What do you need to know about compensating and extension wires for Type C and D?

Extension wires are generally the same alloy as the thermocouple itself. They connect the thermocouple to the instrumentation for transmission of the readings.

In some setups, the extension wire passes through less hazardous environments that are also at a lower temperature than the sensor. In these cases a different extension wire can be used, one that is made of cheaper materials. This is called a compensating wire and can be of interest for Type C and D thermocouple because they are composed of  exotic and thus expensive metals. Compensating wires can therefore provide significant cost savings. However, there are even more reasons that make compensating wires interesting to consider:

• Type C and Type D wires are fragile while compensating wires are more resistant to breaking through flexing, vibration or mechanical strain
• Compensating wires can also offer good resistance to oxidation which is a specific weakness of Type C and D wires.

Kamet can supply nickel based alloys 405 and 426 as compensating extension wires for the Type C thermocouple. They have a base metal composition and are stable with excellent oxidation resistance and ductility. Furthermore, alloys 405 and 426 are suited to temperatures from 0ºC up to 870ºC.

Compensation wires for Type D thermocouples are significantly more limited. They are available as a copper based alloy which can only be used up to 200ºC. Furthermore, copper does not offer the oxidation resistance of the 405 and 426 alloys. Contact the inhouse specialists at Kamet, they can advise you on workarounds in using compensation extensions for Type D thermocouples.

For products relating to Type C and D thermocouples please contact our sales department. They are happy to help with you project needs.