A practical industrial or laboratory Thermocouple consists of only a single (measuring) junction; the reference is always the terminal temperature.
Possible measures are:
- Measures the terminal temperature accurately and compensate accordingly in calculating the measured value.
- Locate the terminals in a thermally controlled enclosure.
- Terminate not in copper cable but use compensating or actual thermocouple wire to extend the sensor termination to the associated instrumentation (compensating cable uses low cost alloys, which have similar thermoelectric properties to the actual thermo element). On this basis, there is no thermal voltage at the thermocouple termination. The transition to copper then occurs only at the instrument terminals where the ambient temperature can measure by the instrument; the reference junction can then be compensated for electronically.
- Use a temperature transmitter at the termination point. This is effectively bringing instrumentationclose to the sensor where electronic reference junction techniques can be utilized. However, this technique is convenient and often used in plant; transmitter produces an amplified (corrected) signal, which can be sent to remote instruments via copper cable of any length.
