| 摘要 |
1,157,194. Automatic temperature control systems. HIRST (MICROWAVE HEATING) Ltd March 14, 1968 [April 5, 1967], No.15569/67. Heading G3R. To compensate for the heating effect of electronic bombardment of a magnetron cathode, the cathodic radiation is sensed by a photosensitive cell 20 which regulates the cathode heater current. A photo-resistive cell 20 sensing cathodic radiation is connected across a capacitor 21 forming one arm of a bridge circuit having other arms 24-28 controlling, through a transistor 30, the charging current of a capacitor 32 from a synchronized squarewave supply 37-40. The capacitor 32 is periodically discharged by a unijunction transistor 35 through a winding of a transformer 33 which supplies firing pulses to thyristors 17, the angle of conduction being determined by the resistance of cell 20. The heater supply 18, 19 has an NTC resistor 16 in series to limit the initial heater current to twice normal. The arrangement is stated to allow a greater degree of mismatch between a magnetron and a load than would otherwise be possible without deterioration of the magnetron. Where the magnetron output is fed to a continuously moving sheet which, if it suddenly comes to an end, no longer provides an absorptive load, a sudden increase in the reflected power incident on the magnetron cathode is compensated. The magnetron envelope has window which admits radiation from the cathode to the cell. |
