Thermocouple

Connecting the thermocouple sensor to instrumentation must be done carefully to optimize accuracy and minimize cost. The resultant temperature measurement is only as accurate as the sensor and its interface.

The thermocouple produces only a small thermo-electric e.m.f (typically 40μV/oC) and it is necessary to eliminate or minimize spurious thermal emf signals and Ohmic effects which would otherwise result in incorrect readings.

The length of cable used between the sensor and the instrument is an important consideration because the line resistance has to be taken into account (although the instrument input is effectively high impedance, the input usually incorporates special circuitry to result in an ‘upscale’ reading in the event of sensor failure).