DEVELOPMENT OF AN APPARATUS FOR
MEASURING SEEBECK COEFFICIENT AT HIGH
TEMPERATURES
AZKA NASEER
KIA KHUR FAISAL
MAZAHIR ABBAS
AMNA IDREES
(160735)
(160751)
(160069)
(160743)
BS PHYSICS (FALL 2016-2020)
Project Supervisor
Dr.Rizwan Akram
Assistant Professor
DEPARTMENT OF PHYSICS
AIR UNIVERSITY, ISLAMABAD
DEVELOPMENT OF AN APPARATUS FOR
MEASURING SEEBECK COEFFICIENT AT HIGH
TEMPERATURES
Final Year Project Report
(FALL 2016-2020)
DEPARTMENT OF PHYSICS
i
DEVELOPMENT OF
APPARATUS FOR
MEASURING
SEEBECK
COEFFICIENT AT
HIGH
TEMPERATURES
Submitted by:
AZKA NASEER
(160735)
KIA KHUR FAISAL (160751)
MAZAHIR ABBAS
(160069)
AMNA IDREES
(160743)
Project Supervisor
---------------------------------------------
ii
Dr. Rizwan Akram
Assistant Professor
Head of Department
--------------------------------------------Dr Mozaffar Husain
Chair Department
ACKNOWLEDGEMENT
“In the Name of Allah, the Most Beneficent, the Most Merciful All
the praises and thanks be to Allah. The Most Beneficent, the Most
Merciful”
We won’t able to complete our work without the indiscernible help of
ALMIGHTY ALLAH Also we can’t thank enough to our supervisor DR.
RIZWAN AKRAM for his motivation, enthusiasm the methodology to carry
out the research and to present the research works as clearly as possible. It was
a great privilege and honor to work and study under his guidance. We are
extremely grateful for what he has offered us. We would also like to thank him
for his friendship, empathy, and great sense of humor. We wish to convey our
gratitude to the respected institute Air University for giving us this opportunity
of learning and the Department of Physics.
iii
We would like to especially thank Dr Asghari Maqsood Dean of faculty of
Basic and Applied sciences, Dr Mozaffar Hussain Head of Department of
Physics who motivated and guided us through each phase of this project. We
would like to thank our colleagues and friends for discussions, suggestions and
criticism. Many people have participated in the experiments for this research
and especially to our seniors who helped us in making the device.
We are extremely grateful to my parents for their love, prayers, caring and
sacrifices for educating and preparing me for my future. Also we express my
thanks to our siblings for understanding and continuing support to complete this
research work
Finally, we would like to thank every member of the faculty for being an
invaluable guidance. Surely, without them, this project would not have been
possible for us.
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v
ABSTRACT
The Seebeck Effect was discovered by the Baltic German physicist Thomas
Johann Seebeck. The Seebeck Effect is a phenomenon in which a temperature
difference between two dissimilar electric conductors or semiconductors
produces a voltage difference between those two substances. When heat is
applied to one of the two conductors or semiconductors, the electrons become
excited due to the heat. Since only one of the two sides is heated, the electrons
start moving towards the cooler side of the two conductors. If both of the
conductors are connected in the form of a circuit, a direct current flows through
the circuit.
It has wide variety of applications (Thermocouples, Actuate electronic switches,
Thermoelectric cooling, Thermometers, Power generation). Hence, its
measurement is crucial especially at high temperatures for both research and
commercial oriented purposes. Commercially available devices for measuring
the Seebeck coefficient are mostly for ambient temprature and easily accessible
for researchers and aspiring scientists, hence this project was commissioned to
provide a device for measuring the Seebeck coefficient at high temperature
using furnace.
This project titled, “DEVELOPMENT OF AN APPARATUS FOR
MEASURING
SEEBECK
COEFFICIENT
AT
HIGH
TEMPERATURES” incorporates every aspect of the Seebeck effect to design,
construct and deliver desired device and results.
This thesis puts in writing the complete process and the phases of the project
went through. Starting with a comprehensive literature survey of Seebeck effect
and thermoelectric effects, Objective of the project, ideal conditions limitations,
comparison of various designed geometries, properties of each component and
the final constructed device followed by results and conclusive remarks.
vi
LIST OF FIGURES
Figure 1. 1: Peltier device depicting a hot and cold side.................................. 3
Figure 1. 2: Thermocouple junction of two dissimilar metals. ......................... 4
Figure 1. 3: Ideal Seebeck coefficient measurement geometry. ....................... 7
Figure 2. 1: Two metal blocks and bar shape sample and K-TC .................... 10
Figure 2. 2: Two metal blocks and bar shape sample. ................................... 11
Figure 2. 3: Uni-axil four-point probe geometry, Two cylindrical metal blocks
and disk shape. ............................................................................................. 12
Figure 2. 4: Proposed design, Uni-axil four-point probe geometry, two Peltier's
implanted on two copper blocks and sandwiching the sample. ...................... 14
Figure 3. 1: Block diagram of apparatus. ...................................................... 17
Figure 3. 2: Sample Holder .......................................................................... 18
Figure 3. 3: Peltier Generator ....................................................................... 19
Figure 3. 4: Heat sink unit ............................................................................ 19
Figure 3. 5: Furnace body............................................................................. 21
Figure 3. 6: Coils ......................................................................................... 21
Figure 3. 7: Power Supply Unit 1 ................................................................. 22
Figure 3. 8: Power Supply Unit 2 ................................................................. 22
Figure 3. 9: Multimeter ................................................................................ 23
Figure 3. 10: K-Type Thermocouple ............................................................ 23
Figure 3. 11: Arduino UNO.......................................................................... 24
Figure 3. 12: MAX6675 ............................................................................... 25
Figure 3. 13: Screen ..................................................................................... 25
Figure 3. 14: Relays ..................................................................................... 26
Figure 3. 15: Potentiometer .......................................................................... 26
vii
Table of Contents
CHAPTER 1 .................................................................................................. 1
INTRODUCTION ......................................................................................... 1
1.1 THERMOELECTRIC EFFECT ............................................................ 2
1.2 TYPES OF THERMOELECTRIC EFFECT ......................................... 2
1.2.1 Peltier effect ................................................................................... 2
1.2.2 Seebeck effect: ............................................................................... 3
1.3 IMPORTANCE OF MEASUREMENT OF SEEBECK
COEFFICIENT .......................................................................................... 5
1.4 OBJECTIVE......................................................................................... 5
1.5 MEASUREMENT OF SEEBECKCOEFFICIENT ............................... 6
1.5.1 Ideal geometry ............................................................................... 6
1.5.2 Ideal conditions .............................................................................. 7
CHAPTER 2 .................................................................................................. 9
GEOMETRICAL ANALYSIS ....................................................................... 9
2.1 COMPARISON OF GEOMETRIES ................................................... 10
2.1.1 Geometry No 1: ............................................................................ 10
2.1.2 Geometry No 2: ............................................................................ 11
2.1.3 Geometry No 3:............................................................................ 12
2.1.4 Proposed Geometry: ..................................................................... 13
CHAPTER 3 ................................................................................................ 16
CONSTRUCTION OF DEVICE .................................................................. 16
3.1 OVERVIEW....................................................................................... 17
3.2 DETAILS OF DEVICE ...................................................................... 17
3.2.1 Sample Holder: ............................................................................ 18
3.2.2 Peltier Generator: ......................................................................... 18
3.2.3 Heat Sink Unit .............................................................................. 19
3.3 DETAILS OF DEVICE COMPONENTS ........................................... 20
3.3.1 Metal Body: ................................................................................. 20
3.3.2 Coils: ........................................................................................... 20
3.3.3 Thermal Insulation: ...................................................................... 21
viii
3.3.4 Power Supply: .............................................................................. 21
3.3.5 Digital Multimeter: ....................................................................... 23
3.3.6 Type-K Thermocouple: ................................................................ 23
3.3.7 Arduino UNO: ............................................................................. 24
3.3.8 MAX6675: ................................................................................... 24
3.3.9 Screen: ......................................................................................... 25
3.3.10 Relay: ......................................................................................... 26
3.3.11 Potentiometer: ............................................................................ 26
CHAPTER 4 ................................................................................................ 27
WORKING AND DISCUSSION ................................................................. 27
4.1 PREVIEW: ......................................................................................... 28
4.2 WORKING: ....................................................................................... 28
4.2.1 Temperature Difference:............................................................... 28
4.2.2 High Temperatures: ...................................................................... 28
4.2.3 ELECTRONICS:.......................................................................... 28
4.2.4 Code: ........................................................................................... 29
4.3 MEASUREMENT METHODOLOGY ............................................... 42
4.4 RESULTS AND DISCUSSION.......................................................... 42
4.5 CONCLUSION .................................................................................. 42
ix
CHAPTER 1
INTRODUCTION
1
1.1 THERMOELECTRIC EFFECT
Direct transformation of temperature difference to voltage or we can say
transformation of heat to electrical energy is called thermoelectric effect.
One of the applications of thermoelectric effect is production of electricity.
We can find variation in temperature of the object or the values of the
temperature. We can also the use thermoelectric devices to control temperature.
Thermoelectric devices create electric current and causes difference of
temperature in each side of the metal and if we provide voltage the heat will
flow from one side to the other side.
When observing the situation on atomic level when there is difference of
temperature between two sides of dissimilar metals in that case charge carriers
will move from hot side to cold side which develops potential difference so we
can say that applied voltage determines the direction of heat flow.
1.2 TYPES OF THERMOELECTRIC EFFECT
Main types of thermoelectric effect are:
● Peltier effect
● Seebeck
1.2.1 Peltier effect
2
The difference of temperature which is created by applying voltage between
two electrodes which are connected to a sample of semiconductor.
On smaller scales it is used for transferring heat from one medium to another.
This phenomenon is known as Peltier effect which can be seen from figure 1.1.
Figure 1. 1: Peltier device depicting a hot and cold side.
1.2.2 Seebeck effect:
At unlike temperature values when two dissimilar electrical conductors or
semiconductors generate potential difference then this phenomenon is known
as Seebeck effect.
When we apply heat in the above case to one side and the other side is not heated
then the electrons flow from hotter end to the cold end.
3
∆V ∝ ∆T
∆V = S∆T
S = ∆V/∆T
Figure 1. 2: Thermocouple junction of two dissimilar metals.
Here ‘S’ represents Seebeck coefficient, ‘V’ represents the potential difference
and ‘T’ represents temperature.
Seebeck coefficient is one of the intrinsic properties of materials. It varies with
the impurities present in the materials.
Basically this effect is responsible for how thermocouples behave, which in turn
are used to approximate observed temperature differences or in electronic
switches to turn large systems on and off.
4
1.3 IMPORTANCE OF MEASUREMENT OF
SEEBECK COEFFICIENT
While dealing with thermoelectric devices checking that how much efficient
they are and is very important that’s why we measure Seebeck coefficient. We
also need to find figure of merit and conversion of heat to electricity of materials
which shows thermoelectricity as it is an integral part of thermoelectric
materials. So for the calculation of Seebeck coefficient the relation is written as
𝑍𝑇 = 𝑆^2𝛼𝑇/K
Here ZT represents figure of merit, K is thermal conductance of material, S
represents Seebeck coefficient, α is thermal conductivity, T is temperature of
figure of merit.
In this modern era we need some green energy sources which can be done
through thermoelectric generators and we can get efficiency of those
thermoelectric generators through figure of merit which includes figure of
merit.
Seebeck coefficient gives us information such as impurities in the sample and
its measurement at room temperature is of great importance to us or testing it in
research field or laboratory.
In remote areas thermoelectric generators are used as power supply. One
interesting fact about thermoelectric devices is the use of the heat wasted in
many devices while using them to get energy and if we measure Seebeck
coefficient we can convert that heat being wasted into useful energy or we can
say in renewable energy source.
1.4 OBJECTIVE
Our objective is to simply develop a device fabricated in lab which can
measure Seebeck coefficient at high temperatures.
5
1.5 MEASUREMENT OF SEEBECKCOEFFICIENT
There are many questions that which measurement technique provides us with
the most accurate results to determine Seebeck coefficient at high temperatures.
For determining the technique which gives the most accurate results we
implement ideal and nonideal practices to see that which materials have high
ZT.
For measuring Seebeck coefficient reliably, temperature and potential must be
taken at the same point inside the sample. The probes which we attach to the
sample cause the temperature to jump between the probes and the sample.
Generally, the Seebeck coefficient depends on temperature so the potential
difference we measure varies nonlinearly with temperature difference. [1]
When our sample to be tested for measuring Seebeck coefficient is easy, we just
need to know the temperature of the two faces and potential difference
developed between those two faces or sides but, for ideal conditions we need to
look into a lot different factors which can affect the measurement of Seebeck
coefficient.
1.5.1 Ideal geometry
Ideal geometry for measuring Seebeck coefficient is shown in figure 1.3 In the
above figure probe is connected to the sample directly.
Probes act as thermocouples and voltage leads both which measure the
temperature and potential difference.
6
Figure 1. 3: Ideal Seebeck coefficient measurement geometry.
1.5.2 Ideal conditions
● Simultaneous measurement of both temperature and potential
difference.
● Potential difference varies linearly with temperature.
● Values of both temperature and potential difference are measured at the
same point of the sample.
Contrary to the above ideal conditions we have these general or nonideal
conditions which arise because they are out of our capacity to achieve ideal
conditions.
● Measurement of temperature difference and potential difference occur
at different times. [2]
● Linear response is not possible practically because sometimes nonzero
potential difference for high temperature ranges from few microvolts to
one millivolt that causes offset in voltage measurement or because at ∆T
= 0 we have not sufficient signals. [2]
7
● Measuring values of both potential difference and temperature at same
point is not possible because there is always some distance between the
two measurement sources which have to be measure both potential
difference and temperature.
…………………………………………….
8
CHAPTER 2
GEOMETRICAL
ANALYSIS
9
2.1 COMPARISON OF GEOMETRIES
In this segment, different geometries of the device to be built are planned and
analyzed. Each plan offers a one of a kind quality which is assessed dependent
on generally applicable to perfect geometry as examined.
2.1.1 Geometry No 1:
The following are the leading geometries:
Figure 2. 1: Two metal blocks and bar shape sample and K-TC
Figure 2.1 shows that two metal squares are sandwiching the example in the
middle of as a bar and embedded in the metal squares are two thermocouples
which are not associated legitimately to the example.
Here and there the substance response happens between the example and the
thermocouple so this has the preferences that it stays away from the response
between the example and thermocouple which happens because of direct
contact of the thermocouple to the framework, however there are a ton of other
inherent issues with this framework that there is contact opposition present in
10
the metal squares as far as warm and electrical, and just as between the essences
of the square and the example. These issues at that point lead to balance in the
temperature just as in voltage estimation.
2.1.2 Geometry No 2:
Figure 2. 2: Two metal blocks and bar shape sample.
Figure 2.2 shows that an example in type of a long bar is sandwiched in the
middle of 2 metal square that goes about as a source and sink for warmth and
two tests that are legitimately in contact with the example for the estimation of
voltage and temperature distinction. This structure has the favorable position
over the first appeared in figure 1 that it sidesteps the contact obstruction
between the example and metal square yet there is a great deal of different issues
that despite everything exist, that is the immediate association of the test of the
thermocouple to the example may remove heat from the example and can cause
temperature contrast over the wire of the thermocouple which will influence the
consequence of temperature and voltage estimation. Furthermore, the
thermocouple is reaching recently so it likewise makes high contact obstruction
11
on the grounds that for not having great contact with the example, to guarantee
it to reach test it needs some power, which can harm the example as a large
portion of the thermoelectrical material is fragile. Since the thermocouple is
connected recently to a position which doesn't have a huge estimation of
temperature distinction which don't shows apparent outcome in voltage
estimation and this plan just acknowledges bar-molded example which may
then be harmed because of weakness of thermoelectrical material so enormous
shape geometry isn't reasonable for the estimation.
2.1.3 Geometry No 3:
Figure 2. 3: Uni-axil four-point probe geometry, Two cylindrical metal blocks and disk
shape.
Figure 2.3 shows the geometry which has numerous points of interest over
different geometries. This has the four-point test which lessens the contact
opposition. Such a uniaxial planned 4-point Seebeck framework thought has
12
been taken from the NASA-JPL in 1890, which has a crucial build up an
instrument which has a light funnel to flexibly a dynamic ∆𝑇 [6]. A round and
hollow square which goes about as a radiator produced using boron nitride,
having an opening completely which is utilized to pass a thermocouple test
autonomously, having a little breadth when contrasted with the gap in it, that
associates thermocouple straightforwardly to the example.
The upsides of the framework are:
● Thermocouple is straightforwardly associated with the example
● Since thermocouple is vertically embedded through the opening, which
is available in the focal point of round and hollow squares, it permits
thermocouple to apply enormous enough power on the example to
diminish contact obstruction.
● Thermocouple is associated with a locale, made by cozy contact of test
surface and warmer where the temperature is practically steady.
Despite the fact that this is the best plan, yet it has some geometry limitations
that is, it just acknowledges a plate formed article, it utilizes a curl to warm the
example which may harm the example, this structure is made distinctly for
higher temperature.
2.1.4 Proposed Geometry:
The arrangement is gathered in a rectangular manufacture. Two Peltier
determined up to 51.4 watts of warmth dispersal. Pinnacle or greatest force
contribution of 15.4V DC, 6A are set inside the manufacture confronting each
other having enough space between them to take into account the two copper
squares (Cu) and the example that are to be put in the middle of this space.
Between these two Peltier, two copper squares are mounted on those sides of
the Peltier which are confronting one another. The utilization of copper squares
instead of some other conduit/metal is legitimized by its high warm conductivity
(386 Wm-1K-1) at room temperature. The example is set in between these two
upsides down copper squares while being in contact with both copper squares.
The sides of the example are secured with a protector to deny any outside
temperature influencing the example.
13
The figure shows the schematics of the Seebeck coefficient measurement
apparatus proposed design.
Figure 2. 4: Proposed design, Uni-axil four-point probe geometry, two Peltier's implanted on two
copper blocks and sandwiching the sample.
.
The temperature of each square is identified with that side of the example which
is in contact. The separation between copper squares is flexible to let different
examples fit in. For the estimation of temperature, two thermocouples are
utilized.
Thermocouple-1 is penetrated from the upper side of the upper Peltier going
through the upper copper square which don't contact the copper squares and
secured by protecting material square and simply reaching the example on the
upper side. Thermocouple-2 is bored from the lower side of the lower Peltier
going through the lower copper square and simply reaching the example on the
lower side. This structure has numerous points of interest over the other, it
acknowledges numerous geometrical states of an example like plates, square
and square shape.
14
Thermocouple is legitimately associated with the example vertically through the
gap, which applies a power on the example and make a tight association with
the example which decreases the contact opposition. Microvoltmeter will be
utilized for the estimation of possible contrast. Since this the four-point test
framework which is utilized to lessen contact protections and other vulnerability
in estimations.
To quantify temperature with thermocouples gives a bit of leeway that in
outrageous conditions were generally utilized thermometers are not, at this point
utilitarian, the thermocouples despite everything do work. Different points of
interest that thermocouple give are that they are less exorbitant, dependable and
fitting to work over wide temperature ranges.
…………………………………………….
15
CHAPTER 3
CONSTRUCTION OF
DEVICE
16
3.1 OVERVIEW
Device was already present for measuring Seebeck co-efficient at room
temperatures which have following components
Figure 3. 1: Block diagram of apparatus.
Here the block diagram of apparatus for measuring Seebeck coefficient at room
temperature consisting of copper block which are attached to Peltier. Each
peltier has heat sink for removing excess heat. Thermocouples are attached for
measuring the temperature also multimeter is attached to them. Two power
supplies are given which will be discussed later in this chapter. Further for
measuring See beck at high temperature a device has been constructed with coils
and inside a metal body. Each of its components and construction are given in
this chapter
3.2 DETAILS OF DEVICE
Previously available apparatus has following components listed and explained
below;
17
3.2.1 Sample Holder:
A sample holder was used where material that has to be tested is placed. It is
rectangular bar of copper transformed to cylindrical shape having diameter of
16mm and 20mm height. Similarly, a seat of 2mm and 13mm diameter is made in
this cylindrical bar using lath machine. A thermocouple is used to connect a MAX6675
by drilling hole in a sample. Copper has thermal conductivity of 386 W/mK.
Figure 3. 2: Sample Holder
3.2.2 Peltier Generator:
Peltier has rectangular shape and it is attached to sample holder on both sides to
create a temperature difference for the material that is placed in it. For attaching
Peltier thermal paste is used and heat can be using travel through that. Power
consumption is about 70 watt with each Peltier is of 12V and 6A. This size of
Peltier is used because it gives minimum error as the sample is small one side
is getting hot and other cold otherwise whole material will get hot and will not
give desire result.
18
Figure 3. 3: Peltier Generator
3.2.3 Heat Sink Unit
A heat sink is attached to the device to take extra heat away. It consists of heat
sink and fan. It is a precautionary measure while doing the experiment since the
size of sample is small. It is important to give away extra heat.
Figure 3. 4: Heat sink unit
19
3.3 DETAILS OF DEVICE COMPONENTS
3.3.1 Metal Body:
For measuring See beck at high temperature metal body is constructed having
height 2.1 inches and length of 6 inches (3 inches inner). Rectangular shape is
given because sample can be easily heated as the area where sample is placed
i.e. sample holder it is small. One side is left intentionally made as gate for
convenience. Hooks have been added for attaching coils. It has been left hollow
from inside for thermal insulation.
Figure 3.5: Coils
3.3.2 Coils:
Coils having temperature range of 400°C have been used because they are easily
available. These coils are made from Nichrome wire. The coils are connected
to a 2-Channel relay board which is controlled by Arduino. These coils are
attached on the hooks of square shape metal body so it can be easily changed in
case any of coil gets damaged. Three coils are used for getting the desired
temperature and range of 310°C was easily achieved using these coils so far.
20
Figure 3. 6: Coils
3.3.3 Thermal Insulation:
For thermal insulation of metal body plaster of Paris (1200°C) is filled inside
the furnace. Also a ceramic fiber HPS (2300⁰F/1260⁰C) is used as an extra layer
for thermal insulation. HPS Blanket is made from a blend of Alumina and Silica.
Both of these are used to avoid heat loss.
3.3.4 Power Supply:
To operate device, it is needed to some source power, here it is provided with
two different power supply.
Power supply 1:
This is a variable power supply which changes voltage from 0 volt to 30 volts,
and 10 amperes current, this power supply is connected to only one Peltier
generator which has to produce a heating effect. This is used because of to have
controlled on voltage so that the Peltier is preventing from burning and have
desire value of voltage which turn create temperature difference.
21
Figure 3. 7: Power Supply Unit 1
Power supply 2:
This variable power supply has a specific value of the voltage that is ±3V, ±5V,
±12V which is then connected to one Peltier generator which has to produce a
cooling effect and also it is connected to heat sink unit.
Figure 3. 8: Power Supply Unit 2
22
3.3.5 Digital Multimeter:
A multimeter is used to read quantity in digital value. It is connected to sample
show the thermoelectric voltage produces in the experiment.
Figure 3. 9: Multimeter
3.3.6 Type-K Thermocouple:
Most widely used thermocouple having range of 0-1024°C. It has wider range
and accuracy of +/- 2.2C or +/- .75%. Two thermocouples are directly attached
to sample holder by drilling for measuring most accurate temperature and the
third one is attached to furnace. One of the main reason of using this type of
thermocouple is that they are easily available in case any of them gets damaged.
Figure 3.10: K-Type Thermocouple
23
3.3.7 Arduino UNO:
Arduino Uno is a microcontroller board baes on ATmega328P. It has 14 digital
input/output pins consisting of 6 output pins for PWM signal, 6 pins for
analogue, a 16 MHz ceramic resonator, ICSP header and a push button. It
connects to computer via USB-B to USB-A type cable. It can be powered via
2.1mm DC adapter (7V-12V).
Figure 3.11: Arduino UNO
3.3.8 MAX6675:
Max6675 is an analogue to 12-bit digital signal converter and amplifier board.
It connects to Arduino board via SPI-interface (SCK, SO, CS). K-Type
thermocouples are used with it. It has capability of outputting 12-bit signal with
resolution of 0.25C. It can measure up to 1024C with accuracy of 8LSBs for up
to 700C.
24
Figure 3. 12:MAX6675
3.3.9 Screen:
Figure 3.13: Screen
We have used ST7789 single chip TFT IPS (1.3”) display having resolution of
240x240. It connects to Arduino via SPI interface (SDA, SCL, RES, DC). The
TFT screen is capable of refreshing data at 60Hz with delay of 1ms. It also has
an in-built voltage regulator to protect from over input voltages. The display is
used to show the real-time data of thermocouples and temperature set by user.
25
3.3.10 Relay:
2-Channel relay board is used to switch the coils in furnace. The Board connects
to Arduino via single (IN1, IN2). It accepts PWM signal to trigger the
electromagnetic in the relays. It requires VCC of 5V and also has JD-VCC if
relay board is used for switching AC or high DC voltages.
Figure 3. 14: Relays
3.3.11 Potentiometer:
5 Kilo Ohm variable resistor is used to control the temperature of furnace. It
connects to Arduino via analogue pin. 5 Kilo ohm potentiometer is used for
higher resolution. The potentiometer has range from 0 to 1023 which is later
converted in C++ based program to 101 to 298 using function name map.
Figure 3. 15: Potentiometer
26
CHAPTER 4
WORKING AND
DISCUSSION
27
4.1 PREVIEW:
A device was constructed which is capable of measuring Seebeck at high
temperatures. Previously available apparatus can measure Seebeck at
temperature range up to 60-70°C. Our device easily achieved the temperature
up to 300°C-330°C. For instance, we maintained the temperature of device till
300°C electronically.
4.2 WORKING
4.2.1 Temperature Difference:
Starting with Peltier for having temperature difference two Peltiers are attached
to heat sink and the sample holder where the sample which has to be tested is
placed. Heat sink is added to remove excess heat. For measuring temperature
difference two K-type thermocouples are attached to both Peltier as shown in
chapter 3. The sample holders are secured with Peltiers using thermal paste to
minimize induced currents.
4.2.2 High Temperatures:
To achieve high temperature three coils have been added to a furnace. Keeping
in mind that we have to construct a device that is portable so only the metal
body that is constructed covers only the area of sample holder and around its
sides coils are attached.
4.2.3 ELECTRONICS:
We connected VCC pins of MAX6675, ST7789 TFT IPS display and
potentiometer to 5V port of Arduino.

The SCL pin was connected to Pin 13

The SDA pin was connected to pin 11

The RST pin was connected to pin 8

The DC pin was connected to pin 7

The Max 6675 boards were daisy chained with their SO and SCK pins
connected to pin 12 and pin 19 respectively
28
The CS pins have to be unique so thy were connected to 3,4,5 pins. Relay IN1
pin was connected to 2 pin while potentiometer's middle pin was connected to
A1. The GND pins of MAX6675, ST7789 TFT IPS display and potentiometer
are connected to GND pin on Arduino board.
JD-VCC is used to turn on relay boards as in case of opto- coupler failure the
Arduino board doesn't gets damaged. JD-VCC and GND pins are connected to
power supply.
4.2.4 Code:
Nightly build version of Arduino IDE was used to write code for all the above
mentioned components. It is based on C++ language but is altered and
optimized for Arduino boards. This lets the Arduino board communicate with
all the mentioned components. The data recorded by the sensors can also be
exported in excel file if Arduino board is connected to computer. A software
named Tera Term can be used to log the data and further export it. The code is
as follows.
#include <Adafruit_ILI9341.h>
/*
ST7789 240x240 IPS (without CS pin) connections (only 6 wires required):
#01 GND -> GND
#02 VCC -> VCC (3.3V only!)
#03 SCL -> D13/PA5/SCK
#04 SDA -> D11/PA7/MOSI
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#05 RES -> D9 /PA0 or any digital
#06 DC -> D10/PA1 or any digital
#07 BLK -> NC
*/
#include <SPI.h>
#include <Adafruit_GFX.h>
#if (__STM32F1__) // bluepill
#define TFT_DC
PA1
#define TFT_RST PA0
//#include <Arduino_ST7789_STM.h>
#else
#define TFT_DC
7
#define TFT_RST 8
#include <Arduino_ST7789_Fast.h>
#endif
#define SCR_WD 240
#define SCR_HT 240
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Arduino_ST7789 lcd = Arduino_ST7789(TFT_DC, TFT_RST);
// define what kind of fonts should be used
#define USE_RRE_FONTS 1
#if USE_RRE_FONTS==1
#include "RREFont.h"
#include "rre_term_10x16.h"
#include "rre_bold13x20.h"
#include "rre_bold13x20v.h"
#include "rre_bold13x20no.h"
RREFont font;
// needed for RREFont library initialization, define your fillRect
void customRect(int x, int y, int w, int h, int c) { return lcd.fillRect(x, y, w,
h, c); }
#else
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#include "PropFont.h"
#include "bold13x20digtop_font.h"
#include "term9x14_font.h"
PropFont font;
// needed for PropFont library initialization, define your drawPixel and
fillRect
void customPixel(int x, int y, int c) { lcd.drawPixel(x, y, c); }
void customRect(int x, int y, int w, int h, int c) { lcd.fillRect(x, y, w, h, c); }
#endif
#include "max6675.h"
#include <Wire.h>
int thermoDO = 12;
int thermoCS = 3;
int thermoSCK =19 ;
MAX6675 thermocouple1(thermoSCK, thermoCS, thermoDO);
float tempF=0;
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int thermo2DO = 12;
int thermo2CS = 4;
int thermo2SCK =19 ;
MAX6675 thermocouple2(thermo2SCK, thermo2CS, thermo2DO);
float tempC=0;
int thermo3DO = 12;
int thermo3CS = 5;
int thermo3SCK =19 ;
MAX6675 thermocouple3(thermo3SCK, thermo3CS, thermo3DO);
float tempH=0;
const int RELAY_PIN = 2;
int vccPin = 3;
int gndPin = 2;
int POTENTIOMETER_PIN = A1;
int dt;
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//-----------------------------------------------------------------------------
void setup()
{
Serial.begin(9600);
pinMode(vccPin, OUTPUT); digitalWrite(vccPin, HIGH);
pinMode(gndPin, OUTPUT); digitalWrite(gndPin, LOW);
delay(1);
lcd.init(SCR_WD, SCR_HT);
#if USE_RRE_FONTS==1
font.init(customRect, SCR_WD, SCR_HT); // custom fillRect function and
screen width and height values
#else
font.init(customPixel, customRect, SCR_WD, SCR_HT); // custom
drawPixel and fillRect function and screen width and height values
#endif
}
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const uint16_t lnCol = RGBto565(255,154,0);
const uint16_t ln2Col = RGBto565(180,180,180);
const uint16_t labCol = RGBto565(255,255,255);
const uint16_t v1Col = RGBto565(255,0,0);
const uint16_t v2Col = RGBto565(0,161,255);
const uint16_t v3Col = RGBto565(55,255,0);
const uint16_t v4Col = RGBto565(255,120,120);
const uint16_t v5Col = RGBto565(150,150,255);
//const uint16_t v5Col = RGBto565(250,150,250);
int mode=0,lastMode=-1;
void setBigNumFont()
{
#if USE_RRE_FONTS==1
font.setFont(&rre_Bold13x20v);
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//font.setFont(&rre_Bold13x20); // regular RRE rendered with rectangles
//font.setFont(&rre_Bold13x20no); // like above but no overlapping
#else
font.setFont(Bold13x20);
#endif
font.setSpacing(1);
font.setScale(1,2);
font.setDigitMinWd(16);
}
void setInfoFont()
{
#if USE_RRE_FONTS==1
font.setFont(&rre_term_10x16);
#else
font.setFont(Term9x14);
#endif
}
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void drawField(int x, int y, int w, int h, char *label, uint16_t col=lnCol)
{
lcd.drawRect(x,y+7,w,h-7,col);
setInfoFont();
font.setScale(1);
font.setColor(labCol,BLACK);
int wl = font.strWidth(label);
font.printStr(x+(w-wl)/2,y,label);
}
void showVal(float v, int x, int y, int w, int p, uint16_t col)
{
setBigNumFont();
font.setColor(col,BLACK);
char txt[10];
dtostrf(v,w,p,txt);
font.printStr(x,y,txt);
}
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void constData()
{
drawField(
0, 0,120,80-2,"Cold Side",v2Col);
drawField(120+5, 0,120-5,80-2,"Hot Side",v1Col);
drawField( 0, 81,240,80-2,"Furnace Temperature",v3Col);
drawField( 0,162,240,80-2,"Set Temperature",lnCol);
setBigNumFont();
int wv=font.strWidth("88.8");
font.setColor(v2Col); font.printStr(32+wv,0+24,"'$");
font.setColor(v1Col); font.printStr(155+wv,0+25,"'$");
wv=font.strWidth("88.8");
font.setColor(v3Col); font.printStr(155+wv,82+25,"'$");
wv=font.strWidth("999999999.99");
font.setColor(lnCol); font.printStr(22+wv,162+25,"'$");
wv=font.strWidth("888.8");
int wv2=font.strWidth("888");
setInfoFont();
font.setScale(1,2);
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}
void loop(){
loop1();
loop2();
loop3();
}
void loop1() {
tempF = thermocouple1.readCelsius();
delay(50);
Serial.print("temp1");
Serial.println(tempF);
tempC = thermocouple2.readCelsius();
delay(50);
tempH = thermocouple3.readCelsius();
delay(50);
return tempF,tempC,tempH;
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}
void loop2() {
dt = analogRead(A1);
dt = map(dt, 0, 1023, 99, 305);
analogWrite(9, dt);
int analogValue = analogRead(POTENTIOMETER_PIN);
if(tempF > dt)
digitalWrite(RELAY_PIN, HIGH); // turn on Relay
else
digitalWrite(RELAY_PIN, LOW); // turn off Relay
delay(50);
return dt;
}
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void varData()
{
//v1=88.8; v3=8888.8; v4=888.8; v5=8888888.88;
// PropFont optimizing: noopt=350ms, ff=317ms, 0+ff=298ms, +f0=290ms
+0f=277ms
showVal(tempC, 15,0+24, 3,1, v2Col);
showVal(tempH, 15+120,0+24, 3,1, v1Col);
showVal(tempF,22,82+24, 9,1, v3Col);
showVal(dt, 10,162+25, 9,0, lnCol);
}
void loop3 ()
{
if(mode!=lastMode) {
lastMode=mode;
lcd.fillScreen(BLACK);
constData();
}
varData();
delay(1); }
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4.3 MEASUREMENT METHODOLOGY
Two methods can be used by to measure the seebeck coefficient using this
device which are integral method and differential method.
In integral method one parameter is fixed while the other is varied with time to
measure quantities. In our case, either the hot or cold side is fixed and the latter
can be varied.
Our Device is capable of performing measurements using both methods.
4.4 RESULTS AND DISCUSSION
Due to on-going situation (Covid-19) and closure of Laboratories in university
we could not get a sample to test our device. Nevertheless, we tested our
device’s range which is:

Hot side ~ 160°C

Cold side ~ 50°C

Furnace Temperature = 331°C
4.5 CONCLUSION
A simple device is fabricated to measure Seebeck coefficient at high
temperatures of samples having cylindrical or disc shape. The device
constructed is made from components which are easily available in market and
are of high quality to ensure minimum errors while measuring. The device uses
simple electronics which are reliable for measuring sensitive data accurately.
Unfortunately, due to prevailing situation we were unable to test our device, yet
this device would enable to measure Seebeck coefficient of metals under high
temperatures which would help observe the behavior of material at temperatures
higher than room temperature.
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REFERENCES
1.
Helmut Werheit et al 2009 J. Phys.: Conf. Ser.176 012037.
2.
J. Martin, T. Uher, J. Appl. Phys. 108, 108, 121101 (2010).
3.
https://aip.scitation.org/doi/am-pdf/10.1063/1.4934577.
4.
https://pdfs.semanticscholar.org/f921/941a6b3a13180adef3ff593d591d0
8875835.pdf.
5.
http://www.kirj.ee/public/Engineering/2007/issue_4/eng-2007-4-2.pdf.
6.
http://news.mit.edu/2010/explained-thermoelectricity-0427.
7.
https://www.nature.com/articles/nmat2090.
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