What is a thermocouple cable?
Thermocouple cables are used to extend thermocouple signals to associated instrumentation. Depending on the grade they can also be used to make a thermocouple sensor such as a simple welded tip thermocouple.
Thermocouple cables are available in a variety of sizes and number of strands. In general solid comductors are better for making thermocouples and stranded, more flexible cables are more suited to extending thermocouples. They are supplied with PVC, PFA, fibreglass or ceramic fibre insulation - each insulation has its own merits, but the overriding characteristic is the different temperature ratings for each insulation material.
Thermocouple cables are available as single pair thermocouple cables and multipair thermocouple cables where up to 24 thermocouple pairs are in a single cable. They are colour coded according to the thermocouple type; green for type K, brown for type T, black for type J etc., as defined under IEC60584.3. Full colour codes for thermocouple cables are shown here.
For more detailed technical information on thermocouple cables, colours, specifications and tolerances, why not request our free guide to thermocouple and resistance thermometry?
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What is the difference between extension wire and compensating cable?
Extension cables have conductors which are the same as the thermocouple type itself. For example a Type K extension cable (KX) will have NiCR/NiAl conductors whereas a Type K compensating cable (KCB) has Cu/Con conductors. Compensating cables are made using less expensive conductor materials (particularly important for Type R and S thermocouples) that exhibit the same thermoelectric properties as the thermocouple type, provided that the join of compensating to thermocouple material is kept within certain temperature limits (0ºC to 80ºC and usually around ambient for all practical purposes).
Thermocouple cables are available in different constructions from simple 'bell wire' style to complex multi-pair constructions where thermocouple pairs are individually screened, collectively screened with tapes and steel wire armouring.
Cables with twisted cores provide protection against electromagnetic interference and screening rejects electrostatic interference. Cables are available with a stainless steel braid for mechanical protection and some cables are available with a steel wire armouring.
Flat twin cables are a good general purpose choice for extending thermocouples back to instrumentation. Most of our cables are suitable for connecting to miniature or standard thermocouple connectors.
What colours are thermocouple cables?
In the UK and Europe, thermocouple cable colours are usually to IEC 60584-3 and are commonly referred to as 'IEC colours'.
In the USA and Australia, ANSI colour codes are more prevalent and these are shown in the table below alongside the colour codes for the most popular thermocouples in the UK according to IEC 60584-3.