Electronic temperature controller

Abstract

Thermostats are temperature-sensitive devices used to control equipment in response to the demands of the space in which they are located. Until presently thermostats were operated by a bimetal or "feeler" bulb filled with a liquid that expands and contracts in response to temperature changes. Today, electronic temperature controllers are replacing these methods. THE CONTROLLER The aim of this project is to control a given process temperature accurately and reliably. To accurately control a process temperature without extensive operator involvement, a temperature control system consists of a controller, which accepts a temperature sensor or transducer such as a thermistor, and compares the actual temperature to the desired control temperature or setpoint, and then provides an output to a control element. The controller is one part of the entire control system, and the whole system should be analysed in selecting the proper controller. The following items should be considered when selecting a controller :- (i) TYPE OF INPUT (temperature transducers) - Thermocouple - Resistance Temperature Detector CRTD) Thermistor - Semiconductor temperature sensor (ii) CONTROL ALGORITHM NEEDED - On/Off Controller - Proportional Controller - P.I .D. Controller (iii) TYPE OF OUTPUT CONTROL - Electromechanical Relay - Solid State Relay or Triac - DC Voltage Pulse - Analog Output. (iv) TYPE OF OUTPUT ELEMENT - Heater (central-heating) - cooler (air-conditioning) - Alarm - Limiter In choosing a Temperature Controller, the main considerations include the precision of control that is necessary, and how difficult the process is to control. For easiest tuning and lowest initial cost, the simplest controller which will produce the desired results should be selected.