When taking connection from a Thermocouple to Instruments which are some distance away, either by permanent wiring or flexible cable, it is essentials to use materials having the same EMF output as the Thermocouple combination else spurious EMF can be generated at the junctions.

The best solution is to use leads of the same alloys as the Thermocouple. These are usually called Extension leads and are supplied as “Extension lead quality”, normally reffered to as KX, JX, TX, AND EX. Where this solution would be too expensive, comparatively cheaper alloys of different types from the Thermocouple combinations are used. These combinations have an EMF matched as closely as possible to the Thermocouple alloys although the EMF of the individual legs is not usually the same.

These Materials are termed as Compensating leads and generally give adequate compensation for EMF’s generation junctions. Compensating cables have, within a limited temprature range, the same Thermo Electric characteristics as the actual Thermocouple wires. Therefore, by using such cables to interconnect between the Thermocouple connection head and the measuring instruments or cold junction compensators, the cold junction is relocated at the measuring instruments or cold junction compensators.

Colour Code chart (click image to enlarge)