What is a thermocouple? How do they work?

A thermocouple is a device for measuring temperature. It comprises two dissimilar metallic wires joined together to form a junction. When the junction is heated or cooled, a small voltage is generated in the electrical circuit of the thermocouple which can be measured, and this corresponds to temperature.

In theory, any two metals can be used to make a thermocouple but in practice, there are a fixed number of types that are commonly used. They have been developed to give improved linearity and accuracy and comprise specially developed alloys.

Thermocouples can be made to suit almost any application. They can be made to be robust, fast responding and to measure a very wide temperature range.

View our range of thermocouples

A title

Image Box text

Do you require a thermocouple for your application?

Our Thermocouple range

What does a thermocouple do?

A thermocouple is simply a sensor that is used for measuring temperature. This design of sensor consists of two dissimilar metal wires which are joined together at one end, connected to an instrument that is capable of accepting a thermocouple input and measure the reading. Thermocouples can provide temperature measurements over a wide spectrum of temperatures dependent on which thermocouple type you use.

Discover our range of thermocouple sensors
a thermocouple sensor against a white background - this measures temperature using a cross-junction of two different metals.

Example of a Thermocouple manufactured by Process Parameters

a 2D diagram showing from Process Parameters showing a small and a medium thermocouple sensor with two pins and how they work

Thermocouple diagram

Thermocouple Working Principle

A thermocouple is a temperature measurement device that operates based on the principle of the Seebeck effect. Thomas Seebeck discovered the continuous current flow in the thermoelectric circuit in 1821. It consists of two different types of metal wires or conductors that are joined at one end to form a junction. When this junction is exposed to a temperature gradient (a difference in temperature between the two ends), it generates a voltage that is proportional to the temperature difference. This voltage is called the thermoelectric voltage.

Types of Thermocouple Temperature Sensors

Thermocouple probe

What is a thermocouple probe?

What is the definition of a thermocouple? Now we have an understanding of how a thermocouple works and what thermocouples are, one of the popular questions is what is a thermocouple probe?

A thermocouple probe is the design of the sensor that it is made in. Whether the sensor is a thermocouple type K, J, T, N all of these thermocouple types can be manufactured in the same size tube, housing or construction. To get an idea of the typical design available check out some of our thermocouple sensors.

What does a thermocouple look like? Thermocouples look different due to the constructions they are manufactured in. Although a thermocouple itself is two bare wires joined together, these two wires can be put inside various constructions to protect them so they last longer.

What is a type K thermocouple?

A popular question asked is what is a type K thermocouple?

A type K Thermocouple is made up of two dissimilar metals which are Nickel-Chromium / Nickel-Alumel. Type K is the most popular type of thermocouple because it is inexpensive, accurate, reliable (depending on the design used for your application) and covers a wide temperature range.

Type K thermocouples can be found in a broad range of applications due to its expansive temperature range capabilities. The maximum continuous temperature is up to around 1100 Deg C.

Thermocouples with a plug or cable can be identified by their colour coding. In this case type K is green. If you have a cable the green leg is positive and the white leg is negative.

A Process Parameters Type K thermocouple made from Nickel-Chromium or Nickel-Alumel with green casing.

Type K Thermocouple

What is a type J thermocouple?

So what is a type J thermocouple? Type J Thermocouples are also very common. It has a smaller temperature range than a type K thermocouples with a range of 0 to 600 Deg C. The Type J is made up of two dissimilar metals which are Iron / Copper-Nickel (Also known as Constantan). Cost-wise they are very similar to type K.

One of the most popular applications you find type J being used is in the plastics industry.

Thermocouples with a plug or cable can be identified by their colour coding. In this case type J is Black. If you have a cable, the black leg is positive and the white leg is negative.

A Process Parameters type J thermocouple made from Iron / Copper-Nickel (aka Constantin) with black casing.

Type J Thermocouple

Looking for a thermocouple for your application, or not sure what you need?

More About Thermocouples