Thermocouple Instrument

a device used to measure the strength of alternating current and, less often, voltage and power.

A thermocouple instrument is a combination of a permanent-magnet instrument and one or more thermopiles. The thermopile consists of a thermocouple (or several thermocouples) and a heater, through which flows the current to be measured. Under the action of heat released by the heater, a thermal electromotive force (emf) is generated between the free ends of the thermocouple and is measured by the permanent-magnet instrument. For currents of 1 ampere and higher, high-frequency instrument current transformers are used to expand the measurement limits of the thermopiles.

Thermocouple instruments provide relatively high measurement accuracy over a broad frequency; the accuracy does not depend on the shape of the curve of the current flowing through the heater. Their main disadvantages are the dependence of the readings on the ambient temperature, their significant power consumption, and their intolerance of large overloads (greater than a factor of 1.5).

Thermocouple instruments are used primarily for measuring the effective value of the strength of alternating current (from microamperes to several tens of amperes) in the frequency range from several tens of hertz to several hundred megahertz, with an error of 1–5 percent.