Electrolux E30MO75HPS - 1.5 cu. Ft. Drop-Down Door Microwave, Technical & Service Manual

Page: 21 / 52

Operation
2-9
(3) Detector Circuit of Absolute Humidity Sensor
Circuit:
This detector circuit is used to detect the output
voltage of the absolute humidity circuit to allow the
LSI to control sensor cooking of the unit. When the
unit is set in the sensor cooking mode, 16 seconds
clearing cycle occurs then the detector circuit starts
to function and the LSI observes the initial voltage
available at its AN6 terminal.
With this voltage given, the switches SW1 to SW5 in
the LSI are turned on in such a way as to change the
resistance values in parallel with R50-1. Changing
the resistance values results in that there is the same
potential at both F-3 terminal of the absolute
humidity sensor and AN7 terminal of the LSI. The
voltage of AN6 terminal will indicate about -2.5V.
This initial balancing is set up about 16 seconds after
the unit is put in the Sensor Cooking mode.
As the sensor cooking proceeds, the food is heated
to generate moisture by which the resistance
balance of the bridge circuit is deviated to increase
the voltage available at AN6 terminal of the LSI.
Then the LSI observes that voltage at AN6 terminal
and compares it with its initial value, and when the
comparison rate reaches the preset value (fixed for
each menu to be cooked), the LSI causes the unit to
stop sensor cooking; thereafter, the unit goes in the
next operation automatically.
When the LSI starts to detect the initial voltage at
AN6 terminal 16 seconds after the unit has been put
in the Sensor Cooking mode, if it is not possible to
balance, of the bridge circuit due to disconnection of
the absolute humidity sensor, ERROR will appear on
the display and the cooking is stopped.
1) Humidity sensor circuit:
SW2
SW1
SW3
SW4
SW5
P30
P31
P32
P33
P34
LSI
(IC1)
AN7
AN6
620k
300k
150k
75k
37.4k
4
64
5 63
6
7
8
62
61
60
3
5
2
6
47k
47k
10k
0.01µF
0.015µF
0.01µF
360k
+
-
1 12
VA : -15V
VA : -15V
R51
9
S
F-2
10
1.8k
F-1
F-3
C
11
3.57k
3.32k
VC : -5V
0.1 µF
C. Thermistor in
closed vesssl
S. Thermistor in
open vessel
IC2(IZA495DR)
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system
where food is not directly heated by the heating element,
but is heated by forced circulation of the hot air produced
by the heating element. The air heated by the heating
element is circulated through the convection passage
provided on the outer casing of theoven cavity by means
of the convection fan which is driven by the convection
motor. It then enters the inside of the oven through the
vent holes provided on the left side of the oven. Next,
the hot air heats the food on the turntable and leaves the
oven cavity through the vent in the center of the oven
cavity left side wall.
Without leaving the oven, this hot air is reheated by the
heating element, passes through the convection passage
and enters the inside of the oven cavity again, in a
continuing cycle.
In this way, the hot air circulates inside the oven cavity to
raise its temperature and, at the same time, comes into
contact with the food being cooked.
When the temperature inside the oven cavity reaches
the selected temperature, the heating element is
de-energized. When the temperature inside the oven
cavity drops below the selected temperature, the heating
element is energized again. In this way, the inside of the
oven cavity is maintained at approximately the selected
temperature. When the convection time reaches 0, the
heating element is de-energized and the convection fan
stops operating and the oven shuts off.
DAMPER OPEN-CLOSE MECHANISM
Usually, the damper is in the open position except during
convection cooking. Damper position is set automatically
by damper motor, damper switch, motor cam and damper
shaft. These components are operated by a signal that
judges if microwave cooking or convection cooking
operation is selected by the control unit.
Microwave Cooking:
Damper is in the open position, because a portion of
cooling air is channelled through the cavity to remove
steam and vapors given off from the heating foods.
It is then exhausted at the top of the oven cavity into
a
c ondensation compartment.
Convection Cooking:
Damper is in the closed position, so that no hot air will be
allowed to leak out the oven cavity.