Compensating Cables

These cables form part of the every industry and are used as accessories to temp. measuring instruments. Thermocouple used for industry application are normally not connected to the measuring instrument, generally the thermocouple wires are round from the measuring point to the terminal of electrical thermometer. The extension wire is not used in temp. range above 200°C it has to show the thermoelectric voltage of the thermocouple only upto 200°C.
The extension leads, for noble metal thermocouple as PtRh-Ptstr made of special cheaper material. Through the composition of these special materials doesnot correspond to that of the thermocouple itself yet the thermoelectric voltage is same in a temp range upto 200°C. Such extension leads are called compensating extension wire.
According to ANSI, letter 'X' follow the code letter of thermocouple to represent the extension/compensating wire of respective thermocouple. The type designation of thermocouple and materials of extension/compensating wires are as under :

Extension /compensating wire cables are manufactured in different construction as per customer's requirement using thermoplastic/elastomeric or fluroplastic material as dielectric. However, the most common constructionnormally sought by customer is as under :

1) Conductor - Pair of wires depending on the type thermocouple for which it is to be used
2) Insulation - P V C
3) Pairing - +Ve and -Ve wires twisted together to form pair
4) Individual Pair shield-aluminium backed mylar tape with min 25% overlap and in contact with drain wire
5) Bundling - Pairs laid up together and lapped with polyster tape
6) Collective shield - Aluminium backed mylar tape with min 25% overlap and in contact with drain wire
7) Inner Sheath - PVC
8) Armouring - Galvanized round steel wire/flat strip armouring
9) Outer Sheath - PVC outer sheath may have additional FR(flame retandant / FRLS(flame retardant low smoke) properties
10) Ref. STD. Gen. to IS-1554/1/88 and IS-8784/87