Low-Cost Electric Range Control using a TRIAC
Created: Sep 03, 2014
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Nowadays, cooking appliances uses adjustable mechanical thermostat in order to vary the heat it uses. However, there are several disadvantages such as the calibration of mechanical thermostat in factories, poor simmer performance means that the control is not precise when the output is at low temperatures, poor in accuracy, and mechanical components loses its reliability over time. Thus, the usage of low-cost microcontroller will replace mechanical thermostat, which minimize the effect of the said disadvantages.The main component used in the circuit is the PIC10F204 Microchip microcontroller that offers solution to design flexibility and user friendly features.
Electric ranges create heat by applying the AC line voltage across a resistive heating element. An adjustable mechanical thermostat in series with the heating element has a rotary dial which sets the amount of current to the element. The mechanical thermostat shown has a complex set of metal tabs, spacers and contacts that work together to connect and disconnect power depending on the setting of the rotary dial. The following sequence of events describes the operation of a mechanical thermostat when the dial is turned halfway between OFF and full ON. First, contact is made between the two terminals of the switch; second, resistive materials in the switch cause parts of the switch to heat and expand; third, the expansive materials push the contact apart and the switch stops conducting current and lastly,the element then cools until contact is made again. Based on the position of the dial, the switch repeats this sequence more or less frequently. The switch allows infinite control, but without a clear reference. As a result, the switch is not very accurate. The switch is constantly subjected to thermal changes and arching occurs frequently across the contacts when the dial is not in an absolute position (OFF and full ON). These stresses affect the reliability of the switch.
This design which showed the use of PIC10F204 and TRIAC is very much useful in full AC switching, personal care appliances and security systems to low-power remote transmitter/receivers.