Extension cable is a type of thermocouple cable that is used to create thermocouple temperature sensors. Extension cable is made from standardised thermocouple alloys. Different dissimilar alloys are paired together to create the standard thermocouple types. Different thermocouple types are suited to different applications as they each have a different temperature ranges and sensitivities. Extension cables are designated with the thermocouple type and the letter X, so Type K extension cable is called Kx.
See also: Compensating cable