Fire Sensing Feature - Electrolux ICON E30SO75ESS Technical & Service Manual

Operation
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. ROAST PAD TOUCHED.
3. COOKING TIME PROGRAMMED.
4. "START" PAD TOUCHED.
BLK
Fuse
20A
GRN
GND
WHT
Notes:
1. Circuits/ Wire colors subject to change without notice.
FIRE SENSING FEATURE (MICROWAVE MODE)
This model incorporates a sensing feature which will stop
the oven's operation if there is a fire in the oven cavity
during microwave cooking. This fire sensing feature will
operate when the microwave power level is set to 80% or
more. This is accomplished by the LSI repeatedly
measuring voltage across the temperature measurement
circuit (thermistor) during it's 32-seconds time base and
comparing the obtained voltage measurements. If the
most recent voltage measured is 300 mV greater than the
previous voltage measured, the LSI judges it as a fire in
the oven cavity and switches off the relays to the power
transformer, fan motor and convection motor. The LSI
also stops counting down and closes the damper door so
that no fresh air will enter the oven cavity. Please refer to
the following section for a more detailed description.
Operation
Please refer to the timing diagrams.
1. The fire sensing will start after 30 minutes when the
oven is started.
2. The thermistor operates within a 32-seconds time
base and it is energized for three (3) seconds and off
for 29 seconds. Two (2) seconds after thermistor is
energized, the voltage across the temperature
measurement circuit is sampled by the LSI and
twenty five (25) seconds after the thermistor is cut
NOTE: The solid-state relays and relay RY2 are energized alternately.
For last 15 minutes, the contacts of relay RY6 will contact D5.
Red
LV T T ransformer
T1
A A 1 1 A 3 T7 T6 T4 T3 T2
Fuse 12.5A
Control Unit
BLK
BRN GRN WHT
GRN
GRN
GRY
Figure 2-5. Oven Schematic-Speed Roast Cooking Condition
Red
MG
Temp. Fuse
Side Heater
Thermal
Cut-out
BRN
Red BLK
Top Heater
Thermal
Cut-out
D9
RY6
BLK
N.O.
COM.
WHT
GRY Secondary
Interlock Switch
GRY WHT
off, the LSI turns on the convection fan for three (3)
seconds.
3. The above procedure is repeated. If the difference
between the first voltage measured (in step 1) and
the voltage measured when the procedure is repeat-
ed (step 2) is greater than 300 mV the LSI makes the
judgment that there is a fire in the oven cavity and
will switch off the relays to the power transformer,
fan motor and convection motor. The LSI also stops
counting down and closes the damper door so that
no fresh air will enter the oven cavity.
4. Once the fire sensor feature has shut the unit down,
the programmed cooking cycle may be resumed by
pressing the START pad or the unit may be reset by
pressing the CLEAR pad.
0 2 3
ON
CONVECTION
MOTOR
OFF
ON
THERMISTOR
OFF
ON
Sensing
Voltage
OFF
Sensing the voltage across temperature measurement circuit.
2-6
BLK
BLK
BLK
Fuse
F10A
Solid-State Relay
ORG
Red
BRN
BRN
BLK
RED
BRN
Solid-State Relay
28 31 32 (sec.)
3 sec.
3 sec.
64 (sec.)