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International University
Biomedical Engineering Department
DESIGN AND DEVELOPMENT OF A
LABORATORY THERMOSTATIC WATER BATH
By
Doan Tin Duc
BEBEIU16041
A thesis submitted to the School of Biomedical Engineering in partial fulfillment of the
requirements for the degree of Engineer
Ho Chi Minh City, Vietnam
August – 2020
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DESIGN AND DEVELOPMENT OF A
LABORATORY THERMOSTATIC WATER BATH
APPROVED BY:
________________________________ ,
Pham Thi Thu Hien, Assoc. Prof., Advisor
________________________________ ,
Vo Van Toi, Prof., Chair
______________________________
Nguyen Thanh Tam, Ph.D., Reviewer
______________________________
Pham Thi Thu Hien, Assoc. Prof.,
Member
______________________________
Ngo Thanh Hoan, Dr., Member
______________________________
Ngo Thi Lua, Dr., Secretary
THESIS COMMITTEE
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ACKNOWLEDGEMENTS
First and foremost, I would like to express my greatest gratitude to Mrs. Pham Thi Thu
Hien, my advisor who guided me through this thesis with her useful advices, feedbacks,
and encouragements. I would not be able to come this far without her dedication and
kindness, which motivated me to improve even further.
I would like to give my thanks to Mr. Nguyen Le Y, for inspired me to start this project
and helped me materialize my ideas. There were some difficult problems I would never
work out myself if not for his knowledges and enthusiasm.
Furthermore, I want to thank Mr. Do Tuan Anh, Ms. Nguyen Le Hoang Cam, Ms. Ha
Nguyen Yen Nhi, Mr. Tran Hong Gia Bao, and Ms. Lam Khanh Van for staying by my
side through thick and thin, aiding me in different problems, both in school and in life. It
was thanks to them that my life in university was so enjoyable.
I want to give my thanks to all my friends in my department, who accompanied with
me through difficult times when doing our thesis together, for supporting me whenever I
need them, no matter how big or small.
Finally, I want to show my deepest gratitude to my family, who raised me to be the
person I am now and gave me unconditional love and support. Thank you for being my
source of power to face and overcome any difficulties or challenges. I would never achieve
this accomplishment without them.
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................................ 3
TABLE OF CONTENTS .................................................................................................... 4
LIST OF FIGURES ............................................................................................................ 8
LIST OF TABLES ............................................................................................................ 11
ABSTRACT...................................................................................................................... 12
CHAPTER I INTRODUCTION ....................................................................................... 14
1.1.
Problem statement .............................................................................................. 14
1.2.
Objectives and scope of the project.................................................................... 15
1.3.
Structure of the thesis report .............................................................................. 15
CHAPTER II LITERATURE REVIEW .......................................................................... 17
2.1.
Different methods in temperature control .......................................................... 17
2.1.1.
Electric heating ........................................................................................... 17
2.1.2.
Vapor compression refrigeration ................................................................ 17
2.1.3.
Thermoelectric cooling ............................................................................... 18
2.2.
Current commercialized products ...................................................................... 20
2.2.1.
Memmert Water Bath WNB 7 .................................................................... 20
2.2.2.
PolyScience Cryoprecipitate Bath .............................................................. 21
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2.2.3.
2.3.
Julabo Shaking Water Bath ......................................................................... 22
Practical applications of the laboratory water bath ............................................ 23
2.3.1.
Plasma ......................................................................................................... 23
2.3.2.
Preparation process ..................................................................................... 25
2.4.
Design requirements ........................................................................................... 25
2.4.1.
Specification ............................................................................................... 25
2.4.2.
Decision matrix ........................................................................................... 27
CHAPTER III METHODOLOGY ................................................................................... 29
3.1.
Principle of Thermoelectric effect in temperature control ................................. 29
3.2.
PID controller in temperature control ................................................................ 30
3.2.1.
Overview ..................................................................................................... 30
3.2.2.
PID value .................................................................................................... 31
3.3.
System components and operation ..................................................................... 32
3.3.1.
System components .................................................................................... 32
3.3.2.
System operation ......................................................................................... 36
3.4.
Hardware development: ..................................................................................... 37
3.5.
Software implementation: .................................................................................. 46
3.5.1.
PID algorithm.............................................................................................. 48
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3.5.2.
Pulse width modulation control .................................................................. 49
3.5.3.
LCD display ................................................................................................ 50
3.6.
Experiment procedures ....................................................................................... 51
3.6.1.
Accuracy test ............................................................................................... 51
3.6.2.
Plasma test .................................................................................................. 52
CHAPTER IV RESULTS ................................................................................................. 54
4.1.
Final product ...................................................................................................... 54
4.2.
Experiments on the thermostatic water bath system .......................................... 57
4.2.1.
Thermocouple testing.................................................................................. 57
4.2.2.
Plasma samples testing ............................................................................... 59
4.3.
Device comparison ............................................................................................. 61
CHAPTER V DISCUSSION AND IMPLEMENTATIONS ........................................... 63
5.1.
Beneficial features .............................................................................................. 63
5.2.
Shortcomings...................................................................................................... 64
5.3.
Implementations ................................................................................................. 65
CHAPTER VI CONCLUSION ........................................................................................ 66
REFERENCES ................................................................................................................. 67
APPENDIX SOFTWARE CODE SCRIPT ...................................................................... 70
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LIST OF FIGURES
Figure 1: A simple vapor compression refrigeration cycle ............................................... 18
Figure 2: Memmert Peltier cooling device ....................................................................... 19
Figure 3: Memmert's Water bath WNB 7 ......................................................................... 20
Figure 4: Sketch of the Water bath WNB 7 ...................................................................... 21
Figure 5: PolyScience Cryoprecipitate bath ..................................................................... 22
Figure 6: Julabo SW22 Shaking Water Bath .................................................................... 23
Figure 7: Blood components [10] ..................................................................................... 24
Figure 8: Schematic of a thermoelectric couple [6]. ......................................................... 29
Figure 9: Arduino Uno Rev3 ............................................................................................ 33
Figure 10: DS18B20 digital thermocouple ....................................................................... 33
Figure 11: IBT-2 H-Bride module .................................................................................... 34
Figure 12: TEC1-12710 Peltier module............................................................................ 34
Figure 13: AVC heatsink .................................................................................................. 35
Figure 14: Lock&Lock LLG205 ....................................................................................... 35
Figure 15: DC power supply ............................................................................................. 36
Figure 16: Flowchart of the water bath system ................................................................. 37
Figure 17: Aluminum heatsink and DC power source...................................................... 38
Figure 18: First version of the device with 2 electric fans on the sides ............................ 39
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Figure 19: First version of the device with the heat-resistant glass bath .......................... 39
Figure 20: New heatsink with the prototype thermal insulation chamber ........................ 40
Figure 21: Side view of the heatsink................................................................................. 41
Figure 22: 8x8cm rectangular holes through both side of the case................................... 42
Figure 23: The barrier covered with polyethylene foam .................................................. 43
Figure 24: The barrier was made to fit perfectly with the heatsink and case ................... 43
Figure 25: The thermal insulation chamber ...................................................................... 44
Figure 26: The lid and the body connected by a hinge ..................................................... 45
Figure 27: Solidworks sketch for the case of the circuit ................................................... 45
Figure 28: Flowchart of the control system ...................................................................... 47
Figure 29: Schematic of the controlling circuit ................................................................ 48
Figure 30: Pulse width modulation [23] ........................................................................... 50
Figure 31: Information menu ............................................................................................ 51
Figure 32: Mode select menu ............................................................................................ 51
Figure 33: Temperature set menu ..................................................................................... 51
Figure 34: Pro'sKit MT-1706 and the thermocouple ........................................................ 52
Figure 35: V-730 UV-Visible Spectrophotometer ............................................................ 53
Figure 36: Plasma samples labeled from A to C (left to right, respectively).................... 53
Figure 37: Front view of the final product ........................................................................ 54
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Figure 38: Top down view of the final product ................................................................ 55
Figure 39: Front view of the control panel ....................................................................... 55
Figure 40: Back view of the control panel ........................................................................ 56
Figure 41: Power outlet of the DC supply ........................................................................ 56
Figure 42: Measuring sensor readings .............................................................................. 59
Figure 43: UV-VIS absorption of sample A (top) in comparison to sample B (bottom) . 60
Figure 44: UV-VIS absorption spectrum of sample A (top) in comparison to sample C
(bottom)............................................................................................................................. 61
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LIST OF TABLES
Table 1: Requirements for the device ............................................................................... 27
Table 2: Development board ............................................................................................. 27
Table 3: Temperature sensor ............................................................................................. 28
Table 4: Peltier module ..................................................................................................... 28
Table 5: Temperature readings ......................................................................................... 57
Table 6: Paired Samples Test by T-test ............................................................................ 58
Table 7: Sample thawing time .......................................................................................... 59
Table 8: Device specifications comparison ...................................................................... 62
Table 9: Comparison with WNB7 and SW22 water bath model ...................................... 62
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ABSTRACT
In laboratory, thawing or heating process can be a very difficult problem such as many
operating procedures require specific temperature to carry out. Hence, a water bath is
needed for indirect temperature control by adjusting the temperature of the intermediate
environment such as water. In this study, the thermostatic water bath based on
thermoelectric effect (e.g. Peltier effect, Seebeck effect…) was designed, calibrated and
examined with plasma samples. The device in this project used thermoelectric cooler
(TEC) to maintain and control the setting temperature of a container made of heat-resistant
glass. The system was then put inside a thermal-insulated chamber to prevent exchanging
heat with the environment. The electrical system included an Arduino UNO
microcontroller, an IBT-2 H-bridge motor driver module, and a DS18B20 temperature
sensor. To improve the stability of the temperature, PID algorithm was applied into the
program. The temperature value inside the container is collected real-time through the
sensor and displayed on the LCD panel. The TEC is driven by an IBT-2 module which is
controlled by the Arduino through PWM signal. The performance and accuracy of the
system was calibrated with an industrial thermocouple sensor (Pro’sKit MT-1706), and
then tested with plasma samples. The experimental results showed that the accuracy of the
device had positive results with the error of ±0.3oC. Moreover, the plasma samples also
had significant improvement in thawing time in comparison with thawing at room
temperature (by an average of 65%). Using the UV-VIS spectrophotometer, the spectra of
the samples also exhibited no difference between two thawing methods. In conclusion, the
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system will aid in different preparation processes in the laboratory and greatly reduce the
time consumed. In the future, the system can be further developed to have more function
such as timer, adjustable rising time, and wireless control.
Keywords: water bath, thermoelectric cooling, Peltier effect, Arduino Uno, PID
algorithm.
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CHAPTER I
INTRODUCTION
1.1.Problem statement
Cold storage and cryopreservation are among the most common forms of storing and
maintaining organic samples. When the sample’s temperature is reduced, biological and
chemical reactions are also slowed down, resulting in longer storing time. Furthermore,
keeping the sample at low temperature environment is also aimed to prevent any harmful
germs from growing and damaging it. However, thawing or raising their temperature to a
usable or specific condition is another concern. In laboratory, there are some experiments
that require a specific temperature, or preparation procedures including proteins or
materials that have unique melting or freezing points. In blood transfusion, where fresh
frozen plasma (FFP) and plasma frozen within 24 hours (PF24) are widely used, the
samples are required to be defrosted before transfusing. Hence, a safe and quick method
for thawing is much needed, and a water bath is a device that can satisfy all the
requirements.
In the recent years, the need of developing more compact, portable cooling technology
has gathered a lot of attention of many manufacturers, and thermoelectric cooling is one of
the emerging methods in thermal control. What makes thermoelectric cooling really stand
out among others cooling methods is its effectiveness when operating in a very limited
space with low energy consumption. Many companies have developed different devices
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based on thermoelectric cooling. In laboratory, a thermoelectric-based water bath is a
perfect device that can offer a wide range of applications within a very small area.
1.2.Objectives and scope of the project
This project aimed to develop a thermostatic water bath using thermoelectric effect,
which is a phenomenon where temperature difference is created by applying a current to
the intersection between two different materials [1]. This effect is utilized as a method of
controlling the temperature of the water bath. A closed-loop PID temperature control
system is implemented using an Arduino Uno, a DS18B20 thermocouple, and a TEC112710 Peltier module driven using IBT-2 H-Bridge module.
The final product is a water bath system with simplified and straightforward control.
The heat insulation chamber shows positive results in increasing the efficiency of the
system. Throughout different tests, the water bath exhibits significant improvement in
thawing time in comparison to leaving the samples at room temperature. However, the PID
controller of the system still need to be working on since instantaneous transition between
heating and cooling is not possible. The water bath holds a lot of potential for further
developments such as modifying rising time, timer, or wireless controlling.
1.3.Structure of the thesis report
According to the information, the structure of the thesis report is explained below:
-
Chapter II provides general information on common methods of temperature
control, current commercialized products, and practical applications.
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-
Chapter III gives details on how the system is designed: its principle, hardware, and
software development.
-
Chapter IV exhibits the results of the device, and how it performed.
-
Chapter V gives insights on the results and discussion for further upgrades and
developments.
-
Chapter VI gives conclusion on the project including the potentials in the future
-
The appendix shows the script for the Arduino code and decision matrices.
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CHAPTER II
LITERATURE REVIEW
2.1.Different methods in temperature control
2.1.1. Electric heating
Electric heating is famous for its straightforward applications in different fields that
require high temperature such as water heating, welding… It is a process where a heating
element radiates heat when electric current is applied [2]. Although fuel combustion is
more energy-efficient, but electric heating is more generally applied due to its compactness
and cleanliness. The downside of this method is its inability to operate below ambient
temperature.
2.1.2. Vapor compression refrigeration
Vapor compression refrigeration system is one of the most common method for
cooling. A typical system is made of an evaporator, a compressor, a condenser, and an
expansion valve (Figure 1). Principle of the system is described below [3], [4]:
-
Refrigerant start from a low pressure and temperature gas state. It is then
compressed and enters high pressure, high temperature state.
-
In the next phase, the refrigerant enters the condenser and exchange heat with a
secondary fluid which has a lower temperature and become liquid state.
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-
The liquid refrigerant enters the expansion valve and undergoes Joule-Thompson
effect, which cause the refrigerant to partially evaporate and exit the valve in low
pressure and temperature (liquid vapor mixture) state.
-
The refrigerant then enters the evaporator where the refrigerant has lower
temperature than the environment, causing it to vaporize, resulting in the cooling
effect of the environment.
Qc
Condenser
Expansion
Compressor
valve
Evaporator
Qe
Figure 1: A simple vapor compression refrigeration cycle
2.1.3. Thermoelectric cooling
Thermoelectric cooling is an emerging technology in temperature control and has been
developing ever since the establishment of thermoelectric material science [5]. A
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thermoelectric cooler functioned as a heat pump that when provided with an electric
current, heat is transferred from one side of the cooler to the other [6]. Comparing to
conventional cooling, Depending on different scenarios and how it is applied,
thermoelectric cooling can have very distinctive benefits, such as [7], [8]:
-
Freely alternate between heating and cooling by controlling the direction of
the electric current.
-
Noise-free and vibration-free.
-
Require less maintenance.
-
Operating regardless of position.
With its advantages outweigh disadvantages, thermoelectric cooling device could
become a very promising field in the future.
Figure 2: Memmert Peltier cooling device
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2.2.Current commercialized products
Many medical corporations have developed a lot of water bath with different types and
functions suitable for every need in the laboratory. This thesis introduced three types of
typical water bath for general use in the laboratory.
2.2.1. Memmert Water Bath WNB 7
Memmert is one of the most well-known corporation in developing laboratory
equipment and especially water bath and oil bath. One of their products is the WNB 7
(Figure 3, 4).
Figure 3: Memmert's Water bath WNB 7
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Figure 4: Sketch of the Water bath WNB 7
The WNB 7 is a general-use laboratory water bath with working range from 5oC up to
95oC above ambient (room) temperature. The reservoir is made with stainless steel provide
highest quality of sturdiness and reliability. The water bath also provides heating on all
surface which improve the temperature uniformity and heating efficiency.
2.2.2. PolyScience Cryoprecipitate Bath
PolyScience is famous in manufacturing different types of baths such as refrigerated
circulating bath, recirculating coolers, water baths… Figure 5 is their cryoprecipitate water
bath.
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Figure 5: PolyScience Cryoprecipitate bath
The device is made specifically to prepare for retrieving cryoprecipitated
antihemophilic factor (also known as cryoprecipitate) by thawing fresh frozen plasma at
4oC. The bath can maintain the temperature at fixed setpoint 4oC with high accuracy at
±0.1oC.
2.2.3. Julabo Shaking Water Bath
Shaking water bath is one of the essential equipment in the laboratory, especially in
cell laboratories. A shaking water bath can aid in growing cell culture or mixing and heating
simultaneously.
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Figure 6: Julabo SW22 Shaking Water Bath
Julabo shaking water bath SW22 (Figure 6) working temperature ranging from 20oC to
99.9oC above ambient temperature with an accuracy of ±0.2oC. Also, the shaking
frequency can be freely adjusted between 20 and 200 RPM.
2.3.Practical applications of the laboratory water bath
2.3.1. Plasma
Plasma is a part of the blood component, along with red blood cells, white blood cells,
and platelets (Figure 7). Plasma is used in treatment for severe bleeding and disseminated
intravascular coagulation since it contains high concentration of blood clotting factors and
other elements [9].
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Figure 7: Blood components [10]
Usually, plasma is stored by freezing at -18oC or lower after collected. Plasma that is
frozen around 6 to 8 hours after collected is called fresh frozen plasma (FFP), and plasma
that is frozen within 24 hours after collected is called plasma frozen within 24 hours (FP24),
both are stored at -18oC or lower. Comparing to FFP, FP24 has reduced FV and FVIII [9],
however, FP24 has the same usability except for cases that specifically need to replace FV
or FVIII.
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2.3.2. Preparation process
Before plasma is used in experiments or transfusion, a water bath is required in different
procedures of thawing plasma depending on the scenario. Usually, a unit of plasma
between 210-250ml can be thawed in the water bath of 37oC in 45 minutes when put in a
plastic bag [11]. After the plasma is thawed, it should be stored at 1-6oC for no more than
4 days or the quality of clotting proteins would suffer. Another application of the water
bath in plasma preparation is cryoprecipitate manufacturing. In this process, FFP is thawed
in the water bath between 1oC to 6oC and is then centrifuged for cryoprecipitate retrieval
[12].
2.4.Design requirements
2.4.1. Specification
In this thesis, there are some aspects that the design must consider for maximized
efficiency and suitable for the project. Such requirements are:
•
•
•
•
•
Working principle
Size
Working temperature range
Power
Rising time (time required for the temperature to reach setpoint)
The device is designed for laboratory general use; therefore, it should be portable and
able to cover a wide temperature range. There were different methods of thermal control
introduced in this report. One of them is electric heating, a simple form of heating which
comes in all kinds of sizes suitable for different purposes. The downside of electric heating
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is that it cannot work below ambient temperature. Another method is vapor compression
refrigeration which would greatly increase the cost and complexity of the device, also, it is
hard to maintain the desired compactness. On the other hand, thermoelectric cooling, which
is based on Peltier effect, is the most suitable method since it can behave as both heating
and cooling unit. What makes thermoelectric cooling superior in this scenario is that it can
operate even in a very limited space while requires little to no maintenance.
This project aimed to aid in the plasma preparation process, such as thawing or
preparing cryoprecipitate. Usually, plasma is thawed at 30-37oC [13], or even 56oC in
emergency cases [11](e.g. transfusion), and 4oC for cryoprecipitate retrieval. Therefore,
the temperature range of the device should be able to heat up to 56oC and cool down to
4oC. Since most commercialized models have the accuracy of ±0.2 or lower, this was used
as a reference point for the device. Plasma samples are stored in vacutainer or Eppendorf
tube ranging from 0.5ml to 10ml or higher, a bath size of 500ml should be able to provide
enough room for the operation while maintaining a minimum place.
The rising time of the bath should match with the required time for any prior
preparation process such as retrieving the samples from the freezer. In the author’s
laboratory, this process may take up to 20 minutes, hence the rising time of the bath should
fall within this period. This left us with the last problem, which was the heating power. The
device should be able to provide enough heat to raise the temperature of 150ml water (about
one-third the volume of the bath) from 24oC (room temperature) to 56oC in 20 minutes,
which the minimum power required was 17W after calculation. Taken the heat conductance
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of the bath material into account, the power should be higher than expected. The
requirements for the device are described in the table below:
Table 1: Requirements for the device
Factor
Minimum temperature range
Rising time
Accuracy
Bath size
Minimum heating power
Value
4oC ~ 56oC
20 minutes
±0.2oC
500ml
17W
2.4.2. Decision matrix
The main components of the device are the development board, the temperature sensor,
and the thermoelectric module which directly affect the working operation. Therefore, to
select the right part and maximize the efficiency of the system, comparison between
different options was made using decision matrix method. In these matrices, each factor
was rated on the scale from 0 (bad) to 5 (excellent). The results are presented below:
Table 2: Development board
Factor
Price
Size
Power jack
Support libraries
Total
Mega
3
2
5
3
13
Uno
5
4
5
5
19
27
Nano
4
5
2
4
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Table 3: Temperature sensor
Factor
Temperature range
Accuracy
Communication
Price
Total
RTD K-type
3
4
3
4
14
DS18B20
4
3
5
5
17
PT100
5
5
3
2
15
Table 4: Peltier module
Factor
Power
Current required
Heatsink required
Price
Total
12706
3
4
5
5
17
12710
4
5
5
4
18
28
12712
4
4
4
4
16
12715
5
3
3
3
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CHAPTER III
METHODOLOGY
3.1.Principle of Thermoelectric effect in temperature control
The research on temperature controlling technology has been widely studied since it
plays an irreplaceable role in daily life such as preparation or preservation procedures. In
this regard, thermoelectric cooling has proved effective in localized operations for having
no moving part or circulating fluid [14]. With its advantages outshine disadvantages,
thermoelectric cooling has been widely utilized in different fields such as refrigeration,
aviation, and laboratory applications.
The definition of thermoelectric effect is the absorption of heat through the conjunction
of two conductors (Figure 8) [7]. The heat absorbed can be controlled by modifying the
Figure 8: Schematic of a thermoelectric couple [6].
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direction and power of the electric current. With the material used for the module, the heat
can be determined:
𝑸𝛱 = (𝛱1 − 𝛱2 )𝑱
(1)
Where Π1,2 are the material’s Peltier coefficients, and 𝑱 is the current density.
Thermoelectric devices operate on DC current, which makes it easier to control its
behavior by modifying the input current. Provided with how the output of the device can
be controlled to either heating or cooling and utilizing the PID controller, a constant and
precise temperature can be achieved [15].
3.2.PID controller in temperature control
3.2.1. Overview
Proportional-Integral-Derivative (PID) is a controlling algorithm that has become
universally applied in different fields that require precise response, both personal and
industrial use for its versatility and effectiveness in most controlling process.
The PID controller is used in a feedback loop control system where it adjusts the
process variable to match a setpoint, or a desired value. A PID controller processes upon
the difference between the process variable and the setpoint, also known as “error”, after
and attempts to minimize it after each loop by modifying the output according to the signal
received. A PID controller works on three parameters, with their own specific roles and
characteristics: Proportional, Integral, and Derivative.
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3.2.2. PID value
Each term of the PID controller has their own function and effect on the output of the
system, a detail explanation is provided below[16], [17]:
Proportional: the proportional value (or P-term) decides how aggressive the system
reacts to the instantaneous value of the system’s error. However, there exists a limit that
the error is too insignificant when reaching closer to the desired value that the system
cannot trigger enough output for the process variable to meet the setpoint, which is called
“steady state error”. Even if the proportional value is set large enough so the setpoint can
be met, it would cause the system to be unstable and oscillations will occur. Therefore, the
performance of a proportional controller is very limited in most systems.
Integral: the integral term (or I-term) of the PID controller tracks the difference of the
process variable and setpoint over time and compensate the controller’s output with the
value that proportional to the accumulated error, which also force the steady state error to
zero. The integral value is crucial because it enables the P-only controller to reach setpoint.
Although the integral value makes up for the steady state error of the P-only controller, it
also enhances the disturbance in the output. This means that if the system has very little
overshoot in the output can cause a huge spike in the system, resulting in a longer time for
the system to stabilize. In a very sensitive system, unsuitable integral value can heavily
damage the structure of the system.
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Derivative: derivative term (or D-term) takes the derivative of the system’s process
variable over time and compensating the output variable with significant adjustments when
the system detects errors in high frequency. This acts as a counteracting method for the
overshoot by negating any spikes or sudden changes during the system’s operation.
Although derivative term works very effective in dampening the output signal, it can
become a source of disturbance in the output in response to setpoint change or noise from
measuring process. It is necessary to ensure that Proportional and Integral term are enough
for the system as using Derivative term can increase the complexity in the tuning process
and causing the system to be more noise sensitive.
3.3.System components and operation
3.3.1. System components
The system consists of an Arduino Uno R3, an IBT-2 H-Bridge module, a TEC1-12710
Peltier module, heatsink for the Peltier module, and DC power source. Below are images
and detailed description of the system:
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3.3.1.1.Main processing unit
-
Microcontroller: ATmega328P
-
Operating voltage: 5V
-
Work as the main processing unit for the
PID controller.
Figure 9: Arduino Uno Rev3
3.3.1.2.Thermocouple
-
Voltage supply: 3~5V
-
Temperature range: -55oC to 125oC
-
Accuracy: ±0.5oC
-
Resolution: 9-bit to 12-bit
-
Interact through 1-Wire library.
Figure 10: DS18B20 digital thermocouple
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3.3.1.3.Driver module
-
Power supply: 6 ~ 27V
-
Control the direction and output of the
DC current to control the TEC module
through PWM channel of the Arduino.
Figure 11: IBT-2 H-Bride module
3.3.1.4.Peltier module
-
Voltage supply: 12V
-
Current supply: 10A
-
∆TMax: 67oC
-
QcMax: 105.8W
-
Serve as the heat source of the system.
-
Hot side and cool side of the module can
be inverted by changing the direction of
Figure 12: TEC1-12710 Peltier module
the current.
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3.3.1.5.Heatsink
-
Power supply: 12V
-
Prevent the hot side of the Peltier
module from rising too high and
damage the module.
Figure 13: AVC heatsink
3.3.1.6.Container
-
Size: 120x120x65mm
-
Heat-resistant glass.
-
Durable against sharp temperature
change.
Figure 14: Lock&Lock LLG205
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3.3.1.7.DC power supply
-
Voltage input: 220VAC
-
Voltage output: 9VDC~14VDC
-
Current output: 10A
Figure 15: DC power supply
3.3.2. System operation
The system’s working operation starts with the DS18B20 sensor reads the temperature
signal of the water inside the insulation chamber. The signal is collected by the Arduino to
control the IBT-2 module, which is connected to the DC power source, and the TEC112710 Peltier device. By controlling the PWM signal from Arduino, the output of the
Peltier module can be modified through the IBT-2 module in response to the temperature
signal of the sensor. The working operation of the device is described (Figure 16) below:
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Figure 16: Block diagram of the water bath system
3.4.Hardware development:
The design of the system has gone through a series of prototypes and improvements,
but in general, the water bath consists of a thermal insulation chamber, a Peltier-heatsink
system, and the controlling circuit.
The water bath was constructed to hold all the component together and sturdy enough
to prevent any outside force to affect the device. The main point of the design is to optimize
the efficiency of the heatsink by modifying airflow inside the system, which also maximize
the cooling power of the Peltier module since the performance of the cooling process
depends on the efficiency of the heatsink [18]. The case of the device is made of stainless
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steel, and the chamber is constructed with acrylic sheets. Details on how the device was
developed will be described below:
The first version of the device was designed to fit everything into the case; therefore, it
only consisted the case, aluminum heatsink with a 12-Volts electric fan (Figure 17), and
the heat-resistant glass container. After a test run, the minimum temperature could only
reach 24oC. Airflows inside the case was badly designed so the heat could not escape,
caused the walls of the case to heat up and increased the temperature even higher.
Therefore, two 12-volts electric fan was installed on the sides (Figure 18) to help
dissipating part of the residual heat. the insides were also covered with polyethylene foam
to prevent the sides from heating up. After the fan was installed, the temperature of the
Peltier module is stabilized (minimum temperature was 22oC), but it is still not enough for
the needs of the water bath.
Figure 17: Aluminum heatsink and DC power source
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Figure 18: First version of the device with 2 electric fans on the sides
Figure 19: First version of the device with the heat-resistant glass bath
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Hence, the heatsink was upgraded to another one that has better performance (Figure
20, 21). This heatsink comes with two 12-Volts electric fan offered superior heat
dissipation. Using the new heatsink, the Peltier module could reach the minimum
temperature of -10oC. This meant that the bath could even reach freezing point if there were
no heat exchanging activity with the environment.
Figure 20: New heatsink with the prototype thermal insulation chamber
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Figure 21: Side view of the heatsink
This left us with the airflow problem of the case since the power of the side fans was
not enough to manage all the heat inside and it would badly affect the overall performance
of the system. Therefore, rectangular holes of 8cm x 8cm (same size as the heatsink electric
fan) was created on both sides (Figure 22), forming an air passage through the case.
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Figure 22: 8x8cm rectangular holes through both side of the case
To ensure that the air is circulated the right way and to prevent any heat going inside
the system, a barrier made of acrylic was also installed. It enclosed the heatsink, forced the
air to travel along the case without leaving any excess heat entering the system. The barrier
was also covered with polyethylene foam to provide better heat prevention (Figure 23, 24).
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Figure 23: The barrier covered with polyethylene foam
Figure 24: The barrier was made to fit perfectly with the heatsink and case
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In order to achieve stable temperature and maximize efficiency, it is crucial to ensure
that the environment is excluded in the operation. Therefore, a thermal insulation chamber
plays an essential role in the system. In this project, the insulation chamber was designed
and constructed using acrylic and the interior was covered with polyethylene foam to
prevent escaping heat from the inside and exchanging heat with the outside (Figure 25).
Figure 25: The thermal insulation chamber
The chamber also came with a lid and was connected to the body by a hinge (Figure
26) for easier operation and to made sure that every components of the device was
connected to each other. Overall, the thermal insulation chamber was enough to sealed off
any thermal activity with the environment.
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Figure 26: The lid and the body connected by a hinge
Additionally, the case for the control circuit was designed using Solidworks to fix the
board onto the case (Figure 27). It also served the purpose of protecting the wires and
aesthetic.
Figure 27: Solidworks sketch for the case of the circuit
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3.5.Software implementation:
The software operation is a feedback loop control system where the Arduino Uno
records the temperature data from the DS18B20 sensors and calculates the value of the
offset of the reading from the setpoint, which is called “error”. Next, the error is processed
through PID algorithm with the output is the PWM signal. The output is then exported to
the IBT-2 H-Bridge module to drive the TEC1-12710 Peltier module with a 12V DC power
supply. The information on the current temperature, setpoint, and PWM signal of the
system are displayed through an LCD1602 LCD screen module. Also, users can interact
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with the device using a rotary encoder to change its setpoint, cooling or heating mode.
Figure 28 is the flowchart of the process and Figure 29 is the schematic of the system.
Figure 28: Flowchart of the control system
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Figure 29: Schematic of the controlling circuit
3.5.1. PID algorithm
PID algorithm is the key component that makes up all the controlling process. A welltuned PID controller can reduce errors and oscillations completely while maintaining a
desired rising time. PID algorithm operates on the “error”, which is a difference between
process value and setpoint. In this context, process value is the value of the real temperature
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and setpoint is the desired value of the water bath. After computing the error, the system
then proceeds to calculate the PID value [17], [19]:
𝜏
𝑑
𝑢(𝑡) = 𝐾𝑝 . 𝑒(𝑡) + ∫0 𝐾𝑖 . 𝑒(𝑡)𝑑𝑡 + 𝐾𝑑 . 𝑑𝑡 . 𝑒(𝑡)
(2)
Where Kp is the proportional term – it decides how aggressive the output responses to
the error, Ki is the integral term – a low-frequency compensator for steady-state error, and
Kd is the derivative term – a high-frequency compensator for short-term error.
Although derivative term can help minimize the time required for the system to
stabilize by reducing overshoot, it is more likely to add unnecessary complexity in tuning
process while having little to no impact on the performance in slow response system
[20](e.g. temperature control). Therefore, a PI-controller was enough for this project.
3.5.2. Pulse width modulation control
Pulse width modulation (PWM) is a method where pulses of various width is created
by switching digital signal on and off consecutively in a period. to simulate output that
resembles analog input [21]. These pulses are described by the ratio in percentage between
active time and inactive time of the signal in a period, this ratio is called “duty cycle”
(Figure 30). For example, a 50% duty cycle means that the digital signal is high for half a
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period and low for the other half, this also equals to an average of 50% of the maximum
voltage is transmitted for an analog input [22].
Figure 30: Pulse width modulation [23]
Therefore, an Arduino Uno can utilize PWM to control the MOSFET to adjust the
power source that go into the load. In this project, the load is the TEC and is driven by an
IBT-2 module, which consists of 2 MOSFETs connected in a H-bridge circuit, and a 12V
DC power source.
3.5.3. LCD display
The water bath also includes an LCD screen to display the information of the system
and the user can interact directly with the device using a rotary encoder located on the
control panel next to the LCD screen.
The LCD display contains 3 menus, which are information display menu (Figure 31),
“Mode select” (Figure 32), and “Set Temperature” (Figure 33). Mode select menu is where
user can change between heating and cooling mode. Since their operations run on different
sets of PID value so the user is required to manually select between the two. The “Set
Temperature” menu is where the user can select the set temperature by rotating the encoder,
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turning clockwise to increase the setpoint by 0.5oC and counterclockwise to decrease the
setpoint by 0.5oC. Finally, the information menu displays the current temperature in the
thermal insulation chamber, setpoint, and PWM signal from the Arduino.
Figure 31: Information menu
Figure 32: Mode select menu
Figure 33: Temperature set menu
3.6.Experiment procedures
3.6.1. Accuracy test
The accuracy of the water bath was tested using a thermocouple. The purpose of this
experiment was to examine if the sensor read the temperature correctly and how the system
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response to it. The thermocouple used in this project was the Pro’sKit MT-1706 (Figure
34).
Figure 34: Pro'sKit MT-1706 and the thermocouple
The test was carried out by changing the value of the temperature setpoint and measure
the temperature after the system stabilized. The temperature was recorded in the range of
12oC to 40oC with the increment of one unit. Cooling mode was set for setpoints below
room temperature and heating mode for setpoints above room temperature.
3.6.2. Plasma test
The practical performance of the water bath was tested using blood plasma, which was
taken directly from the author. The plasma samples were collected in vacutainer after
centrifuged and stored at -18oC freezer immediately after retrieval.
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The experiment was conducted by thawing plasma samples in two conditions: in the
water bath at 37oC and room temperature. After the plasma had completely defrosted, they
were diluted by 500 times and analyzed using the V-730 UV-Visible spectrophotometer
(Figure 35).
Figure 35: V-730 UV-Visible Spectrophotometer
The samples were labeled A, B, and C (Figure 36), sample A was thawed at room
temperature and the other two were thawed in the water bath at 37oC.
Figure 36: Plasma samples labeled from A to C (left to right, respectively)
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CHAPTER IV
RESULTS
4.1.Final product
After trying and different designs and improvements, the final product was constructed
and assembled with every component of the device firmly connected with each other. The
final look of the device is shown in Figure 37 and 38. The case for the control panel was
also 3D printed and fixed into the front of the device using M3 bolts and nuts (Figure 39,
40).
Figure 37: Front view of the final product
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Figure 38: Top down view of the final product
Figure 39: Front view of the control panel
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Figure 40: Back view of the control panel
Additionally, the cover for the power source is also 3D printed to protect the connection
with the device from exposing to the environment. The cover also comes with a 220V
power outlet socket and built-in switch and fuse (Figure 41) so the user can directly turn
the power on and off directly on the power source.
Figure 41: Power outlet of the DC supply
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4.2.Experiments on the thermostatic water bath system
4.2.1. Thermocouple testing
The whole process was repeated three times and the results is described in table 5 and 6.
Table 5: Temperature readings
o
Setpoint ( C)
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
(room
temperature)
27
28
29
30
31
32
33
34
35
36
37
Recorded
temperature
1st
(oC)
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Sensor readings (oC)
2nd
3rd
12.3
12.9
13.8
14.8
15.7
16.7
18
18.7
19.9
21
22.1
22.8
24.1
24.9
12
13.1
13.7
15.1
16.1
17
17.9
18.9
20.1
21.2
21.8
23
24.2
24.8
12.1
13
14.1
15.2
15.9
17.2
18
18.9
20
20.9
21.8
22.9
24.1
25
26
26.2
26.1
26.2
27
28
29
30
31
32
33
34
35
36
37
26.9
27.9
28.8
30
30.9
32
33
33.8
34.8
35.7
36.8
27
28.1
28.9
30.1
31
31.9
33.1
33.7
34.8
35.9
37.1
27.1
28
28.8
29.8
31
32
32.8
34.1
35
36.1
37.2
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38
39
40
38
39
40
38.1
38.9
39.8
38
38.8
40.1
38.1
38.8
40
Table 6: Paired Samples Test by T-test
Paired Samples Test
Paired Differences
Mean
Std.
Deviation
Record – 1st .09310
.15337
Record – 2nd .01724
.14160
rd
Record – 3 -.00345
.12951
Where recorded temperature
Std.
Error
Mean
95% Confidence
Interval of the
Difference
Lower
Upper
t
df
Sig.
(2tailed)
.02848 .03476
.15144 3.269 28
.003
.02629 -.03662
.07110 .656 28
.517
.02405 -.05271
.04582 -.143 28
.887
is the values measured by MT-1706, and sensor
readings is the value measured by the sensor of the water bath. The graphs of the sensor
readings comparing to the thermocouple are also provided for better illustration (Figure
42):
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Temperature (oC)
Biomedical Engineering Department
Comparison between thermocouple and device
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
6
Reference
1st evaluation
2nd evaluation
3rd evaluation
12
16
20
24
28
32
36
40
Measuring point
Figure 42: Measuring sensor readings
4.2.2. Plasma samples testing
After the experiment, the total thawing time and the UV-VIS absorption spectra of the
samples was recorded for comparison. The results of the experiment are presented below,
Table 7 is the thawing time of the sample and Figure 43 and 44 are their absorption spectra.
Table 7: Sample thawing time
Sample
A
B
C
Thawing time
14 minutes 2 seconds
5 minutes 20 seconds
4 minutes 30 seconds
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Figure 43: UV-VIS absorption of sample A (top) in comparison to sample B (bottom)
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Figure 44: UV-VIS absorption spectrum of sample A (top) in comparison to sample C
(bottom)
4.3.Device comparison
The device was compared with the requirements table in chapter 2 (Table 8) and other
commercialized product: the water bath model WNB7 (by Memmert), and the shaking
water bath model SW22 (by Julabo) (Table 9).
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Table 8: Device specifications comparison
Specification
Temperature range
Heating power
Rising time
Bath size
Accuracy
Requirements
4oC ~ 56oC
17W
20 minutes
500ml
±0.2
Final product
4oC ~ 70oC
92W
17 minutes
300ml
±0.3
Table 9: Comparison with WNB7 and SW22 water bath model
Specifications
Temperature range
Temperature accuracy
Bath size
Boiling mode
Cooling mode
Timer
Shaking mode
WNB7
+10oC ~ +95oC
±0.15
7l
Yes
No
Yes
No
SW22
+20oC ~ +99.9oC
±0.2
8l
Yes
No
Yes
Yes
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Final product
4oC ~ 70oC
±0.3
300ml
No
Yes
No
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CHAPTER V
DISCUSSION AND IMPLEMENTATIONS
5.1.Beneficial features
As can be seen from the temperature reading result, the water bath has exhibited
excellent accuracy in the test with the thermocouple. The controller of the system
responded to the sensor effectively with the accuracy of ±0.3oC. Additionally, the task of
calibrating the PI-term for the algorithm had been successfully carried out with an
acceptable rising time and stability. The device also showed significant improvement in
the thawing time of the samples (62% shorter for sample B and 68% shorter for sample C
in comparison to sample A which was at room temperature).
The UV-VIS test was to analyze the component of the samples after they are thawed,
by comparing the UV-VIS absorption spectra of the samples, it can be decided if the
samples were affected by rapid thawing using the water bath. Therefore, the spectra of the
plasma samples shown little to no significant difference. The most prominent features of
the spectra are the peaks in the range of 283nm and 295nm were maintained in both
conditions.
Comparing with the requirements in chapter 2, the final product has achieved almost
every subject except for the bath size. Because of limited space, a 500ml container couldn’t
fit inside the thermal insulation chamber, therefore, the container was reduced to 300ml.
Although the bath size was smaller, the performance remains unaffected.
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In practice, the water bath could be utilized not only in thawing process but also in any
experiment that require a specific temperature to occur. It can even be used in heating
proteins, drugs, or materials that have unique melting point. Another advantage is that the
device was based on thermoelectric, which require very little power to operate, and the
compactness makes it easier to fit in any space of the laboratory. The control procedure of
the device was simplified so the user can interact with the device quickly and easily with
only spin-and-click actions.
5.2.Shortcomings
However, the water bath also has its limitations. The first thing to mention is that the
control system cannot directly change from cooling mode to heating mode and vice versa.
The PID algorithm run on accumulated errors, but cooling and heating process have
different sets of tuning. Therefore, when the user switches from one mode to the other
while keeping the same error, it would cause the values from different tuning values to add
up and affect the accuracy of the controller.
Another thing to add is the cooling efficiency of the water bath is dependent on the
performance of the heatsink, hence it is heavily affected by ambient temperature.
Therefore, the device is best suited to work at an AC-controlled room temperature, and it
is advised to use more specialized cooling method in more extreme environment.
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5.3.Implementations
For further development, the controlling program of the water bath can be upgraded.
For example, the algorithm can be improved to be able to change between different modes
directly or to adjust the rising time of the system at will. The temperature readings can be
recorded real time so the user can track the performance of the device and give appropriate
calibration. The interaction with the water bath can be made wireless so the user can access
the device anywhere while still be able to follow the status of it, further information on this
can be referred to [24].
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CHAPTER VI
CONCLUSION
To sums up, the thermostatic water bath can offer a variety of applications in the
laboratory regarding thawing or heating processes. It can aid in different procedures and
significantly reduced the time required for preparing materials or samples. Every
component was designed to connect sturdily with very little to no excess parts, reducing
the size of the system as much as possible. Although there are some limitations which can
be improved, the thermostatic water bath is a reliable device to be utilized in the laboratory.
It also has many rooms for improvement in the future that can be upgraded to provide more
utilities and functions for the users. Additionally, thermoelectric technology is still an
innovative method for temperature control, and it is expected to be developed further to
give even better performance in the future.
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R. L. B. T.-T. R. O. V. M. (Second E. Wernli, Eds. Oxford: Butterworth-Heinemann,
2014, pp. 141–161.
[23]
L. D. Pyeatt and W. Ughetta, “Chapter 11 - Devices,” L. D. Pyeatt and W. B. T.-A.
R. M. 64-B. A. L. Ughetta, Eds. Newnes, 2020, pp. 405–444.
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N. Hasim, M. F. Basar, and M. S. Aras, “Design and development of a water bath
control system: A virtual laboratory environment,” in 2011 IEEE Student
Conference on Research and Development, 2011, pp. 403–408.
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Biomedical Engineering Department
APPENDIX
SOFTWARE CODE SCRIPT
#include <DS18B20.h>
#include <PID_v1.h>
#include <SPI.h>
#include <OneWire.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
//define sensor pin
DS18B20 ds(13);
//define BTS7960 pins
int R_PWM = 6; //cooling pin
int L_PWM = 11; //heating pin
//define rotary pin
int clk = 8;
int dt = 9;
int sw = 10;
unsigned long inittime, lasttime;
//menu value
int last;
int curr;
int PID_value_fixed = 0;
int menu_act = 0;
int button_pressed = 0;
unsigned long lastBtnPress = 0;
String mode;
String modeoff = String("Off");
String modecooling = String("Cooling");
String modeheating = String("Heating");
//Set initial PID controller variables
double kp, ki, kd; //PID specifications
double realtemp=0, pwm=0; //PID input and outputs
double settemp=22;
float diff;
//initial tuning parameters
PID myPID(&realtemp, &pwm, &settemp, kp, ki, kd, DIRECT);
void(*controlTEC)(); //Pointer control TEC
void setup() {
//Interrupt settings
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Biomedical Engineering Department
PCICR |= (1 << PCIE0); //Enable PCMSK0 scan
PCMSK0 |= (1 << PCINT0); //Set pin D8 as state change interrupt
PCMSK0 |= (1 << PCINT1); //Set pin D9 as state change interrupt
PCMSK0 |= (1 << PCINT2); //Set pin D10 as state change interrupt
pinMode(clk, INPUT);
pinMode(dt, INPUT);
pinMode(sw, INPUT);
last = digitalRead(clk);
//PID settings
pinMode(R_PWM, OUTPUT);
pinMode(L_PWM, OUTPUT);
myPID.SetOutputLimits(-255,255);
myPID.SetMode(AUTOMATIC);
mode = modeoff;
controlTEC = &state; //Initial state
lcd.init();
lcd.backlight();
Serial.begin(115200);
}
void loop() {
realtemp = readThermocouple(); //Write thermocouple data as input
diff = realtemp - settemp;
//State control
controlTEC();
Serial.println(realtemp);
Serial.println(mode);
//Main menu
inittime = millis();
if ((inittime - lasttime) > 200) { //LED refresh rate
if (menu_act == 0) {
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Set temperature");
lcd.setCursor(0,1);
lcd.print(settemp);
}
if (menu_act == 1) {
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Mode");
lcd.setCursor(0,1);
lcd.print(mode);
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International University
Biomedical Engineering Department
}
if (menu_act == 2) {
lcd.clear();
lcd.setCursor(0,0);
lcd.print("T:");
lcd.setCursor(2,0);
lcd.print(realtemp,1);
lcd.setCursor(9,0);
lcd.print("S:");
lcd.setCursor(11,0);
lcd.print(settemp,1);
lcd.setCursor(0,1);
lcd.print("PWM:");
lcd.setCursor(4,1);
lcd.print(pwm,1);
}
lasttime = inittime;
}
}
//Thermocouple reading
double readThermocouple() {
float v;
while (ds.selectNext()){
v = ds.getTempC();
}
return v;
}
//Interrupt vector
ISR(PCINT0_vect) {
if (menu_act == 1) {
curr = digitalRead(clk);
if (curr != last && curr
if (digitalRead(dt) !=
mode = modecooling;
} else {
mode = modeheating;
}
}
last = curr;
delay(1);
}
if (menu_act == 0) {
curr = digitalRead(clk);
if (curr != last && curr
if (digitalRead(dt) !=
settemp += 0.5;
} else {
== 1) {
curr) {
== 1) {
curr) {
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International University
Biomedical Engineering Department
settemp -= 0.5;
}
}
last = curr;
delay(1);
}
//button menu
if (digitalRead(sw) == LOW) {
if (millis() - lastBtnPress > 50) {
button_pressed = 1;
}
lastBtnPress = millis();
} else if (button_pressed == 1) {
if (menu_act == 2) {
menu_act = 0;
PID_value_fixed = 1;
button_pressed = 0;
delay(1000);
}
if (menu_act == 1) {
menu_act += 1;
button_pressed = 0;
delay(1000);
}
if (menu_act == 0 && PID_value_fixed != 1) {
menu_act += 1;
button_pressed = 0;
delay(1000);
}
PID_value_fixed = 0;
}
}
void state(){ //Change state of the TEC module
if (mode == modecooling) {
controlTEC = &cooling;
} else if (mode == modeheating) {
controlTEC = &heating;
} else if (mode == modeoff) {
controlTEC = &off;
}
}
//PID control value
void cooling(){
kp = 200;
ki = 2.4;
kd = 0;
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Biomedical Engineering Department
myPID.SetTunings(kp, ki, kd);
myPID.SetOutputLimits(-255,0);
myPID.Compute();
analogWrite(R_PWM, abs(pwm));
analogWrite(L_PWM, 0);
if (true)
controlTEC = &state;
}
void heating(){
kp = 35;
ki = 1.3;
kd = 0;
myPID.SetTunings(kp, ki, kd);
myPID.SetOutputLimits(0,255);
myPID.Compute();
analogWrite(R_PWM, 0);
analogWrite(L_PWM, abs(pwm));
if (true)
controlTEC = &state;
}
void off(){
analogWrite(R_PWM, 0);
analogWrite(L_PWM, 0);
if (true)
controlTEC = &state;
}
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