exp 6 thermocouple

7/27/2019 Exp 6 Thermocouple

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Chan Kah Fai 1001025381EE 102 Mechanics and Strength of Materials [Mr. Naveen]23 Feb 2011

ELEMENTS OF MATERIAL SCIENCE LAB REPORT

EXPERIMENT 6: THERMOCOUPLE CALIBRATION

CHAN KAH FAI (GROUP 4)

SCHOOL OF ENGINEERING

FACULTY OF ENGINEERING, ARCHITECTURE & BUILT

ENVIRONMENT

23 FEBRUARY 2011


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Table of Contents

Contents Page

Number

1.0 Introduction 3

2.0 Objectives 4

3.0 Material and Methodology 4

4.0 Procedure 5

5.0 Results 6

6.0 Discussions 6

7.0 Conclusions 8

8.0 Limitations of the Experiment/ Difficulties Encountered 8

9.0 Reference 8


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1.0 Introduction

When two different metals are connected with each other in a loop to form two

junctions, a small voltage potential or known as electromotive force (emf) will be

generated at two different temperatures where the current will be flow through the

loop circuit. To measure such small difference of emf in the circuit, a thermocouple

which plugged to a multimeter is used. Thermocouple is a type of temperature sensor

widely used to measure and control temperatures. It can be used to convert heat into

electric power as well. The advantages of using thermocouple as a temperature sensor

compare to other devices is they are inexpensive and interchangeable supplied with a

standard connectors and can measure up to a wide range of temperatures. The main

limitation of using a thermocouple is the accuracy to achieve precise temperature up

to 1 degree Centigrade, C.

By discovering the principle by a physicist, Thomas Johann Seebeck in 1821,

when any conductor is subjected to a thermal gradient, a voltage will be generated

known as thermoelectric effect. For typical metals used in thermocouples, the output

voltage increases almost linearly with the temperature difference over a bounded

range of temperatures which enable the device to measure a wide range of

temperatures. There are many types of thermocouples as well to measure certain types

of temperatures depending on the sensitivity of the measurements. Example types of

thermocouples are Type B, R, S, T, C, M, K, J, N where each types shows different

types of metals used for the circuit.

Thermocouple is one of the most suitable sensors used in industrial processes

such as steel industries, diesel industries, oil industries and etc to measure over a large

temperature range, up to 2300C. However, it is not suitable to be used for smaller

temperature differences, with 0.1C due to its limitations.


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2.0 Objectives

1. To identify the ways to operate and calibrate a thermocouple.

2. To identify the corresponding curve-fit correlation.

3.0 Material and Methodology

Materials : Distilled water

Apparatus : Thermocouple, 500.0 ml beaker, thermometer, multimeter, magnetic

stirrer with hot plate, retort stand.


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Figure 6: Thermocouple Calibration

4.0 Procedure

1. The apparatus is assembled as shown in the diagram above.

2. 350.0 ml of water is poured into a 500.0 ml beaker.

3. The hot plate is turned on to increased the temperature of the water in the

beaker.

4. The water in the beaker is heated to the desired temperature (30 C initially).

The hot plate is switched off once the temperature is found.

5. The ends of the thermocouple are connected to the digital multimeter (MM)

and the multimeter is set to read in millivolts DC.

6. One junction of the thermocouple is dipped in the thermo-bath liquid and wait

for few minutes to allow the reading to reach a steady state except for the last

digit.

7. The sensor wire is hold carefully to prevent the contact to the circulators

propeller.

8. The initial digital MM reading is noted in millivolts (EMM) and steps 4 to steps

7 are repeated by increasing 5 C from 30C to 60C.

9. As mentioned in the theory, the multimeter reading corresponds to the

difference in temperature between surroundings and the bath. In order to

calibrate the thermocouple, the room temperature is taken into consideration to

get the absolute value of temperature measured. The equivalent millivolt value

for the room temperature is found from the corresponding thermocouple table

(ERM). By using that millivolt value, corresponding to the room temperature,

adds to every multimeter reading (EMM). The values are tabulated.


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5.0 Results

Temperature

(C)25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0

Readings/

EMM, (mV)0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

6.0 Discussions

1. Plot the measured bath temperatures values (TB) on x-axis against the

corresponding thermocouple emf (millivolt) values (E) on y-axis.

Graph of Readings (EMM) against Temperature

R2

= 1

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

25 .0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0

Temperature/C

ReadingsEMM/mV

Diagram 6.1: Graph of Readings (EMM) against Temperature

2. Find the slope, intercept and the correlation coefficient of the curve-fitted line

by any method. If the correlation is not very close to one, curve fit higher

order polynomial.

Slope: y2 y1 = m(x2 x1)

Using temperature at 30C and 35C,

0.04 0.02 = m(35.0 30.0)

0.02 = m(5.0)

Therefore, slope, m = 0.004


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Intercept: y = mx + c

Using temperature at 30C,

0.02 = 0.004(30.0) + c

c = -0.1

Therefore, intercept at y-axis = -0.1

intercept at x-axis = 25.0

From the graph drawn above, we know that the R2

= 1.

Therefore, the correlation coefficient of the curve-fitted line is 1 which is the

best line fitted graph.

With the data recorded, using a thermocouple, we are able to measure the

temperatures of the water in the beaker. By connecting two different metals to the

multimeter and immerse one junction into the heating water, the thermocouple would

measure the small difference of the voltage generated where the current completes

through the loop circuit.

A graph is plotted based on the data collected, it is shown that by increasing

5C for each temperatures from 25C to 60C, the output for the voltage increases by

0.02 millivolts respectively. Tabulating the results recorded, a linear graph is plotted.

By understanding that the output voltage increases almost linearly with the

temperature differences over a range of temperatures as shown in the graph above,

this enable the thermocouple to measure a wide range of temperatures. However,

different types of metals need to taken into consideration to measure different range

of temperatures.


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7.0 Conclusions

As for the conclusion of the experiment, we are able to measure the

temperatures of the water in the beaker by calibrating a thermocouple. Upon

completing the experiment, with the data recorded, a graph could be plotted which is

the output voltage against temperature.

Analyzing the graph plotted, we are able to find out the graph is a linear type

graph. This shows that the voltage increases linearly with the temperature differences

over a range of temperatures taken. Therefore, thermocouple is a suitable device to

used measure a wide range of temperatures in industrial processes without spending

on other expensive measuring devices and risking lives especially in heavy industries.

8.0 Limitations of the Experiment/ Difficulties Encountered:

1. We are unable to know which type of thermocouple to be use to measure the

temperature of the water in the beaker due to unfamiliar with many types of

thermocouples available.

2. When heater is turned on, we still need to depend on a thermometer to

measure the temperature of the water precisely instead of obtaining from

thermocouple.

3. The accuracy of a thermocouple is low, usually not better than 0.5 C, which

might not high enough for some other applications.

4. Thermocouples measure their own temperature. Therefore, we need to infer

the temperature of the object that there is no heat flow between them when

measurement is taken.

Reference

1. Incropera, F. P. and D. P. DeWitt, Fundamentals of Heat and Mass Transfer,

4th

edition, John Wiley and Sons Inc., New York, 1996.

2. No ownership (06 Jun 2003), Retrieved on 05 February 2011. From

http://www.temperatures.com/tcs.html

3. No ownership (06 Jun 2003), Retrieved on 05 February 2011. From

http://www.efunda.com/designstandards/sensors/thermocouples/thmcpleintro.

cfm

exp 6 thermocouple

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