08-01-2013, 02:36 PM
DESIGN AND CONSTURCTION OF DIGITAL AUTOMATIC TEMPERATURE CONTROLLER
1DESIGN AND CONSTURCTION.docx (Size: 16.42 KB / Downloads: 27)
INTRODUCTION
An automatic Temperature Controller is a devise used to hold a desired temperature at a specified value. We are designing this automatic thermal control circuit which can be used in applications where automatic temperature control is needed.
The simplest example of a temperature controller is a common thermostat found in homes. For instance, a hot water heater uses a thermostat to control the temperature of the water and maintain it at a certain commanded temperature. The circuit switches an immature relay ON or OFF according to the temperature sensor LM35D7. When the LM35D7 detects a temperature higher than the preset level, the relay is actuated. When the temperature falls below the preset temperature, relay is de-energized. Temperature Controllers are also used in ovens. When a temperature is set for an oven, a controller circuit monitors the actual temperature inside the oven. If it falls below the set temperature (being indicated by the digital display unit), it sends a signal to activate the heater to raise the temperature back to the set point or reference point. The circuit can be powered by any AC or DC 12V supply or battery (100mA minimum).
AIMS AND OBJECTIVES
The main aim and objective of this proposal is to seek for the approval of the design and construction of digital automatic temperature Controller which has many benefits and applications in various industries as will be discussed.
WORKING PRINCIPLES
All Controllers from the basic to the most complex, work almost the same way. Controllers control or hold some variable or parameter of a set value.
The heart of the circuit is the LM35D7 temperature sensor which is the factory – calibrated in the Celsius (or centigrade) scale with a linear degree – volt conversion function. The output voltage (at pin 2 of LM35D7) changes linearly with temperature from OV (OoC) to 100mV(100oC). This greatly simplified the circuit design as we only need to provide a precision
voltage reference (TL431) and an accurate comparator (A1 or LM358) in order to construct a complete automatic thermal – controlled switch, the preset (VRI) and resistor (RI) from a variable voltage divider which sets a reference voltage (Vref) from OV-1.62V. The Op – Amp (A2) buffers the reference voltage so as to avoid loading the divider network (VRI and RI). The comparator (AI) compares the reference voltage (Vref) set by VRI with the output voltage of LM35D7 and decides whether to energize or de-energize the relay (LED ON or OFF respectively).
CONCLUSION
In reference to the above operation principle and benefits or applications of digital automatic temperature controller in various industries; packaging industry, heat treat/oven, plastic, health care, food and beverage industry which solved industrial temperature problems, the approval of the project will definitely appreciated by various industries mentioned.