| 摘要 |
A microwave oven includes a heating chamber, a turntable provided in the oven, a magnetron, a waveguide for guiding the microwave generated by the magnetron into the heating chamber, an electric field sensor provided at the inner wall face of the waveguide or the heating chamber, a metal reflector provided rotatably inside the waveguide for adjusting the impedance of a load at the heating chamber side by its rotation angle, and a circuit responsive to an output of the electric field sensor for controlling the rotation angle of the metal reflector. The control circuit includes a first program for controlling the rotation angle of the metal reflector according to a first method within a predetermined time period from the start of operation of the microwave oven, and a second program for controlling the rotation angle of the metal reflector according to a second method different from the first method after elapse of the predetermined time period. For example, in the first method, the rotation angle of the metal reflector is sequentially controlled so that the output of the electric field sensor is minimum, and in the second method, the rotation angle of the metal reflector is fixed to an average value of the rotation angle of the metal reflector of the first method. The initial rotation angle of the metal reflector is determined so that impedance matching can be obtained when load of approximately 300-500 cc calculated in water load is placed at the center of the heating chamber.
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