chapter  3
Operational Modes of Instrumentation
Pages 8

A null instrument o¥ers certain intrinsic advantages over other modes of operation (e.g., see dežection instruments). By balancing the unknown input against a known standard input, the null method minimizes interaction between the measuring system and the measurand. As each input comes from aseparate source, the signiŸcance of any measuring inžuence on the measurand by the measurement process is reduced. In e¥ect, the measured system sees a very high input impedance, thereby minimizing loading errors. œis is particularly e¥ective when the measurand is a very small value. Hence, the null operation can achieve a high accuracy for small input values and with a low loading error. In practice, the null instrument will not achieve perfect parity due to the usable resolution of the balance and detection methods, but this is limited only by the state of the art of the circuit or scheme being employed.