Temperature Controlled System

PROJECT REPORT Mi

Temperature Controlled System Mini Project Kunal Ray Manish Kumar

2009

DEPARTMENT OF INSTRUMENTATION

Mini Project Report – Temperature Controlled System

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 2

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System

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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System

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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System

PART I

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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System

PART II

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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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 12

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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 13

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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 14

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System A LM 35 temperature sensor provides extremely dependable measurement of temperature, which can be observed using a multimeter 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System

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 17

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System  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 doublethrow (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. 19

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Mini Project Report – Temperature Controlled System

PART III

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Mini Project Report – Temperature Controlled System 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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Mini Project Report – Temperature Controlled System 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. 23

Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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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Kunal Ray, Manish Kumar

Mini Project Report – Temperature Controlled System 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.

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Kunal Ray, Manish Kumar