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Drawing 2-5(a) is the circuit and construction diagram
of the door interlock switch of a microwave oven. It
mainly consists of interlock switches (S1, S2), and
monitor switch (S3), door hook and starting mechanism
of the door interlock switch.
There fixed hooks on the oven door, and opened two
rectangle hole at the corresponding place at the right of
the oven and the hook. Inside each rectangle hole,
there fixed a micro switch. When the oven door closed,
the two hook on it would insert into the rectangle hole,
and just push down several micro switches. At that time,
S1, S2 are closed, S3 is cut off, and the microwave
oven is under preparation of working.
To that mechanical control microwave oven, no sooner
you turn the time switch to set the heating time than the
power would be supplied to the back to start the oven. To those touch
control microwave oven, hardly do you set the heating time and power,
and touch the start button when the power would supplied to the back to
start the oven.
When pressing down the door release button or pulling the door handle
to open the door, the safety interlock switches S1, S2 are cut off, and
the monitor switch S3 is closed, and the microwave oven would stop
operating immediately. Provided due to some man - made or the
appliance itself reasons, when the door is open, and the safety interlock
switches S1, S2 are not automatically cut off, due to the existence of the
monitor switch (S3) which is still at conducted condition, the monitor
switch would immediately make the 120V voltage short-circuited and
blow up the fuse, and will never let the microwave oven working when
the door is open.
From this we can understand the function of the interlock switch is
when the door is unclosed, the oven wouldn't work, when the door is
opened when the oven is working, it would stop the working
immediately (FIG.2-5b).
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Time and power distributor is mainly composed of timer motor and two
sets of gear switch S4 and S5. When the timer is at zero position, the gear switches are cut off, when the heating
time is settled, the gear switch is closed. When started
the oven, the time motor starts working. When it
reaches the settled time, it would cut off the gear
switch (s4) to step the oven working. The gear switch
(S5) is designed for controlling the output of the
microwave oven, actually for controlling the output of
the magnetron. It mainly by the method which make
the magnetron working internally at the same working
point to change the output of the magnetron. This
method was called "CONDUCTION RATIO CONTROL".
But
there
is
another method which
"ELECTRIC LEVEL CONTROL" which is through
changing the working point (such as anode voltage or magnetic field) to change the output of the magnetron.
Because of conduction ratio control method is low cost, high function and high reliability, it is widely used for
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120V
is
called
8
fuse
main latch switch
S
1
pilot switch
door closed
assistant latch switch
(a)
Fig.2-5
tch holder
itch
door hook
witch
door hook
door release button
Fig.2-5（b）
t i m e r & p o w e r m o t o r
S
S
4
5
F i g . 2 - 6
S
3
S
2
latch switch holder
latch switch
pilot switch
screw
latch switch
pilot switch
screw
t r a n s f o r m e r
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