Examining Theory of Thermocouples

A thermocouple is an electrical device including two dissimilar electrical conductors forming electrical junctions at differing temperatures.

A thermocouple generates a temperature dependent voltage as a consequence of thermoelectric effect.

In simple words, a Thermocouple is a device used for measuring temperature. It determines temperature in the form of an Electric current or the EMF.

A thermocouple is mainly made up of Nickel alloy, platinum or rhodium alloy, Tungsten or rhenium alloy, chrome-gold, and iron alloy.

How does a Thermocouple function?

  The working of a thermocouple is entirely bases on three effects.

  • See back effect: The see back effect happens between two different metals. So whenever there is heat given to any one of the metal then the electrons starts flowing from hot metal to cold metal. As a result, direct current moves in the circuit. In brief, it occurs when the temperature difference between two metals moves the potential difference between them.
  • Peltier Effect: The Peltier Effect is completely reverse of the See back effect. This effect defines that the temperature variation can be built between any two different conductors by using the potential difference between them.
  • Thompson effect: The Thompson effect means that when two different metals combine together and if they build two junctions then the voltage induces the full length of the conductor due to the temperature gradient. The temperature gradient means the direction and rate of change of temperature at a particular location.

Working of a thermocouple

The circuit of a thermocouple includes two dissimilar metals. These metals are configured in such a way that they create two junctions. The metals are then wedded to the junction. if the temperature at the junction gets equal then the equal and opposite EMF gets generated in the circuit. As a result Zero current starts flowing through it. The magnitude of EMF is directly dependent on the type of materials used in building a thermocouple.

Measuring Thermocouple output

  • Multimeter: It is preferred as the simplest way of measuring the output of EMF of the thermocouple. The Multimeter is always linked to the cold junctions of the thermocouple. The deflection of the Multimeter pointer is directly proportional to the current flowing through the meter.
  • Amplifier with output devices: With the help of an amplifier, the output generated from the thermocouples is amplified. And then the output is feed either in the recording or in indicating instrument.
  • Potentiometer: The DC Potentiometer can also assist in measuring the output of the thermocouple.

Advantages of a thermocouple

There are some major advantages of a thermocouple. They are listed below.

  • Thermocouples are economical. They are much cheaper than the other devices used for measuring temperature.
  • Thermocouple has an ability of fast response time
  • It includes a wide temperature range.

Disadvantages of a thermocouple

There are some disadvantages too. Few of them are listed below.

  • The recalibration in case of a thermocouple is really difficult.
  • A thermocouple has low accuracy.