Thermocouple Cable

Compensating cable is generally copper based conductors which may produce unreliable outputs for most application and is generally a cheaper method of providing cabling from the measuring point to the instrumentation.

Extension cable is thermocouple material conductors which on most occasions will provide continuity of thermocouple circuit and reliable data depending on the manufacturing processes involved in constructing a thermocouple assembly with cable.
-from http://www.universal-thermosensors.co.uk/cables/extension-cables.htm

Thermocouple extension cables, are cables with conductors equal material of thermocouple or thermopar sensor (J, K , E type). These extension cables are designed to carry signal from sensor to transmiter or monitor, when the mounting is separate, no is integrated sensor-transmitter on one unit.

Compensating cable are for RTD sensor, is the third conductor of one triad cable for RTD signals, for compensanting of the resistance (ohms) what have for the distance among RTD sensor and monitor or transmitter until Wheastone bridge circuit.

As All-For M.E compensating cable is copper based and cheaper than thermocouples extension wire.

If you use compensating cable, you must calibrate your reading/recording equipment with the exact length of wire you will be using.

If you use a multi-point recorder then all cables would have to be the same length.

You get an error every time you use a different material. That applies to the cables and the connectors. A "perfect" system will use a continuous thermocouple wires from test location to recorder. As soon as you deviate from this you add measurements errors. Unfortunately, thermocouple wire is more expensive than standard copper wire or various recipe in between.

This is a typical engineering dilemma. You have to choose between cost and precision. How much does a 5% measurement error cost you? Is it more than a full length thermocouple wires?