08-16-2017, 09:31 PM
Abstract
Temperature controllers are used in most of the manufacturing industries. The industries like textile mill, pharmaceutical industry, oil refinery etc. all requires temperature controller. The temperature controllers are used to maintain constant temperature of process or plant or any material. In such temperature controller system there is one reference temperature called set point or set temperature that is the desired temperature that must be maintained. This reference temperature is set by external means. Also it can be always adjustable according to requirements. Once this temperature is set the system tries to maintain it by sensing the current temperature and controlling it using heater, cooler or compressor etc.
It senses current temperature, compares it with reference temperature and generates error signal. Then based on this error signal it controls heating element (or cooling element). If set temperature is more then error signal is negative and vice versa.
So here I have given one such temperature control system that senses current temperature using temperature sensor. It compares it with the set temperature that is set by external reference. And it gives indication of error signal as positive or negative.
If error is positive that means current temperature is more than set temperature that has to be reduced
If error is negative that means current temperature is less than set temperature and it is required to increase it
Introduction
This practical temperature controller controls the temperature of any device according to its requirement for any industrial application. It also displays the temperature on an LCD displays in the range of 55 C to +125 C. At the heart of the circuit is the microcontroller from 8051 family which controls all its functions.
An IC DS1621 is used as temperature sensor. The DS1621 Digital Thermometer and Thermostat provides 9-bit temperature readings, which indicate the control of temperature of the device. User-defined temperature settings are stored in a nonvolatile memory EEPROM through 8051 series microcontroller.
Maximum and minimum temperature settings are entered to the MC through a set of switches which are stored in the EEPROM -24C02.Maximum and minimum setting are meant for allowing any hysteresis necessary. Set button is used first and then the temperature setting by INC and then the enter button.
Similarly for the DEC button. A relay is driven from the MC through a transistor driver. The contact of the relay is used for the load, shown as a lamp in the circuit. For high power heater load a contactor may be used, the coil of which is operated by the relay contacts in place of the lamp as shown.
Standard power supply of 12 volt DC and 5 volt through a regulator are made from a step down transformer along with a bridge rectifier and filter capacitor.