Jenn-Air JMD2124WS Technical Education - page 20
3-4
(3) Detector Circuit of 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 than 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 R45 ~ R49. Changing
the resistance values results in that there
is the same potential at both F-3 terminal
of the absolute humidity sensor and AN6
terminal of the LSI. The voltage of AN7
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
S
C
R3
R1
R2
+
Operational
amplifier
Output
voltage
S : Thermistor
open vessel
C : Thermistor
closed vessel
2
Absolute humidity (g/m )
O
eg
atl
ov
tu
pt
u
Absolute humidity vs,
output voltage characteristic
R43 1.8K
VA : +15V
VC : +5V
R42
3.57K
R41
3.32K
S
C
R51 47K
R45 620K
R46 300K
R47 150K
R48 75K
R49 37.4K
R44 360K
R50 10K
3
F2
8
4
1
2
IC5
+
-
R40
430
C42
0.1µ
F
D40
D41
R52 47K
86
63
P04
P03
P02
P01
P00
AN6
SW1
SW2
SW3
SW4
SW5
AN7
LSI
(IC1)
64
52
51
50
49
48
C. Thermistor in
closed vessel
S. Thermistor in
open vessel
F3
F1
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 AN7 terminal and com-
pares 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 cook
ing; thereafter, the unit goes in the next
operation automatically.
When the LSI starts to detect the initial
voltage at AN7 terminal 16 seconds after
the unit has been put in the Sensor Cook
ing mode, if it is not possible to balance
the bridge circuit due to disconnection of
the absolute humidity sensor, ERROR will
appear on the display and the cooking is
stopped.
THE ABSOLUTE HUMIDITY (AH) SENSOR CIRCUIT (cont'd)