The measurement of temperature is becoming important in many fields of activity. The needs of better techniques and improved accuracy is also constantly present.

Extension cables are a convenient and frequently economic way of extending thermocouple circuits from the sensor to the reference unit in the form of wiring cables with similar conductor materials to those of the sensor. Alternatively they may incorporate quite different conductor (alloys) materials which in combination develop similar out puts to be experienced at the thermocouple to extension wire connections, where ever compensating cables are having cheaper alloys of different types in combination match the thermocouple characteristics as closely as possible, but over a limit temperature ranges.

An obvious example of the use of compensating cables is with platinum. Metal thermocouple where the cost of the thermocouple materials is high and it is usually an economic necessity to extends the circuits using lower cost compensating cables, however if the temperature of the connecting box is allowed to increase the out put from the compensating wire will be diverge from that of the platinum thermocouple and errors in the temperature determination will increase correspondingly.

Another example of the use of compensating cables is where the output of 'K' type thermocouples is closely matched at low temperatures by the combinations of Cu/Cu-Ni alloys. As one conductor is already copper the number of reference junctions is halved, an advantage with large multi-thermocouple schemes. The loop resistance of this cables is also same what less than with the equivalents 'K' type thermocouple alloys. Extension cables are produced usually in a convenient form for carrying over long distances e.g. as wire cables or multi-core cables, with extension cables this mismatch errors arising from high connecting box temperature are likely to be less than with compensating cables.

Note : These cables are available in various insulations i.e. PVC, HR-PVC, FRLS-PVC, Fiber Glass, PTFE (Teflon) & Rubber Compound.