In most cases thermocouples are connected to other process instruments by connecting cables. Connecting cables are divided into compensating cables and extension cables. These can again be divided into solid and stranded conductors.
Extension cables are connecting cables with conductors made of thermocouple material, i.e. of the same material as the thermocouple itself. Extension cables therefore are subject to the same accuracy limits as the thermocouples. Extension cables are marked with an „X“ behind the identification letter for the thermocouple. For example, „KX“ means that the cable is an extension cable / insulated thermocouple wire for the thermocouple type K (NiCr-Ni).
Compensation cables are connecting cables with conductors made of materials which only in a limited temperature range have the same thermoelectric properties as the thermocouple itself. Compensating cables are marked with a „C“ behind the identification letter for the thermocouple. For example, „KC“ means that the cable is a compensating cable for the thermocouple type K.
The insulation of the conductors as well as of the sheaths can be made of a variety of materials. The following criteria must be taken into consideration when selecting the appropriate material: chemical and mechanical resistance against the ambient conditions, temperature range, insulation resistance, flexibility, outside diameter, screening etc.
Apart from that there is a great number of cable types available as compensating cables or extension cables as well as those with more than two inner conductors. Many special designs are available upon request, some of them on a short term basis.