Electrolux E30MO65GSSB, Техническое и сервисное руководство

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Operation
2-11
Humidity Sensor Circuit
(1) Structure of Absolute Humidity Sensor:
The absolute humidity sensor includes two thermistors as
shown in the illustration below. One thermistor is housed
in the closed vessel filled with dry air while another in
is the open vessel. Each sensor is provided with the
protective cover made of metal mesh to be protected
from the external airflow.
2) Operational Principle of Absolute Humidity Sensor:
The figure below shows the basic structure of an
absolute humidity sensor. A bridge circuit is formed by
two thermistors and two resistors (R1 and R2).
The output of the bridge circuit is to be amplified by the
operational amplifier. Each thermistor is supplied with
a current to keep it heated at about 150°C (302°F),
the resultant heat is dissipated in the air and if the two
thermistors are placed in different humidity conditions
they show different degrees of heat conductivity leading
to a potential difference between them, causing an output
voltage from the bridge circuit, the intensity of which is
increased as the absolute humidity of the air increases.
Since the output is very minute, it is amplified by the
operational amplifier.
Ventilation
openings
View of sensor case removed
Sensing part
(Open vessel)
Sensing part
(Closed vessel)
Sensing part
(Open vessel)
Sensing part
(Closed vessel)
Cross section view
Sensor
Case
Thermistor
Element
Thermistor
Element
C
S
R3
R1
R2
+
-
Operational
amplifier
Output
voltage
S : Thermistor
open vessel
C : Thermistor
closed vessel
2 Absolute humidity (g/m )
O
utpu
t v
o
ltage
Absolute humidity vs,
output voltage characterist
Figure 2-8. Humidity Sensor Operation
Figure 2-7. Humidity Sensor
(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
first, 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
0.01µ
F
0.
0
1
5µ
F
0
.0
1µF
360k
+
-
1 12
VA : -15V
VA : -15V
R
51
9
S
F-2
10
1.8k
F-1
F-3
C
11
3.57k
3.32k
VC : -5V
0.1 µ
F
C. Thermistor in
closed vesssl
S. Thermistor in
open vessel
IC2(IZA495DR)