2.2MICROWAVE GENERATER.
Microwave generator is the heart of microwave oven. The quality of a microwave oven mostly depends on the quality of the microwave generator. A microwave generator is mainly composed of magnetron and its power supply circuit,
Usually, we adopt continuous wave magnetron. It can turn the direct energy which is applied to the magnetron after being high voltage rectified to microwave energy, the power supply circuit supply a direct high voltage between the cathode and anode of the magnetron, a filament voltage to the cathode filament of the magnetron.
The working process of the magnetron: When the anode
If the anode voltage is undulating, it would cause the anode current swing fiercely, even made the magnetron stop oscillating. For keeping a steady output, the power supply circuit of the oven must supply a stead direct current voltage. The filament voltage of the magnetron must be supplied by an alternating current voltage. For simplifying the circuit, it would be supplied by the same leakage magnetic transformer with the anode power (high voltage power). The filament of the magnetron which the present used microwave ovens are all treated through some special technology, and all have the cold start character. But when in cold start, there still is a very strong surge electric field attached to the surface of the anode, and would be harmful to the anode. In order to reduce the surge voltage, the filament of the magnetron must be connected as the
)Vk (mb e
voltageanode
anode current
Ib(mA)
Fig.2-4
2.3COOLING SYSTEM
In the working process of the microwave oven, the magnetron often makes the anode temperature rise due to anode loss
caused by the electronics strike the oven surface and the heat radiate of the cathode. To prevent the anode temperature rise too high, thus affect the working steady and its life span, it is necessary to cool the magnetron. According to the different models and rate output of the magnetron, compelling wind cooling and flowing
Cooling system includes fan motor, air duct, air entrance, air vent etc. The flowing direction of the cooling wind should. Be parallel to the cooling fin of the magnetron. Generally, we adopt the method of air blast rather than air absorb. And all the cabinet of the oven is with air entrance and air vent, the hot wind blowing through the magnetron is guided with air tube to improve the cooling effect. In the technical parameter chart of the magnetron, it usually will give out the requirement of cooling wind. A shortage of cooling wind would damage the character of the magnetron, even burn out the magnetron. The amount that the fan blasted should not be less than the requirement. When fix the fan, attention must be paid to prevent the cool wind from blowing directly to the glass part of the magnetron to avoid blasting.
2.4ELECTRIC CONTROL SYSTEM.
To those mechanical control microwave oven, electric control system mainly composes of interlock switch, timer, power distributor and thermal cutout, etc. The electric control system of those tough control microwave oven is mainly composed of interlock switch, computer controller and thermal cutout, etc.
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