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NE-972
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4. Convection cooking control (
)
The digital programmer circuit controls the ON-OFF time of convec-
tion and grill heaters which are located at rear and top of oven cavity
respectively in order to control oven cavity temperature.
Normal Convection Cooking
(A) After the start pad is tapped with the desired normal convection prog-
ramme set, an 18V DC signal comes out of the digital programmer
circuit and is applied to the coils of power relays 2 and 3.
(B) When power relays 2 and 3 energize, power source voltage (240V
AC) is applied to both convection and grill heaters and oven tempera-
ture starts increasing.
(C) When the oven temperature reaches the set temperature, the digital
programmer circuit senses the temperature through oven temp sen-
sor and stops supplying an 18V DC signal to the power relays 2 and 3
resulting in both convection and grill heaters to turn off.
After the heaters turn off, the oven temperature will continue increas-
ing a while then decrease as shown in Fig. 4.
(D) When the oven temperature drops below the set temperature, the
digital programmer
circuit senses the oven temperature
and starts
supplying an 18V DC signal to the coils of power relays 2 and 3 again.
Note that grill heater (power relay 2) tums on and off alternatively at
predetermined duty cycle (7 sec ON, 15 sec OFF) until oven temper-
ature reaches set temperature again by the signal from digital prog-
rammer circuit. (Fig. 4)
Conv. Heater
(Power Relay 3)
Grill Heater
(Power Relay 2)
Grill Heater
(Power Relay 2)
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Microwave
Oven Lamp
(Power Relay 6)
Turntable
Fan Motor
Dual Shelves Convection Cooking (
)
When the start pad is tapped with dual shelves convection cooking fea-
ture selected;
(A) The digital programmer circuit generates the 18V DC of 20 sec ON, 2
sec OFF signats for convection heater (power relay 3) and continued
High signal for grill heater (power relay 2) as shown in Fig. 4 so that
both heaters turn on to increase oven cavity temperature.
(B) When
the oven temperature reaches set temperature, the digital
programmer circuit stops supplying the 18V DC signals to turn both
heaters off.
(C) When
the oven temperature
drops below the set temperature, the
digital programmer circuit starts to supply the 18V DC signals again
but at different duty ratio as shown in Fig. 4.
NOTE: See Fig. 4 for operating sequences of microwave, tumtable, fan
and convection fan motors during convection cooking mode.
(Triac)
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ON (slow)
i
Convection Motor
ac
OC [Rs
Fig. 4
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