fabrication of controlled temperature chamber

7/24/2019 fabrication of controlled temperature chamber

1/12

1

TABLE OF CONTENTS

Sr.no Name12

3

4

5

678

9

10

11

1. Objective2.

Components

3. Temperature controller

4. Why do we need temperature controller

4.1Explanation

4.2

Basic knowledge of model of controller4.3Block diagram & circuit diagram5. System design

5.1Mathematical model

6. Simulation and results

7. Conclusion


2/12

2

1.Objective:This experiment deals with regulating temperature of a closed chamber by controlling the fanand heater using microcontroller.

2. Components Required:

PIC16f876a-I/SP microcontroller

Temperature sensor

7 segments LCD

4 Switches Keypad

Heater (AC Bulb) Fan

Relay and relay driver

DC motor and motor driver

3.Temperature controller

Temperature controllers are devices used to accurately control process temperature without

extensive operator involvement. It is a control system which accepts data from temperature

sensors such as thermocouples or Resistance Temperature Detectors (RTD) and compares theactual temperature to the desired set-point temperature, to operate temperature controlling

elements like coolers or heaters.

4.Why do we need temperature controller

In recent advanced era the temperature measurement and its control has become an

integral part of any control system operating in a temperature sensitive environment e. g.

The temperature of food items can be controlled to minimize the bacterial growth without

affecting its nutrition value. For boilers, temperature is important for water and air preheat, fuel oil viscosity, and

steam superheat control.


3/12

3

The temperature control in cold stores reduces the contamination and degradation rate in

pharmaceutical, biochemical, beverage and food industries.

The temperature control in plant growth chambers is important for studying the effect of

hybridization, genetic engineering and plant growth regulators.

Due to the above mentioned reasons we have to go for this experiment.

4.1 Explanation

A PIC16F876A Microcontroller is used for carrying out all the required computations and

control. It has an in-built Analog to Digital converter. Hence an external ADC is not required forconverting the analog temperature input into digital value. In the following discussion we willbriefly discuss about the temperature sensor used, the microcontroller and the project in general.

An inexpensive temperature sensor (Thermistor) is used for sensing the ambient temperature.

The system will get the temperature from the sensor IC and will display the temperature on theLCD. This temperature is compared with the set point temperature declared by the user (also

displayed on the LCD) using NPN Transistor switch. We are implementing On/Off control for

controlling the temperature. The temperature must be within a certain range otherwise

continuous on/Off of the controlling elements (heater and fan) will cause damage to them. Weconsider the temperature range to be 3

oC compared to the set temperature. If the Room /Chamber

temperature goes beyond the upper limit then fan will be switched ON and if temperature goes

below the lower limit then heater will be switched ON.

4.2 BASIC KNOWLEDGE OF PIC16F876A

PIC16F876A is an 8-bit high performance microcontroller. It consumes less power. They have

features such as internal PWM channels, 10-bit A/D converters, UART/USART and much more,which makes them useful for a large number of applications and external hardware is reduced as

these are built-in.


4/12

4


5/12

5

Block diagram

3D view in pro. e

Main circuitTransformer

lamp

Exhaust fan

PIC16f876a

Microcontroller

Temp. Sensor

Switches

Relay

Motor driver

Relay driver

7 segment

LCD

DC motor with FAN

Heater


6/12

6

Schematic diagram


7/12

7

Circuit diagram

The circuit diagram of the system is shown in the fig.

5.System design

The operation of the circuit is based on a PI Controller implemented on a microcontroller and a

temperature sensor. The temperature sensor converts change in temperature to change in

electrical signal which is then compared by the PI controller control algorithm to activate the fan

for the cooling of the system. The microcontroller accepts inputs from a simple four-key keypad


8/12

8

which allow specification of the Set point temperature and it displays both set-point and

measured chamber temperatures using an LCD display. Finally, a pulse-width modulation

(PWM) output from the controller is used to drive a relay which switches the fan off and on.


9/12

9


10/12

10

5.1Mathematical model of the Controller

The PI controller was selected since it is probably the most extensively used method in industrialprocess control applications. A large number of references can be found which describe the

continuous and digital forms of this controller, its performance evaluation, implementation and

auto-tuning forms. The block diagram of the continuous PI controller is shown in figure 6 where,Kp is the proportional gain, Ti is the integral time constant, The transfer function of the standardPI algorithm is:

() () ()

It can be written as in the S-domain as following:

()[ ]()


11/12

11

6.Simulation and results:


12/12

12

7.Conclusion

In this project, the performances of control strategies with feedback for a microcontroller

based temperature control in a controlled temperature system have been investigated. Acomparative study of performance of PI based controllers is studied. The aim of the proposed

controller is to regulate the temperature of the system to a desired temperature in the shortest

possible time with no overshoot, short rise time, small peak time and short settling time.Mathematical model was efficiently used for the design of the temperature control system. Some

aspects of theoretical modeling were described.

fabrication of controlled temperature chamber

Documents