How Does a Thermocouple Work?

How Does a Thermocouple Work?

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Introduction of Thermocouple

Thermocouples are the most common sensors which are used for the measurement of temperature. Made of two different metals being coupled together at one or more than one point. The thermocouple features the voltage production if there is any temperature between the temperature of one of the points and the reference temperature.

Thus, the thermocouple measures the unknown temperature of one body to the known temperature of the other body.

Working Principle of Thermocouple

The working principle of the thermocouple is based on three effects. These effects, discovered by Seebeck, Peltier, and Thomson are as follows:

Seebeck Effect

The Seebeck Effect states that an electromotive force is generated at the junction when two different metals are joined with each other at the junction. It’s the combination of the metals, which decides the amount of emf generated.

Peltier Effect

The Peltier Effect states that when the dissimilar metals are joined together in order to form two junctions, an emf is generated within the circuit. This is due to the difference in temperature of the two junctions in the circuit.

Thomson Effect

According to the Thomson effect, when two, unlike metals, are joined in such a way that a junction is formed, the potential is generated within the circuit due to a temperature gradient, which gets generated along the entire length of the conductors.

Overall, the working principle of the thermocouple is primarily based on the Peltier effect.

The thermocouple circuit in a thermocouple features two metals, which are joined together in order to form two junctions of varied temperatures.

Due to the difference in the temperatures of both the junctions, a Peltier emf is generated. This generated emf within the circuit can be measured based on the temperature of the junctions and depend upon the properties of metals used in the circuit.

In an attempt to the measurement of the temperature through Thermocouple, a body of unknown temperature connects to either of the junctions of the thermocouple circuit. This junction is known as the hot junction.

The body, whose temperature is known, is connected to the other junction, which is known as the cold or reference junction. To measure the voltage/current output from the thermocouple, a voltmeter is connected to the circuit of the thermocouple, which measures the amount directly.

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Applications of the thermocouple

The thermocouple is being used in the following application areas:

  • In food industry for low temperature and cryogenic applications
  • In Iron, steel and aluminum industries for monitoring of temperatures of metals
  • In Petroleum refineries and chemical plants for testing temperatures of process plants
  • In gas appliances for sensing pilot flame
  • For the purpose of measuring incident infrared radiation.
  • Performing like a heat pump in order to deliver thermoelectric cooling

Advantages of the thermocouple

There are several advantages of the thermocouple, which are listed as follows:

  • Higher accuracy in the measurement
  • Robust in nature
  • Fast thermal response
  • Wide range of the temperature measurement
  • Low priced product
  • Higher reliability

Thermocouples are mainly used in the Science and other industries and since they are accurate in nature and bear the wide range of temperature measurement capability, the thermocouples are really an interesting device to work with.

The working scenario of the Thermocouples makes it useful for making an automated measurement and provides an easy approach towards the temperature measurement. Being an inexpensive device to work along with the durability, the thermocouples are the best device for the purpose.

A thermocouple can measure both higher and lower temperatures in comparison to a standard temperature sensor. The features like low cost and durability make it well suited to industrial applications, which includes OEM, oil and gas, BioTech, pharmaceutical and many others.

They are also available in many household appliances such as toasters, stoves, and furnaces.  

Make a choice of the perfect thermocouple based on your needs. Depending on the needs, there are various thermocouples which are suited for a variety of needs and demands of the working. You need to make a choice of the perfect one, depending on your needs.

Remember that the thermocouple performs its work through a thermoelectric effect.


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