Thermocouple type instrument

Thermocouple instrument

In this article, we discuss a thermocouple instrument. Like hotwire instrument, a thermocouple instrument is also a type of electrothermal instrument.

What is a thermocouple instrument?

When two-conductor of different elements are joined together, a voltage is generated at the joining point (known as junction) which is proportional to the temperature. That junction is called a thermocouple.

So, the instrument having a thermocouple in it is called a thermocouple instrument.

This principle is used to convert heat energy into electrical energy at the junction. The heat produced at the junction is generated by an electrical current flowing in the heating element and the thermocouple produces an emf at its output terminal. The output can be measured with the help of the PMMC instrument.

Construction of thermocouple instrument

A thermocouple instrument includes a heater element and a thermoelement with a PMMC instrument. The circuit diagram of the thermocouple instrument is shown below:

Diagram of thermocouple type instrument.
On the left side (blue color wire) is the heater element.
And on the right side is the thermocouple connected with the pmmc.

Heater element

This instrument consists of the heater element for converting applied electrical energy into heat energy. One of the main reasons to use this instrument is that this instrument can be used to measure current and voltages at very high frequencies. And to be able to do this the heater elements must be free from skin effect.

So to minimize the skin effect in the heater element you must use high resistance thin wire made up from non-magnetic material.

Thermo element

Thermo element combines the heater elements with the thermocouple, and then it acts as an energy converter is known as the thermoelement.

Four types of thermoelements are listed below:

  • Contact type
  • Non-contact type
  • Vacuum type
  • Bridge type

Advantages of thermocouple

  • This instrument has very high sensitivity
  • These are not affected by stray magnetic fields
  • Thermocouple indicates the RMS value of the current or voltage irrespective of the waveform
  • The thermocouple is free from frequency error so it can be used for a wide range of frequency

Disadvantages of thermocouple

  • The overload capacity of this instrument is considerably low as compared to the other instrument.
  • Considerable power loss due to poor efficiency of thermal conversion

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