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General Description :

• A Thermocouple is a temperature measuring device consisting of two conductors of dissimilar metals or alloys that are connected only at the ends. When the ends are at different temperatures a small voltage is produced in the wire that can be related directly to the temperature difference between the ends. If the temperature at one end is known, the temperature at the other end can be determined.
• Thermocouple cable or extension cable is recommended to be used to connect thermocouples to the sensing or control instrumentation. The conditions of measurement determine the type of thermocouple cable and insulation to be used. Temperature range, environment, insulation requirements, response, and service life should be considered.
• Thermocouple extension cable has approximately the same characteristics as thermocouple cable, but its accuracy is guaranteed over a more limited range of temperatures. Thermocouple extension cable can offer advantages in cost or mechanical properties when used for connections between thermocouple and instruments. For base metal types of thermocouples, extension cable is of substantially the same composition as the corresponding thermocouple type. For precious metal types, however, an entirely different alloy is formulated to match the noble metal characteristics over a specified temperature range. This is necessary due to the high cost of the precious metals, which would otherwise be necessary for the interconnection. The letter X indicates extension cable.
• Compensating cables use completely different alloys that happen to exhibit very similar thermo-electric properties up to a limited temperature (usually 200 °C). Great care should be taken to control the temperature of the junction between the compensating cable and the actual thermocouple material to keep it below the acceptable maximum. Compensating cables come in convenient cabling forms for site installations. The letter C indicates compensation cable.

Table of Alloy Combination :

• Type	Conductor Combinations		Operating Temperature (Continuous)
  	Positive Electrode	Negative Electrode
  KX	Nickel-Chromium (Chromel)	Nickel-Aluminum (Alumel)	0 to 1100 oC
  TX	Copper (Cu)	Copper-Nickel (Constantan)	-185 to 300 oC
  EX	Nickel-Chromium (Chromel)	Copper-Nickel (Constantan)	0 to 800 oC
  JX	Iron (Fe)	Copper-Nickel (Constantan)	0 to 750 oC
  NX	Nicrosil	Nisil	0 to 1200 oC
  BC compensating	Copper (Cu)	Copper (Cu)	0 to 100 oC
  NC compensating	Copper (Cu)	Copper-Nickel (Constantan)	0 to 150 oC
  KCA compensating	Iron (Fe)	Copper-Nickel (Constantan)	0 to 150 oC
  KCB compensating	Copper (Cu)	Copper-Nickel (Constantan)	0 to 100 oC
  RCA/SCA compensating	Copper (Cu)	Copper-Low Value Nikel	0 to 100 oC
  RCB/SCB compensating	Copper (Cu)	Copper-Nickel (Constantan)	0 to 200 oC