Electrical Engineering Experiment

1. 2010
SPARK-KING
Knowledge is NO-WHERE …..
(Engineering Lectures and Engineering Solutions)
vijayraskar2003@yahoo.co.in
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VIJAY BALU RASKAR
BE-Electrical / MBA - Operation
[Engineering Assignments]

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Experiment No:
Title: Principle of thermocouple & characteristics of
different thermocouple
Roll No:
Batch:
Date:
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DESIGNED BY, PROF. VIJAY BALU RASKAR

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EXPERIMENT NO.
PRINCIPLE THERMOCOUPLE AND CHARACTERISTICS OF
DIFFERENT THERMOCOUPLE
TITLE: To understand the principle of thermocouple & to obtain characteristics of
different thermocouples.
AIM: To plot characteristics of thermocouple and find out non linearity.
APPARATUS: Heater, Multimeter, Thermocouple, Water OR Thermocouple Trainer
THEORY:
A thermocouple consists of a pair of dissimilar metal wires joined together at one end,
terminating at the other end, which is maintained at known temperature. In industrial
application choice of material used to make up thermocouple depends on the
temperature. Temperature should be measured using devices that measure
temperature. It is based on see back effect that when two different metals having work
junction when placed together, a voltage is generated at the junction. This principle is
used to convert heat energy into electrical energy. Thermocouple type instrument can
be used for both A.C. and D.C. application. Most attractive feature is that they are used
for measurement of voltage current at high frequency. In fact these instruments are very
accurate when above 50 Hz.
CONSTRUCTION: Thermocouple consists of two dissimilar wires as to form two
junctions. One junction is kept at constant and other is heated. Hot junction is called as
measuring junction and cold junction is called as reference junction. Thermocouple may
be prepared by casting two wires together. Thermocouple conductor must be insulated
from hot junction to the indicating instrument. The two wires should not touch each
other. Therefore suitable insulating material must be used accordingly.
Temperature ranges for insulating:
1. Enameled and cotton : 250 0 F
2. Glass and asbestos : 900 0 F
3. Ceramic : 2600 0 F
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DESIGNED BY, PROF. VIJAY BALU RASKAR

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On the basis of the thermoelectric principle of the thermocouple, the material decided
into and base type material.
Thermocouple doesn’t use rare conductors except in application where atmospheric
condition permits the leads and junctions are internally insulated from sheet using
various plotting component. They are normally installed in particular walls so that they
may easily be removed or replaced without interaction and shut down plan.
PRINCIPLE: Device that measured temperature on the basis of thermoelectric principle
is called as thermocouple. The thermocouple principle given below on emf generated
across the junction of dissimilar metal when junction is heated.
1. See back effect: If close circuit are formed by two dissimilar metals at different
temperatures then current flow from hot junction produces a proportional voltage
at the junction.
2. Peltier effect: When loop was formed by two dissimilar metals and if externally
current was forced to flow through one junction of bridge is heated cold junction.
3. Thomson’s effect: When current flowing through copper wire whose temperature
vary from point heat when current at any direction is in same direction of current
flow. While heat is absorbed at point if current in opposite direction of heat flow..
WORKING: Since, thermocouple emf depends upon the difference in temperature eat
junction the temperature of water should remain absolutely constant in order to calibrate
thermocouple to reduce errors due to change in ambient temperature. Reference
temperature should be kept at 00 C and thermocouple can be used up to 14000 C.
ADVANTAGES:
1. Cheaper than RTD.
2. Good reproducibility
3. Speed of response is high
4. Accuracy is high
5. Rugged construction
DISADVANTAGES:
1. Cold junction and lead compensation is required
2. Needs signal amplification
3. Exhibits non linearity
PROCEDURE:
 Ensure the following points –
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DESIGNED BY, PROF. VIJAY BALU RASKAR

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o Main supply is single phase.
o Furnace is off and sensor is in place.
o Fan is off and away from furnace.
o Sensor under calibration is removed from furnace.
o The set point at temperature controller is set below 900C
1. Put water inside the tank in appropriate level.
2. Insert sensor in the furnace (K-Type or PT-100)
3. Connect multimeter at PT-100 (ohm)
4. Connect multimeter at K-type (mV)
5. Connect trainer to main power supply.
6. Noted down all the readings in different interval of time.
NOTE:-
 J/K Thermocouple Sensor:- Set point – strictly up to 900C
 RTD PT 100 Sensor: Set point – strictly up to 500C
OBSERVATION TABLE:
Sr. Furnace Temperature (C ) J T/C output (mV) PT – 100 (Ohm)
No.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
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DESIGNED BY, PROF. VIJAY BALU RASKAR

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GRAPH:
Draw a Graph for FT VS J T/C Output and FT VS PT-100
CALCULATION:
RC  100  0.385T
Where, RC  Resistance at temperature T (C )
T = Temerature at 100 (C )
The increase in resistance is linear, the relationship between resistance changesand
temperature rise being 0.385 Ω /°C
RESULT:-
We calculated the resistance at Temperature and also find the thermocouple output by
using multimeter. For, _______ (C ) we get _____ mV and ______ohm
CONCLUSION:
Thus, we have studied construction and working of thermocouple and determined its
sensitivity and linearity.
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DESIGNED BY, PROF. VIJAY BALU RASKAR

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CIRCUIT DIAGRAM:-
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DESIGNED BY, PROF. VIJAY BALU RASKAR