Temperature Controlled System

Mi

PROJECT REPORT

2009

Temperature Controlled

System Mini Project

Kunal Ray

Manish Kumar

D E P A R T M E N T O F I N S T R U M E N T A T I O N

Mini Project Report – Temperature Controlled System

2

Kunal Ray, Manish Kumar

DESIGN OF TEMPERATURE CONTROLLED

SYSTEM

A Mini Project Report

Submitted To the Faculty Of The

Department of Instrumentation

Cochin University of Science And Technology

Towards partial fulfillment of the requirements for the Degree of B.Tech.

In Instrumentation Engineering

By

Kunal Ray

&

Manish Kumar

Approved By:

Mrs. Suniya V. S.

&

Mr. Anwar Sadath


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Acknowledgement

We would like to express our heart-felt gratitude to our project guides Mrs. Suniya

V. S. and Mr. Anwar Sadath for their unflinching support and guidance towards

the completion of this project. It is due to their kind support and timely advice that

this project has been able to see the light of the day.

Furthermore, our sincere thanks go to our Head of Department Dr. K. N.

Madhusodanan, who not only very kindly allowed us to make use of all the

excellent facilities in the Department, be it the workshop or the various

laboratories, but also channelized our resources in the right direction through

periodic mentoring.

We would also like to express our thanks to our Laboratory In-Charge Mr. Gopi

Menon for his constant backing and exceptional guidance.

Lastly, we would like to express our heartfelt gratitude to all our batchmates from

the class of 2010, who not only provided moral support but also helped us in every

way possible such that the project was completed in time and in a smooth manner.

Kunal Ray

Manish Kumar


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TABLE OF CONTENTS

Introduction……...………………………………………………………………05

Part I – Physical Arrangement…...…………………………………………….06

Part II – Circuit Requirements………………………………………………...11

Part III – Working………………………………………………………………21

Conclusion………………………………………………………………………25


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Introduction: Temperature is a physical property of a system that underlies the

common notions of hot and cold; something that feels hotter generally has the

higher temperature. Temperature is one of the principal parameters

of thermodynamics. If no net heat flow occurs between two objects, the objects

have the same temperature; otherwise heat flows from the hotter object to the

colder object. This is the content of the zeroth law of thermodynamics.

Temperature control finds varied uses in our everyday lives. Be it common room

coolers, air-conditioners or large industrial devices like boilers; the ability to

control temperature has not only improved our everyday lifestyle but has also

aided in almost all industrial processes. In short, the capability of humans of

controlling the physical parameters around them such as temperature have been

instrumental in their all round growth.

In this project, a temperature controller has been introduced which works in a

controlled environment. It is basically an ON-OFF controller which works

according to the value of the temperature. In other words, when the temperature

exceeds or is less than the set point value of temperature, corrective action is taken

to rectify it.

The project report given here is divided into three parts, where the first two parts

discuss the physical arrangements and the circuit requirements of the project giving

a detailed description of all the components used; and the third part gives a

thorough explanation of the working of the apparatus and how is it able to qualify

as a temperature controlled system.


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PART I


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Physical Arrangement:

A block diagram explaining the operation and physical structure of the project is

shown below:

The components used in order to create the physical controlled environment for the

project are as follows:

12V/0.25A DC Brushless Fans (2 nos.)

Nichrome wire wounded heater – 500Ω (1nos.)

LM35 Temperature sensor (1 nos.)

Tin Container (1 nos.)

Glass lid.


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A detailed description of the components has been explained below:

12V DC Brushless Fans: The fans used for this project are of the DC Brushless

type. The cross-sectional diagram and the specifications are provided below –


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The specifications of the fan, as obtained from the manufacturer are as follows:

1. Voltage – 12

2. Current – 0.25

3. Power – 3.0

4. RPM – 3010

5. Air Flow (CFM) – 38.6

6. Pressure (inches) – 0.160

7. Noise (dB/A) – 34.4

8. Weight (gm) – 86


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Nickel-Chromium Strip Heater: A nickel-chromium (nichrome) heater of room

temperature resistance 500Ω has been used. A cross-sectional for the same is

shown –

When connected to a 230V AC power supply with a 5A current supply, the heater

is capable of reaching temperatures up to 120ºC. It is ideal for the project given its

ability to attain high temperatures in relatively low time intervals.


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PART II


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Circuit Requirements: The circuit employs the following components. A brief

description of every such component is given along with their specifications to

facilitate understanding.

CA3130 Comparator (1nos.): A schematic of the CA3130

comparator is shown below.

Pin Out Diagram

The CA3130 series circuits operate at supply voltages ranging from

5V to 16V (±2.5V to ±8V). They can be phase compensated with a

single external capacitor, and have terminals for adjustment of offset

voltage for applications requiring offset-null capability. Terminals

provisions are also made to permit strobing of the output stage.

Absolute Maximum Ratings:

1. DC Supply Voltage (Between V+ And V- Terminals) . . . . .16V

2. Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . .8V

3. DC Input Voltage . . . . . . . . . . . . . . . . . .(V+ +8V) to (V- -0.5V)

4. Input-Terminal Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1mA

5. Output Short-Circuit Duration (Note 1) . . . . . . . . . . . Indefinite

6. Operating Conditions Temperature Range . . . . . -50ºC to 125ºC


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A schematic diagram for the CA3130/3130A comparator is given below:

Explanation:

Input Stage: The circuit of the CA3130 is shown in the schematic diagram.

It consists of a differential-input stage using PMOS field-effect transistors

(Q6, Q7) working into a mirror-pair of bipolar transistors (Q9, Q10)

functioning as load resistors together with resistors R3 through R6. The

mirror-pair transistors also function as a differential-to single-ended


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converter to provide base drive to the second stage bipolar transistor (Q11).

Offset nulling, when desired, can be effected by connecting a 100,000Ω

potentiometer across Terminals 1 and 5 and the potentiometer slider arm to

Terminal 4.

Cascade-connected PMOS transistors Q2, Q4 are the constant-current source

for the input stage. The biasing circuit for the constant-current source is

subsequently described. The small diodes D5 through D8 provide gate-oxide

protection against high-voltage transients, including static electricity during

handling for Q6 and Q7.

Output Stage: The output stage consists of a drain-loaded inverting

amplifier using CMOS transistors operating in the Class A mode. When

operating into very high resistance loads, the output can be swung within

milli-volts of either supply rail. Because the output stage is a drain-loaded

amplifier, its gain is dependent upon the load impedance. The transfer

characteristics of the output stage for a load returned to the negative supply

rail are shown in the figure. Typical op amp loads are readily driven by the

output stage. Because large signal excursions are non-linear, requiring

feedback for good waveform reproduction, transient delays may be

encountered. As a voltage follower, the amplifier can achieve 0.01%

accuracy levels, including the negative supply rail.

LM 35 Temperature Sensor (1nos.): The LM35 series are precision

integrated-circuit temperature sensors, whose output voltage is

linearly proportional to the Celsius (Centigrade) temperature. The

LM35 thus has an advantage over linear temperature sensors

calibrated in ° Kelvin, as the user is not required to subtract a large


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constant voltage from its output to obtain convenient Centigrade

scaling. The LM35 does not require any external calibration or

trimming to provide typical accuracies of ±1⁄4°C at room temperature

and ±3⁄4°C over a full −55 to +150°C temperature range. Low cost is

assured by trimming and calibration at the wafer level. The LM35’s

low output impedance, linear output, and precise inherent calibration

make interfacing to readout or control circuitry especially easy. It can

be used with single power supplies, or with plus and minus supplies.

As it draws only 60 μA from its supply, it has very low self-heating,

less than 0.1°C in still air. The LM35 is rated to operate over a −55° to

+150°C temperature range, while the LM35C is rated for a −40° to

+110°C range (−10° with improved accuracy).

Connection Schematic – LM35.


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A LM 35 temperature sensor provides extremely dependable

measurement of temperature, which can be observed using a multi-

meter with the help of basic calibration.

IC7806-3pin voltage regulators (1nos.): These voltage regulators are

monolithic integrated circuits designed as fixed–voltage regulators for

a wide variety of applications including local, on–card regulation.

These regulators employ internal current limiting, thermal shutdown,

and safe–area compensation. With adequate heat sinking they can

deliver output currents in excess of 1.0 A. Although designed

primarily as a fixed voltage regulator, these devices can be used with

external components to obtain adjustable voltages and currents. The

pin diagram for the IC is shown as follows:

The standard method for connecting a 7806 voltage regulator is shown

below:


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The IC7806 used in this project provides a 6V output voltage, which

is used to drive all the different components like the comparator,

temperature sensor and the TIP122 which is explained below. Hence,

it provides a regulated output voltage maintained at 6V.

TIP122 Darlington (1nos.): A TIP122 is an NPN epitaxial

Darlington transistor. In electronics the Darlington transistor (often

called a Darlington pair) is a compound structure consisting of two

bipolar transistors (either integrated or separated devices) connected


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in such a way that the current amplified by the first transistor is

amplified further by the second one. This configuration gives a much

higher current gain (written β, hfe, or hFE) than each transistor taken

separately and, in the case of integrated devices, can take less space

than two individual transistors because they can use

a shared collector. Integrated Darlington pairs come packaged in

transistor-like packages. A TIP122 along with its equivalent circuit

diagram is shown below:

A Darlington pair behaves like a single transistor with a high current

gain (approximately the product of the gains of the two transistors). In

fact, integrated devices have three leads (B, C and E), broadly

equivalent to those of a standard transistor.

A general relation between the compound current gain and the

individual gains is given by:

If β1 and β2 are high enough (hundreds), this relation can be

approximated with:


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6V Relay (1nos.): A relay is an electrically operated switch. Electric

current through the coil of the relay creates a magnetic field which

attracts a lever and changes the switch contacts. The coil current can

be on or off so relays have two switch positions and they are double-

throw (changeover) switches. A photograph of the relay used in the

project is given below –

A simple electromagnetic relay, such as the one taken from a

car in the first picture, is an adaptation of an electromagnet. It consists

of a coil of wire surrounding a soft iron core, an iron yoke, which

provides a low reluctance path for magnetic flux, a movable

iron armature and a set, or sets, of contacts; two in the relay pictured.

The armature is hinged to the yoke and mechanically linked to a

moving contact or contacts. It is held in place by a spring so that when

the relay is de-energized there is an air gap in the magnetic circuit. In

this condition, one of the two sets of contacts in the relay pictured is

closed, and the other set is open.


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When an electric current is passed through the coil, the

resulting magnetic field attracts the armature and the consequent

movement of the movable contact or contacts either makes or breaks a

connection with a fixed contact. If the set of contacts was closed when

the relay was de-energized, then the movement opens the contacts and

breaks the connection, and vice versa if the contacts were open. When

the current to the coil is switched off, the armature is returned by a

force, approximately half as strong as the magnetic force, to its

relaxed position. A figure showing a typical relay operation is shown

below –


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PART III


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Working: The circuit diagram for the temperature controlled system using all the

above described components is shown below followed by an elaborate explanation.


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In the figure above,

R1 = 1.2KΩ

R2= 10KΩ

R3=12KΩ

R4=5.6KΩ

R5= 10KΩ Potentiometer

R6= 680Ω

And

C1 = 47µF

C2= 1µF

C3 = 0.1µF

The working of the temperature controlled system is relatively easy to understand.

In the project, the set point temperature is controlled by varying the potentiometer.

This is manifested as the voltage output (in mV) of the potentiometer. At the same

time, the output from the LM35 gives the ambient temperature in terms of mV.

The output of the LM35 is given to the pin no. 3 (non – inverting) of the

comparator. At the same time, the set point voltage is provided to the pin no. 2

(inverting) of the comparator. Initially, when the LM35 output is lower as

compared to the set point, the output as displayed by the pin 6 of the comparator

remains low. As soon as the LM35 output exceeds the set point value, the output

pin 6 of the comparator becomes high and this drives the Darlington pair TIP122

which in turn drives the relay.


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Simultaneously, the relay, in the normally closed position, is connected in such a

manner that the heating coil is connected to the mains i.e. 230V AC. Therefore, the

heater warms the surrounding air and the ambient temperature inside the container

increases. As soon as the ambient temperature becomes more than the set point

temperature, the comparator output through the Darlington pair drives the relay

into the normally open position which drives the 12V DC brushless fans. The two

fans, one acting as blower and the other as exhaust, work together to reduce the

ambient temperature, thereby bringing it below the set point value at which, the

heater once again gets switched on and the temperature starts increasing. This

process of ON – OFF control continues and the ambient temperature is controlled

and maintained as close to the set point value as physically possible.


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Conclusion: Temperature control is a process in which change of temperature of

a space (and objects collectively therewith in) is measured or otherwise detected,

and the passage of heat energy into or out of the space is adjusted to achieve a

desired average temperature.

In this project, a simple yet effective method to control the ambient temperature of

a closed space is discussed. This method can be further improved to deal with

bigger areas like rooms etc. Temperature control finds usage in our households and

industries. Whether we realize it or not, more often than not, almost all the

electronic and electrical devices that we use have some method or the other to

control temperature.

We hope that the method discussed here finds use in some industrial application

and justifies our endeavour.

Documents

Temperature Controlled System