THERMOCOUPLE
What is Thermocouple?
- Thermocouple is an electrical device which use to measure temperature.
- Thermocouple can be defined as a kind of temperature sensor that is used to measure the temperature
- The two different metal wires were connected at one end of the junction in the circuit when temperature applied to the junction, the current will be generated in the circuit which is known as an electromagnetic field.
- the energy will generate in the circuit is called a Seebeck effect.
- This EMF calculated In mV in terms of temperature. the common devices used to measure EMF are voltage balancing potentiometer and the ordinary galvanometer.
Working principle of thermocouple
- The main working principle of the thermocouple is the Seebeck effect, Peltier and Thompson.
- Seebeck effect: this type of effect occurs among two dissimilar metals. When the heat applied to one of the metal wire, the flow of electrons passes through a hot metal wire to a cold metal wire in the circuit.
- Peltier effect: this Peltier effect is opposite to the Seebeck effect. When the voltage source applied to the two dissimilar metal wires, the temperature ( hot and cold) generate at junctions.
- Thompson effect: Thomson suggested that when a
current flows through unequally heated conductors, heat energy is absorbed or
evolved throughout the body of the metal.
Construction of thermocouple
- Thermocouple consist of two dissimilar metal wire that
are connected together at the junction end.
- This junction named as measuring end. there are three
types of junction named as Undergrounded junction, grounded junction, exposed
junction.
- Undergrounded junction:
In this type of junction, the conductors are totally separated from the
protecting cover.
- The applications of this junction mainly include
high-pressure application works.
- The main benefit of using this function is to
decrease the stray magnetic field effect.
- Grounded junction: In
this type of junction, the metal wires as well as protecting cover are
connected together. This function is used to measure the temperature in the
acidic atmosphere, and it supplies resistance to the noise.
- Exposed junction: The
exposed junction is applicable in the areas where a quick response is required.
This type of junction is used to measure the gas temperature. The metal used to
make the thermocouple basically depends on the calculating range of
temperature.
- Thermocouple is
designed with two different metal wires that make in detecting element by
connecting at one junction that is named as a hot junction and second named as
cold junction. Among these two junctions, one junction is connected by a voltmeter
or transmitter where the cold junction and second junction is associated in
a process that is called as a hot junction.
Advantages & Disadvantages of Thermocouple
The advantages include
the following.
- Accuracy is high
- It is Robust and can be used in environments like harsh as well as high vibration.
- The thermal reaction is fast
- The operating range of the temperature is wide.
- Wide operating temperature range
- Cost is low and extremely consistent
The disadvantages
include the following.
- Nonlinearity
- Least stability
- Low voltage
- Reference is required
- Least sensitivity
- The thermocouple recalibration is hard
Thermocouple Applications
- These are used as the temperature sensors in thermostats in offices, homes, offices & businesses.
- These are used in industries for monitoring temperatures of metals in iron, aluminum, and metal.
- These are used in the food industry for cryogenic and Low-temperature applications. Thermocouples are used as a heat pump for performing thermoelectric cooling.
- These are used to test temperature in the chemical plants, petroleum plants.
- These are used in gas machines for detecting the pilot flame.
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