Sharp R-1880LS Service Manual page 13

The time of supplementary cooking is determined by experiment
with each food category and inputted into the LSI.
An example of how sensor works:
1. Potatoes at room temperature. Vapor is emitted very slowly.
. Heat potatoes. Moisture and humidity is emitted rapidly. You
can smell the aroma as it cooks.
AH SENSOR
3. Sensor detects moisture and humidity and calculates cooking
time and variable power.
Cooking Sequence.
1. Touch SENSOR COOK, SENSOR REHEAT or POPCORN
pad. When Sensor Cook is touched, to choose menu the
number pad should be touched.
NOTE: The oven should not be operated on SENSOR COOK,
SENSOR REHEAT or POPCORN immediately after
plugging in the unit. Wait five minutes before cooking on
SENSOR COOK, SENSOR REHEAT or POPCORN.
. The coil of shut-off relays (RY1, RY4 and RY5) are energized,
the oven lamp, turntable motor and cooling fan motor are
turned on, but the power transformer is not turned on.
3. After about 3 seconds, the cook relay (RY) is energized.
The power transformer is turned on, microwave energy is
produced and first stage is started.
The 3 seconds is the cooling time required to remove any
vapor from the oven cavity and sensor.
NOTE: During this first stage, do not open the door or touch
STOP/CLEAR pad.
4. When the sensor detects the vapor emitted from the food, the
display switches over to the remaining cooking time and the
timer counts down to zero.
At this time, the door may be opened to stir food, turn it or
season, etc.
5. When the timer reaches zero, an audible signal sounds. The
shut-off relay and cook relay are de-energized and the power
transformer, oven lamp, etc. are turned off.
6. Opening the door or touching the STOP/CLEAR pad, the time
of day will reappear on the display and the oven will revert to
an OFF condition.
BROIL, ROAST, BAKE
BROIL, ROAST and BAKE will automatically compute the oven
temperature, microwave power and cooking time for broiling,
roasting and baking. Set the desired program by touching one of
the BROIL, ROAST or BAKE pad, and number pad. Enter the
weight by touching the Number pads. When the START pad is
touched, the following operations occur:
1. The COOK indicator will light and the CONV or MIX indicator
will light.
. The cooking time will appear on the display and start counting
down to zero. The cooking time is adjusted automatically
according to the weight of the food.
3. The shut-off relays (RY1, RY4, RY5 and RY7) are energized,
turning on the oven lamp, turntable motor, cooling fan motor
and convection motor. The power supply voltage is applied
to the heating element.
4. Now, the oven is in the convection cooking mode or A utomatic
Mix Cooking condition.
5. When the oven temperature has reached the programmed
convection temperature, the oven goes into the programmed
cooking mode.
6. At the end of the cooking cycle, the damper is returned to the
open position and the oven will go to the off condition. The
cooling fan will remain on until the oven has cooled.
TIMED DEFROST COOKING
The DEFROST key is a special function key to defrost meats and
poultry faster and better. DEFROST automatically defrosts roast
beef, etc.. When the DEFROST is selected and the food weight is
entered by using the DEFROST pad, the oven will cook according
to the special cooking sequence.
FIRE SENSING FEATURE (MICROWAVE MODE)
This model incorporates a sensing feature which will stop the
oven's operation if there is a fire in the oven cavity during mi-
crowave cooking.
This is accomplished by the LSI repeatedly measuring the voltage
across the temperature measurement circuit (thermistor) during it's
3-seconds time base comparing the obtained voltage measure-
ments. If the most recent voltage measured is 100mV 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
and fan motor. The LSI also stops counting down and closes the
damper plate so that no fresh air will enter the oven cavity. Please
refer to the following section for a more detailed description.
Operation
The following operation will start 4 minutes after the start pad is
touched. Please refer to the timing diagrams below.
1. The thermistor operates within a 3-seconds time base and
it is energized for three (3) seconds and off for 9 seconds.
Two () seconds after the thermistor is energized, the voltage
across the temperature measurement circuit is sampled by the
LSI and twenty one (1) seconds after the thermistor is cut off
the LSI turns on the convection motor for six (6) seconds.
. 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 ) is greater than 100mV the
LSI makes the judgment that there is a fire in the oven cavity
and will switch off the relays to the power transformer and
fan motor. The LSI also stops counting down and closes the
damper door so that no fresh air will enter the oven cavity.
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.
IMPORTANT:
During sensor cooking operation, the fire sensing op-
eration sequence will not begin until the AH sensor has
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R-1880LS/LST