What Are Thermocouple Extension/Compensating cables?
What Are Thermocouple Extension/Compensating cables?
When it comes to thermocouple cables, there is a lot of confusion about the terms "thermocouple extension cable" and thermocouple compensating cable." These types of cables are used for different goals in a thermocouple. Read this blog to find out the differences.
What Is A Thermocouple Extension Cable?
When it comes to thermocouple wire, there are two ways to define a thermocouple extension cable. In the first case, it is just another name for the actual thermocouple cable. Type K, Type J, Type T, Type N, Type E, and other subtypes of a thermocouple wire are all called thermocouple extension cables.
Another way to define a thermocouple extension cable is by stating that it is a thermocouple cable used for extension purposes only. In this case, the cable is defined by the letter X, which means extension. For the thermocouple cable K, the corresponding extension cable is KX. For the thermocouple cable T, it is TX. While this cable is used for the extension of the thermocouple cable, it is made from the same materials as the true thermocouple wire. The temperature range of the thermocouple extension cable is up to 200°C. The cable follows the DIN 43710 standard.
Most true thermocouple cables can be extended with thermocouple extension wire. Exceptions are type B, type R, and type C thermocouples. The reason why they cannot be extended is that they contain precious metals like rhodium and platinum, which makes them too expensive to extend.
What is a Thermocouple Compensating Cable?
A compensating cable is an additional thermocouple cable that is used to extend the signal of the true thermocouple wire. It brings the signal from the sensor to the instrumentation.
A thermocouple compensation cable is not made with the same instruments as a more expensive true thermocouple wire, such as nickel-chromium and nickel-alumel for Type K or iron and constantan for type J. The alloys that are used for compensating cables are way cheaper.
While the materials are not the same, they emulate certain characteristics of a true thermocouple cable. Namely, it is the relationship between the temperature of the cable and the value of the electromotive force (EMF).
Unlike true thermocouple wires, compensating cables only operate in ambient temperatures. They commonly have PVC insulation that is known to limit the temperature range. Depending on the cable, the operating temperature could be anywhere up to +200 C, with the range between 0 up to +200 °C. With compensating cables, you would never see operating temperatures of +1000 C or +2000 C. In fact, they do not reach the temperature range of any type of true thermocouple wire.
What is more, compensating cables are not nearly as accurate as the true thermocouple wire. They follow the designated standard DIN IEC 60584.
Why Would I Use A Compensating Cable?
Price is the main reason to use compensating cables. They are considerably cheaper than the thermocouple wire, so it makes sense to use them to connect the sensor to the instrumentation, as it would save a considerable amount of money. Type X extension cables are also cheaper than true thermocouple wire because of the smaller temperature range.
What Are The Available Compensating Cables?
Compensating cables on the market have the name CA, which stands for "compensating alloy." All popular thermocouple wires have a compensating cable analog. The analog of type K would have the name "KCA," while the analog of type J goes under the name "JCA."
At Nassau National Cable, we sell widely used true thermocouple cables on the market and thermocouple extension cables, including Type JX, Type EX, Type TX, Type K, Type TX, and Type J.
