Specifications

Ver SG 9/200 44 Sharp Electronics Corporation
Another factor which will affect the temperature circuit is the line voltage. If the voltage
is decreased the wattage output of the heating element will also be decreased.
Fire Sensing Feature (Microwave Mode)
The model R-820BK/BW incorporates a sensing feature which will stop the oven’s
operation if there is a fire in the oven cavity during microwave cooking.
This is accomplished by the LSI repeatedly measuring the voltage across the temperature
measurement circuit (thermistor) during it’s 32-seconds time base comparing the
obtained voltage measurements. If the most recent voltage measured is 700mV greater
than the previous voltage measured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the power transformer, fan motor, oven lamp and turntable
motor. The LSI also stops counting down. Please refer to the following section for a
more detailed description.
Operation
Please refer to the timing diagrams below
1. The thermistor operates within a 32-seconds time base and it is energized for three (3)
seconds and off for 29 seconds. Two (2) seconds after the thermistor is energized, the
voltage across the temperature measurement circuit is sampled by the LSI and twenty one
(21) seconds after the thermistor is cut off the LSI turns on the cooling fan for six (6)
seconds.
2. The above procedure is repeated.. If the difference between the first voltage measured
(in step 1) and the voltage measured when the procedure is repeated (step 2) is greater
than 700mV the LSI makes the judgement that there is a fire in the oven cavity and will
switch off the relays to the power transformer, fan motor, oven lamp and turntable motor.
The LSI also stops counting down.
3. Once the fire sensor feature has shut the unit down, the programmed cooking cycle
may be resumed by pressing the “START” pad or the unit may be reset by pressing the
“CLEAR” pad.