Thermocouple: Principle,working,& types

 

The world is in twenty first century & this era is of technology.Heat is an energy and a fundamental need for lives.In this time of technology advancement every thing is works on specific parameters that's why it is necessary to know accurate values of every input and output.

    Same thing applied in everything where hot work is going to be that is Temperature. To measure the temperature a sensor device is used known as Thermocouple

    Thermocouple is a sensor or device which is used to measure the temperature.

    Now the question arises that temperature can be measured by thermometer or mercury tube But they are used only for limited temperature range. To measure the temperature above and below the range of normal thermometer, thermocouple is used.

    Thermocouple consist of two wires of different conducting (both electricity and heat) material joined in a loop making couple.So thermocouple is a couple made by two wires to measure the temperature.Thermocouple work on principle of Seebeck Effect . Thermocouple are simple and robust temperature sensor to use in measuring of wide range of temperature.When two ends of two different material wire is joined and one end is heated and other is cooled then due to temperature difference a voltage is created and a  small amount of current flows in the circuit and that current is correlated to the temperature.

   Thermocouple is a thermoelectric device because it works on conduction of heat and electricity between wire of two different metal junction. The voltage which developes is proportion to the temperature difference 

Theory behind working of thermocouple::

                         

  Every metal is made up of atoms and atoms have revolving electrons which when takes heat , they continues to flow  they carry heat and electricity as well so metals which conduct electricity they also conducts heat  . This phenomenon is used in thermocouple device works. Heat flows from high temperature to low temperature so election will also move from high temperature to low temperature and if a circuit is made then election will flow in whole circuit making an emf (Electro Motive Force) which can be measured by using multimeter. 

    Thermocouples are mostly used in industrial application in electric arc furnace, chemical industries, air conditioning systems , refrigerator, used to measure the temperature of offices, showrooms,& homes etc.

Types & range of thermocouple::

                            Thermocouples are mostly used in industries and scientific research work due to their accuracy and large  operation range .They are classified on the basis of application, temperature range to be measured, chemical properties of work environment,stability , availability and cost . According to these points, thermocouples are of 10 types that are :

1. Type B thermocouple [up to 1800 ℃]

2. Type C thermocouple

3. Type E thermocouple[-200℃ to 900℃ ( -328°F to 1652°F)]

4. Type J thermocouple [-210 ℃ to 750℃(346°F to 1400°F)]

5. Type K thermocouple [-200℃ to 1250 ℃ (-328°F to 2282°F)]

6. Type N thermocouple[-270℃ to 1300 ℃]

7. Type R thermocouple [0 ℃ to 1600 ℃ ]

8. Type S thermocouple [630 ℃ to 1064 ℃]

9. Type T thermocouple [-250℃ to 350℃ ( -418 °F to 662 °F)]

10. Tungsten & tungsten rhenium thermocouple