This project is titled design and construction of a temperature control circuits. It is designed to control the temperature of the electric such as electric kettle, oven, incubator to a variable range (0°C -100°C) which must be set by the user or operator. And this can be achieved by the use of temperature sensor known as THERMISTOR. This thermistor is a temperature control device with a high or low resistance value which can go high or low when the temperature is increased or reduced depending on the type.
 
In this project, 100C is used as a set temperature. And this device is design in such a way that when the temperature of the liquid inside the kettle is reached, the heater of the device will automatically switched-off and will maintain the off stage until when the temperature the liquid is dropped 97°C, and then it will switch-ON again in other to maintain that 100°C. And this automatic feature is controlled by a high current relay.

TABLE OF CONTENT
Title Page
Approval Page
Dedication
Acknowledgement
Abstract
Table of Content

CHAPTER ONE
1.0      Introduction
1.1      objective of the project
1.2      significance of the project
1.3      application of the project
1.4      scope of the project
1.5 limitation of the project
1.6 project organisation

CHAPTER TWO
2.0      Theory of Major Components used
2.1      Theory of Resistors
2.2      Theory of Diodes
2.3      Theory of Capacitors
2.4      Theory of Transformers
2.5      Theory of Transistor
2.6      Theory of Integrated Circuit
2.7     Theory of Thermistor

CHAPTER THREE
3.0      Sectional Description of the System 
3.1      Comparator Section
3.2      Switching (relay) Section
3.3      Power supply
3.4     sensor
3.5    circuit operation

CHAPTER FOUR
4.0      Construction Procedure and Testing
4.1      Casing and Packaging
4.2      Assembling of Sections
4.3      Testing of System Operation     
4.4      Installation of the Completed System
4.5      Problem Encountered
4.6      Cost Analysis

CHAPTER FIVE
5.0      Conclusion
5.1      Recommendation
5.2      Bibliography

CHAPTER ONE
1.0                                                        INTRODUCTION

1.1                                         BACKGROUND OF THE PROJECT
A temperature control appliances such as household  electric kettle usually has a heating element which is mounted at the bottom of a water tank through a heat conducting base. A conventional temperature control system typically uses a bi-metal temperature sensor (also known as a thermostat) to sense the water temperature and the steam when the water is boiled, and then cut off the electric power if the water temperature reaches the bi-metal action temperature point or if sufficient amount of steam is detected. Some modern electric kettles use more precise electronic temperature sensors such as the NTC (Negative Temperature Coefficient) resistors (thermistors), which are capable of sensing the water temperature through a very wide range of points instead of just one point. In some cases, the control systems of the electric kettles are configured to take into account the temperature rising rate in addition to the water's absolute temperature value so that the control precision is greatly improved. However, the heating system of an electric kettle is a very complicated energy balancing system. The heat generated by the heating element may be decomposed into the following main components:

a) Energy for heating up the water in the water tank;
b) Energy stored in the heat conducting base;
c) Energy dissipated through the outer case of the water tank and related to the case material and the case mass; and
d) Energy dissipated by emission through the surface the outer case and related to the surface area and the color of the water tank's body.

All of the above factors will affect the water temperature during the heating up and warmth keeping cycle, which may increase the difficulty of precisely controlling the water temperature. For example, the energy stored in the heat conducting base may increase the water temperature by a certain amount after the power supply is cut off, which causes the water temperature to overshoot. The choice of the material of the outer case may affect the water temperature significantly because energy loss is very serious when the water temperature is high. All these factors and effects should be taken into consideration in the design of electric kettles.

The idea behind the design and construction of this system is to make available or alternative means providing safety and accuracy demand for electric oven using for household or industrial purpose. This goes a long way in helping to curb the problem frequently encountered as a result of fire outbreak, burning of food, and inaccuracy found in measuring and maintaining temperature. That notwithstanding it makes it possible to have other means of heating food without constant temperature monitoring until when the required temperature will be achieved thereby creating time for the operator to be engaged on other works while the system is in operation.

Moreover, rate of fire accident cause by heating appliances in this country is high. So there is every need that other means of safety should be made available for constant running of our electric equipments and gadgets and also to provide comfort to man. Hence, with the help of a Thermistor, which has come to solve the problem of fire accident and inaccuracy found in temperature measurement in Nigeria, a steady running and operation of our electric equipments and gadgets is guaranteed.

1.2                               OBJECTIVE OF THE PROJECT
The objective of this work is to design to design a temperature control device which can control a temperature range of 0°C -100°C automatically – without the help of the user.

1.3                                         SIGNIFICANCE OF THE PROJECT
Temperature controlled circuits typically uses a temperature sensor (also known as a thermistor) to sense the water temperature and the steam when the water is boiled, and then cut off the electric power if the water temperature reaches the action temperature point or if sufficient amount of steam is detected. The temperature sensors, NTC (Negative Temperature Coefficient) resistors (thermistor), which is capable of sensing the water temperature through a very wide range of points.

1.4                                          APPLICATION OF THE PROJECT
Outside the culinary world, temperature control electric kettles are used for a number of purposes.

• A furnace can be used either to provide heat to a building or used to melt substances such as glass or metal for further processing. A blast furnace is a particular type of furnace generally associated with metal smelting (particularly steel manufacture) using refined coke or similar hot-burning substance as a fuel, with air pumped in under pressure to increase the temperature of the fire.
• A kiln is a high-temperature temperature control electric kettles used in manufacturing to convert mineral feedstock (in the form of clay or calcium or aluminum rocks) into a glassier, more solid form. In the case of ceramic kilns, a shaped clay object is the final result, while cement kilns produce a substance called clinker that is crushed to make the final cement product.
• An autoclave is an kettle-like device with features similar to a pressure cooker that allows the heating of aqueous solutions to higher temperatures than water's boiling point in order to sterilize the contents of the autoclave.
• Industrial temperature control electric kettles  are similar to their culinary equivalents and are used for a number of different applications that do not require the high temperatures of a kiln or furnace.

1.5                                                 SCOPE OF THE PROJECT
Temperature controlled circuits include a heating element for heating water contained in the intelligent electric kettle, a sensor for sensing the temperature of the water, and a control unit being configured to collect data during the operation of the circuits. The control unit is also configured to execute a predetermined program and calculate a cut-off temperature based on the data and a predetermined target temperature. The control unit is further configured to turn off the electric power provided to the heating element when the temperature of the water sensed by the sensor is equal to or greater than the calculated cut-off temperature.

1.7                                           LIMITATION OF THE PROJECT

Though temperature controlled circuits is designed to boil liquid, but when the sensor is directly exposed to liquid (water) can damaged the sensor thereby causing the sensor to malfunctioning.

1.6                          PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Chapter one of this work is on the introduction to a temperature control circuit. In this chapter, the background, significance, objective limitation and problem of a temperature control circuit were discussed.
Chapter two is on literature review of a temperature control circuit. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.

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