power control
is the power control circuit diagram of brand microwave oven, WP700. This is a typical instance of
ratio control. This oven adopt
and power controller as a
When a 220V, 50Hz alternating
current is
the time and power motor is always at working condition. At the
S5 is always
the S5 working 30 seconds as a circle, the conduct time can be successively adjusted
5
seconds to 30 seconds. When power select switch is set at
S5 is always
the output of the
microwave oven is
power) when the power select switch is set at defrost position, S5
conduct for
14.4 seconds, and cut
for
and the average output of the oven is 336W.
2.4.3 THERMAL
Thermal cutout actually is a thermal sensor switch, usually, it is fixed on the
of the magnetron, and series
connected
the
circuit of the magnetron to control the power input. At
condition, the thermal
cutout is always conducted
When something wrong with the cooling system that cause some abnormal
conditions, such as molding or thermal breakdown,
the temperaturę of the magnetron reach the limit
value. Then, the thermal cutout would work to turn off the power to prevent the magnetron from
damaged.
2.4.4 HEATING
Heating chamber is the place where the microwave and the food
mutually.
of chamber.
Accord-ing to the working characters, it can be classified to
type, cavity type, radiation type,
type
wave type), etc. The present adopt chamber for food
microwave oven is the typical carton type
heating. (FIG.2-8). The heating chamber is mainly composed of oven door and oven cavity. From the microwave
it is a microwave resonant cavity that can contain
kinds of oscillating models
Microwave enters into the oven
through the wave
and the coupling
and most of its energy
is absorbed by the food
it is reflected in the
those which
been absorbed will be
reflect to the magnetron. A good designed oven cavity should have a good impedance matching with the
magnetron, the energy should be less reflect, and distribute evenly in the oven cavity, improve the heating
Generally, at the same input power, the larger the cavity, the less the energy density a unit volume
would
in the oven, and the
energy on the inside
of the cavity would
thence, it would
down the heating speed, Iow the heating efficiency.
too big of the
would either waste the
materiał or appears
heavy. The materiał for
usually use non - magnetic stainless
or zinc - plating
and have no high requirements for the conducting
The inside
of the cavity
beautiful in
durable when use (should be resistant against
heat, acid and alkali), it should
comply with the
food health requirements.
Safety interlock switch
2. Door
3. Air vent
4. Roller
5. Turntable
6.
tray
7. control panel
To improve the heating evenness there
fixed a turntable
tray at the bottom of the
(FIG. 2-8). It is
through changing the relative place of the microwave and the heating
to improve the heating evenness.
The turntable tray is usually
of heat - resistant
the glass contains some dielectric
it can,
somewhat, protect the magnetron when the cavity loading less.
There often fixed a dust -
Iow - loss and heat - resistant dielectric cover (such as
sheet).
an impedance matching metal stick was fixed near the coupling or in the wave guide.
The door is designed for
taking and
the heating food, it is also one side of the cavity (FIG .2 -
l
