Pa=KE
fErtg
5
Pa Stands for the power the heated
matter
adsorbed
from
the microwave
field.
K Stands for a constant
E Stands for the
microwave
frequency.
f Stands for the microwave
frequency.
tg 6 Stands for
loss
angle
tangent of the heated matter.
Er Stands for relative dielectric constant of the heated matter.
High
Voltage
Rectifier
220V
r
2 THE STRUCTURE AND
WORKING
PRINCIPLE
OF
MICROWWAVE
QVEN.
Microwave oven can be classified to
many
kinds
according to
various
construction,
volume and control
function. But anyhow, the
main
electric
parts
arę
all
composed of high voltage
rectification,
cooling system.
Microwave generator, electric control system and heating
chamber
(FIG.2-1).
Its
working process
arę
as follows:
220V power frequency voltage transferred to the rectifier
through electric control
system,
and then be changed to
4000V direct volt-age by the rectifier, and be then
transferred to the microwave generator, the generator
stars working to transfer the microwave energy to the
heating chamber for heating food through wave guide
tubę.
At the same time, the electric control system set off
the cooling system to
cool
the working rectifier and the
microwave generator to keep the oven working steadily
from a too high temperaturę.
If
something wrong with the
cooling system cause the temperaturę too high, the control system would cut off the power automatically to
prevent microwave generator being damaged form the high temperaturę.
Nów,
we'd
like
to introduce the working
principle of each
part
of the widely used model, mechanical control and touch control microwave oven.
2,1 HIGH
VOLTAGE
RECIIFYING
CIRCUIT.
At present,
home
use microwave oven adopt this high voltage
rectifying
circuit as shown at diagram 2-2.The
circuit is a single phase, semi-wave, double voltage rectifying circuit. The circuit has
only
a high voltage capacitor,
a high voltage diodę, a magnetic leakage transformer besides the magnetron, is
very
simple.
The working principle of the circuit: 220V power boosted through the transformer, output about 2000V alternating
high voltage current when the high voltage winding is at the positive half-circle, the high voltage winding is at the
negative
half-circle,
the diodę is cut off and the magnetron is conducted. The
electricity
charged at the positive
half-circle of the capacitor is series connected with the positive phase of the winding
voltage,
and got a doubled,
about 4000V direct high voltage, then transferred to
between
the cathode and the anodę of the magnetron.
Electric
Control
220V
Fig.
2-2
Fig.
2-3
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