25-04-2011, 04:55 PM
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ABSTRACT
Through our project we are showing the control of constant temperature according to the desired value (set point) in a closed loop using PID controller system. For this, we are using a microcontroller, a temperature sensor for sensing the temperature of the closed loops. By using the microcontroller we compare the desired value with current value and it is displayed in the LCD. Also to provide the constant temperature, Fan or Heater is turned On or Off according with the variations of current temperature in oC from desired setpoint.
INTRODUCTION
The objective of our project “TEMPERATURE PID CONTROLLLER” is maintaining the constant temperature in a particular area using PID controller.
Whatever the process or the parameter (temp, flow, speed, ..) the principles of control are similar. Input and output signals are specified in this project is digital. Control of a process is achieved by means of a closed loop circuit. This project is prepared in order to control the temperature of a furnace in the best and easiest possible way.
The control system is that means by which any quantity of interest in a machine, mechanism or other equipment is maintained or altered in accordance with a desired manner. Here we have used the closed loop system; that is the feedback system. The feedback signal is derived from the output of the system. This signal gives the capability to act as self correcting mechanism. The beneficial effects of the feedback in the system with high loop gain. The controlled variable accurately follows the desired value and also feedback in a control system greatly improves the speed of its response.
One of the primary purposes of using feedback in control system is to reduce the sensitivity of the system to parameter variations.
The project deals with a simple aspect of giving information about the controlling of temperature in a furnace. In this project we are developing a system, which can control temperature of a furnace automatically. The system is be capable of taking decisions accordingly of overheating of blast furnace and cooling of a furnace.
This project is done by using microcontroller (PIC 16F873A) which was developed by microchip company with several features than processors with cheap cost. A temperature LM 35 is used in sensing the temperature and relays like heater or fan are used for adjusting the temperature with desired temperature value. The functions occurring are displayed on the liquid crystal display.
In this system, it can implement any applications about controlling or monitoring the temperature without any human effort.
BLOCK DIAGRAM DESCRIPTION
The block diagram for “temperature PID controller” circuit consist of
• IC LM 35
• PIC 16F873A
• POWER SUPPLY
• RELAY
• DISPLAY SECTION
A fixed three terminal voltage regulator has a regulated dc output voltage of 5v and provide it to IC LM 35, PIC 16f873A, micro keys, relays and display section
Temperature sensing section consists of an IC LM 35 which acts as a transducer. It senses the temperature and converts it into voltage as a scale of 1oC into 10mv.
At the heart of the circuit is microcontroller PIC 16F873A with many advantages and it is available in RISC architecture.
The output of the microcontroller is give to the relays and display section.
Relays we used here are Heater and Fan; they are used for adjusting the obtained temperature with the desired temperature value.
The display section, through the IC LM020L, that displays temperature. It is the main observable part of this whole system.
OVERALL CIRCUIT DIAGRAM
LIST OF COMPONENTS
• REGULATOR 7805
• PIC 16F873A
• LM35
• LCD DISPLAY – LM020L
• RELAYS (2)
• CRYSTAL – 4MHz
• MICROSWITCHES (4)
• DIODES – 1N4007 (4)
• CAPACITORS
C1 - 1000µF
C2 – 100µF
C3, C4 – 33pF
• RESISTORS
R1 – 10k (4)
R2, R3 – 1k
• TRANSFORMER
• TRANSISTORS – BC548 (2)
OVERALL CIRCUIT DIAGRAM WORKING
The circuit shows microcontroller based temperature PID controller using temperature sensor.
Microcontroller PIC 16F873A is the heart of the circuit. It is available in
RISC architecture. The PIC 16F873A is a mid-range 8-bit CPU optimized for Control
Applications. It has 35 instructions on chip flash program memory.
LM35 used as the temperature sensor. It sense the current temperature of a closed loop and converts into corresponding voltage as it is a transducer. It is connected to pin 2 (RA0/AN0) of microcontroller. The microcontroller circuit is connected with reset circuit and crystal oscillator circuit. Crystal oscillator is the one used to generate the pulses to the microcontroller and it is also called as the heart of microcontroller. Here we have used 4 MHz crystal which generates pulses. It offers the highest precision (exactness/accuracy) and stability.
Even the microcontroller has an internal RC oscillator with a maximum frequency of 4 MHz, noise affect it easily. Because of increasing of aging of oscillator, resonant frequency varies and cannot get the fixed frequency. So we use crystal oscillator externally for accuracy.
To set up the desired temperature value, we use the micro keys such as SET, UP, DOWN. And also the tolerance value is set in the firmware using embedded C language.
According to the comparison of desired temperature (here we say as ‘Set point’) with the current temperature, the relay - Heater or Fan is worked.
Case I:
If the current temperature is greater than desired temperature (including tolerance) then turn off the heater and turn on the fan.
Case II:
If the current temperature is less than the desired temperature (including tolerance), then turn on the heater and turn off the fan.
Case III:
Else turn off both heater and fan.
The relays such as heater connected to pin 25 (RB4) and fan is connected to pin 26 (RB5).
The processing of controller will display in the LCD. The current temperature as ‘CT’ and the set point as ‘SP’can be observed on the first line of LCD. And also, the present conditions of the relays are displayed on the second line of the LCD.
