What is a thermocouple, extension and compensating cable?

To find temperature ratings we could measure the electrical resistance on metallic conductors (electrical thermometer) or electromotive force (thermocouple). A thermocouple consists in a thermometer itself and the value of the electromotive force (EMF) is determined by the difference between the measuring (or hot) junction and the reference (or cold) junction, which normally is a given temperature (0°C) so that the emf generated depends solely on the temperature of the measuring junction.

Connecting thermocouples

In most cases mineral insulated thermocouples are connected to other measuring instruments by connecting cables. We call these connecting cables extension and compensation cables. The conductors of the cables are available in 2 types: stranded and solid conductors. The main reason to choose for extension and compensation cables are as follows:

  • The basic material is usually lower priced than the mineral insulated thermocouple cable since it does not have to withstand comparable temperatures as the hot end of a thermocouple.
  • The extension and compensation cables have flexible insulation material, so it can easily be installed at sites with many bends.

Conductor Materials

Depending on conductor materials we differentiate temperature measurement cable construction in:

• Thermocouple

• Extension

• Compensating

Cables made of the same material as the original ones are called thermocouple or extension cables. When used to link up the thermocouple with the connection head, whereas cables made of substitutive material are known as compensating cables.

Thermocouple grade

Thermocouple grade means the alloy is exactly the same as the alloy in the temperature sensor and therefore functions similar as a thermocouple.

Insulation and jacket, by ceramic fibre, glassfibre, fluoropolymer, silicone rubber, are suitable for indoor use.

Extension grade

Extension grade compensating cables have the same nominal composition of a thermocouple cable, but are calibrated as class 1 up to 200°C in accordance with DIN 43710. At Kamet, the extension grade cables can be recognized with character x. For example, Kx stands for thermocouple type K extension grade.

Insulation and jacket by fluoropolymers, silicon rubber, thermoplastic compounds, are suitable for indoor and outdoor use.

Compensation grade

Compensating wire and strands are made of alloys that do not have to be identical to the corresponding thermocouple. Substitutive material implies nevertheless that the thermoelectric characteristics have to be the same. They are identified with the letter “C”, according to DIN IEC 60584, placed near the code letter identifying the thermocouple.

Insulation and jacket by fluoropolymer, silicon rubber, thermoplastic compound, are suitable for indoor and outdoor use.

Insulation material

Thermocouple extension and compensation cables are typically insulated with the material listed in below table.

CodeProductMax. Temperature
PVCPVC80°C
PVC HTPVC High temperaturw105°C
XLPE-LS0HHalogen free90°C
GSSilicon180°C
GS HTSilicon High temperature205°C
MFATeflon250°C
PFATeflon260°C
PTFETeflon280°C
PFA HTTeflon300°C
KAPTKapton400°C
TEXGlass fiber type E400°C
TEX HTGlass fiber type R650°C
TEX SHTGlass fiber quartz900°C
CERCeramic fiber1200°C

Read more about the typical insulation materials used for thermocouple extension and compensation cables.