Null detector

A null detectors is an electrical measurement instrument used to measure minute voltages. High precision null detectors can resolve voltage differences in the nanovolt range. Null detectors are typically designed to have high input impedance to minimize loading the circuit under test.

Null detectors have historically used in calibration laboratories in conjunction with Kelvin–Varley dividers and bridge measurement circuits. Because of their sensitivity and specialized operating range, null detectors were more commonly used in laboratory than in routine field measurements. They were used as part of measurement chains that established traceability to national electrical standards, such as those maintained by National Institute of Standards and Technology (NIST).