In this section we will read about
- Current to pressure Converter (I/P Converter)
- Control Valve positioner or Pneumatic positioner
- Parts of a pneumatic control valve positioner
- Control Valve and its types
- Solenoid Valve
- Pneumatic Cylinder
- Butterfly Valve
- Globe Valve or pneumatic globe valve
- Parts of a Control Valve
- Pneumatic globe valve types
- Control Valve Characteristics
- Class of a control valve
- Pressure Transmitter
- pressure transmitter working principle
- Pin type pressure Transmitter
- Pressure Transmitter connections
- pressure transmitter signal checking
- Flow transmitter
In this lesson, we will study about Thermocouple.
- A thermocouple is also a temperature-sensing device.
- As the name Indicates Thermo means temperature and couple means a pair that means Thermocouple is used to measure Temperature and it has 2 wires.
- In thermocouples, only two wires are there.
- These two wires are short-circuited at one end.
- A thermocouple consists of two conductors of different materials (usually metal alloys) that produce a voltage in the vicinity of the point where the two conductors are in contact as shown in the above figure.
- the above line can be better understand by-
In thermocouples, two junctions are formed, one is hot junction in which the thermocouple is inserted and the other one is a cold junction -the part of thermocouple remains in environment.
Thermocouple Gives output as milli-volt.
So, we can say that thermocouple is a Temperature Sensor or temperature sensing device which gives output as milli volt.
- The voltage produced is dependent on, but not necessarily proportional to, the difference of temperature of the junction to other parts of those conductors.
- a thermocouple works for higher temperature ranges.
- A thermocouple works on the Seebeck effect.
- when two junctions of differenent temperatures are formed, then due to this temperature difference an emf is generated. This emf is produced in milli volts (mv).
- In, 1821 T. J. Seebeck observed the existence of an electromotive force (EMF) at the junction formed between two dissimilar metals (Seebeck effect).
- Seebeck effect is actually the combined result of two other phenomena, Thomson and Peltier effects.
- Thomson observed the existence of an EMF due to the contact of two dissimilar metals at the junction temperature.
- Peltier discovered that temperature gradients along conductors in a circuit generate an EMF.
How to check a Thermocouple
- In thermocouple millivolts (mv) are checked. As the temperature increases, millivolts are also increased. 1 millivolt is approximately equal to 25 Degree Celsius for Type K (Type K is the most common general-purpose thermocouple). A table is also used for calculating temperature.
- Two wires of thermocouple are short-circuited at one end. So we also check the continuity.
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