Thermocouple Experiment

SPARK-KING

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(Engineering Lectures and Engineering Solutions)

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09833066325 / 08796149007

2010

VIJAY BALU RASKAR

BE-Electrical / MBA - Operation

[Engineering Assignments]

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DESIGNED BY, PROF. VIJAY BALU RASKAR

SPARK-KING ….. Unique solution for Learning. VBR

Experiment No:

Title: Principle of thermocouple & characteristics of

different thermocouple

Roll No:

Batch:

Date:

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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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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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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 C900

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 C900

RTD PT 100 Sensor: Set point – strictly up to C500

OBSERVATION TABLE:

Sr.

No.

Furnace Temperature )( C J T/C output (mV) PT – 100 (Ohm)

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

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GRAPH:

Draw a Graph for FT VS J T/C Output and FT VS PT-100

CALCULATION:

TRC 385.0100

Where, CR 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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CIRCUIT DIAGRAM:-

Education

Thermocouple Experiment