chapter  4
20 Pages

DC Null Measurements

The DC null techniques are used with Wheatstone bridges, Kelvin bridges and potentiometers to obtain increased measurement accuracy based on the fact that the human observer can estimate the occurrence of a dc null on a null meter with greater precision than can be read directly from the meter scale in volts. 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 null meter. The human eye is quite sensitive in detecting the microscopic, transient deflections of the pointer of an analog null meter under non-null conditions.