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