Electrolux EI30BM55HB - 30" Microwave Oven, Technical & Service Manual

Page: 21 / 60

Operation
2-9
(3) Detector Circuit of Humidity Sensor Circuit
This detector circuit is used to detect the output
voltage of the 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 than the detector circuit
starts to function and the LSI observes the initial
voltage available at its AN1 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 R98 ~ R102.
Changing the resistance values results in that
there is the same potential at both F-3 terminal of
the humidity sensor and AN0 terminal of the LSI.
The voltage of AN1 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 heat-
ed to generate moisture by which the resistance
balance of the bridge circuit is deviated to
increase the voltage available at AN1 terminal of
the LSI. Then the LSI observes that voltage at
AN1 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
AN1 terminal 1 6 seconds after the unit has been
put in the Sensor Cooking mode, if it is not
possible to balance the bridge circuit due to dis-
connection of the humidity sensor, ERROR will
appear on the display and cooking is stopped.
1) Humidity sensor circuit
SW1
SW2
SW3
SW4
SW5
P70
P71
P72
P73
P74
LSI
(IC1)
P66
P65
620k
300k
150k
75k
37.4k
28
31
32
26
25
30
29
47k
47k
10k
F
u
1
0.
0
F
u
1.
0
1
0.
0u
F
VA : -15V VA : -15V
0
5
R
0
6
C
1
6
C
2
6
C
9
C2
S
F-2
1.8k
F-1
F-3
C
3.57k
3.32k
VC : -5V
1.
0
F
u
C. Thermistor in
closed vessel
S. Thermistor in
open vessel
R58
R59
R50
R51
360k
R53
R52
R54
R55
D61
D60
R60
R61
R62
R57
IC2
+
-