IE32338L - Regulation of electron guns - Google Patents

Abstract

1,202,811. 811. Automatic control systems for electron beam furnaces. AIR REDUCTION CO. Inc. April 25, 1968 [May 3, 1967], No.19543/68. Heading G3R. [Also in Division H2] An electron beam furnace is provided with a regulated power supply which includes a protective circuit responsive to arcing in the furnace as evidenced by a rapid rise in operating current to a trigger level, the protective circuit operating firstly to reduce the current to a level sufficient to starve the arc within a period of time which is preferably within 15 milliseconds from the time the current reaches the trigger level and subsequently automatically to restore the current. As shown, an electron beam furnace 14 is supplied from a D.C. source 28 by way of a resistor 46, a series valve 16 and a transductor 122. The normal operating current, as sensed by the transductor 122, is maintained at a desired value by a control system 26 which operates in known manner to regulate the heating current supplied to the filament of the electron gun 12. The operating voltage is maintained constant by controlling the bias applied to the grid 20 of the valve 16 in dependence upon an error signal derived from a control circuit including a voltage sensing network 18, an isolating transformer 94 associated with converters 90, 98, a voltage regulator 102 which may be of the series transistor type, and a normally closed switching circuit 22. Thus in normal operating conditions both the voltage and current supplied to the furnace are controlled at desired values, but when arcing occurs the operating current rises rapidly; this condition is detected by a sensor 24 which is connected across the series resistor 46 and which produces one output for application to the switching circuit 22 and another output for application to a restart circuit 114. When the rising current reaches a predetermined trigger level the switching circuit 22 opens to render the valve 16 much less conductive, whereby, within 15 milliseconds, the current is reduced to a level sufficient to starve the arc; subsequently, and after a predetermined period, e.g. less than 10 milliseconds, a signal from the restart circuit 114 closes the switching circuit 22 and the operating current is restored. Should the arc still persist the switching circuit 22 is again opened and the cycle repeats until the arc is extinguished. Suitable arrangements, including transistors and thyristors, for the circuits 22, 24 and 114 are described with reference to Fig. 2 (not shown). [GB1202811A]