What Is a Thermocouple Compensation Cable?

March 22, 2021 Sascha Mais

Where are thermocouple compensation cable used?

thermocouple compensation cable is the connection between a thermocouple and a measuring device. The cable must be made of the same materials as the thermocouple; otherwise, the measurement would be falsified due to unwanted additional thermal voltages. This is also called the Seebeck effect. The materials of the cable must be matched to the respective thermocouple type.

We find a typical application example for the use of thermocouples in injection molding machines, for example. During the manufacturing process of plastic parts, the temperature in the machines must be constantly monitored. This task is carried out by thermocouples.

In the injection molding machines in the photo to the left, thermocouples are used for temperature monitoring.

What is a thermocouple?

Thermocouples are widely used in industry to measure temperatures beyond 200°C. In the simplest case, an electronic temperature measuring device consists of two components: a thermocouple as a measuring transducer and a measuring device.

How does a thermocouple work?

A thermocouple consists of two wires made of different metals. These are connected to one another at one end. In industrial applications, these are usually welded together because this gives them a high level of vibration resistance.

A measuring device is connected to the open end of the two metals. This processes the signals from the thermocouple. Due to the thermoelectric effect, a voltage can be measured between the two unconnected ends. If the temperature at the measuring point rises or falls, the electron density of the two metals changes. This changed electron density can be measured as a changed voltage at the wire ends.

Who invented it?

The thermoelectric effect occurs due to the change in temperature. It is also known as the Seebeck effect. Thomas Johann Seebeck was a German physicist who was the first to document this effect in 1821.

The two most common types of thermocouples

It is important to know that all thermocouples are subject to an aging process. In this case, one speaks of a drift. This aging process is irreversible and cannot be predicted. As a result, the measurements become less accurate over time. 

There are different types of thermocouples. The various metal pairings and their measurement accuracy are specified in IEC standard 60584.

I would like to briefly introduce the two most frequently used types at this point.

Thermocouple type K:

NiCr - Ni 

Consists of: nickel - chromium alloy / nickel

Temperature range: -40°F to 2,192°F

IEC color code: green - white

Thermocouple type J:

Fe - CuNi

Consists of: iron / copper - nickel alloy

Temperature range: -40°F to 1,382°F

IEC color code: black - white

Thermal compensation cables designed for use inside cable carriers

For applications with cable carriers, there is the CFTHERMO series of chainflex® cables. These thermal compensation cables meet all the properties required of a thermal compensation cable according to the IEC standard.

chainflex® cables are subjected to numerous tests inside our test laboratory at our headquarters in Cologne, Germany. For example, the CFTHERMO.K.001 successfully withstood more than 97 million strokes in a cable carrier test.

We've seen thermal compensation cables used in e-chains® in plastic welding machines, among other things. Here, the temperature at the welding tip must be closely monitored. If this temperature is too low, the workpieces cannot be connected to one another completely or even at all. If the temperature is too high, there is a risk that the workpieces will be deformed or damaged.

Visit our webpage to learn more about chainflex® thermal compensation cables. You can also contact an igus® expert here with any questions. 

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