or to measure some physical quantity, such as temperature, light intensity, or strain, which causes a known change in resistance.
