A MICROWAVE-OVEN WITH VARIABLE CONTINUOUS POWER AND A FEEDBACK TEMPERATURE CONTROLLER

The power supply circuit of a domestic microwave oven was modified so that the field intensity in the cavity could be changed continuously. The oven was further fitted with a feedback temperature controller for controlling product temperatures during microwave heating by cycling the magnetron on and off. The temperature controller consists of a fib er optic temperature sensing system, a computer, an optocoupler, and a mechanical relay. White bread, moist sponges, and a 5-mL water load w ere used to test the performance of the oven. The temperature control capability was greatly influenced by the field intensity of the cavity and less influenced by the data acquisition rate. Experimental data i ndicated that it was possible to maintain the sample temperature withi n +/- 0.3-degrees-C at 60-degrees-C and within +/- 0.6-degrees-C at 80 -degrees-C when a proper power level was used.