-8470
R-8570
ABSOLUTE HUMIDITY SENSOR CIRCUIT (R-8570
The absolute humidity sensor includes two
thermistors as shown in the illustration. One
thermister is housed in the closed vessel filled with
dry air while another in the open vessel. Each
sensor is provided with the protective cover mode
of metal mesh to be protected from the external
airflow.
Internal Structure of
The figer below shows the basic structure of an
absolute humidity sensor.
A bridge circuit is
by two thermistors and two resistors (RI
and R2).
The output of the bridge circuit is to be amplified
by the operational amplifier.
Each thermister is supplied with a current to keep
itself heated at about 150
(302 “F) and the re-
sultant heat is dissipated in the air and if the two
thermistors are placed in different humidity condi-
tions they
show different degrees
o f h e a t
leading to 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 will be amplified by the
operational amplifier.
This detector circuit is used to detect the output
voltage of the a absolute humidity circuit to allow
the LSI to control the sensor cooking of the unit.
When the unit is set in the sensor cooking mode,
16 seconds later the detector circuit starts to func-
tion and the LSI observes the initial voltage
availabel at its AN2 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.
Changing the resistance values results in that
there is the same potential at both F-3 terminal of
the absolute humidity sensor and AN3 terminal of
the
The voltage of AN2 terminal will indicate
about
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 bal-
ance of the bridge circuit is deviated to increase the
voltage available at AN2 terminal of the LSI. Then
the LSI observes that voltage at AN2 terminal and
compares it with its initial value, and when the
comparison rate reaches the prest value (fixed for
each menu to be cooked), the LSI causes the unit
to stop the sensor cooking; thereafter, the unit gets
in the next necessary operation automatically.
When the LSI starts to detect the initial voltage at
AN2 terminal 16 seconds after the unit has been
put in the Sensor Cooking mode, if it is impossible
to take a balance of the bridge circuit due to dis-
connection of the absolute humidity sensor, ER-
ROR will reappear on the display and the cooking
is stopped.
1
humidity sensor circuit
c
. .
23
t
I
,
2)lnternal equivalent circuit of
Top View
27
Summary of Contents for R-8470
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Page 50: ...R 8470 R 8570 1 2 3 j 4 5 6 I CABINET PARTS I 1 I 1 I 2 I 3 I 4 I I 5 6 48 ...
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Page 53: ...R 8470 R 8570 1 2 I 3 I 4 5 6 DOOR ASSEMBLY MISCELLANEOUS 6 3 Trans m I I I I I I i I t ...
