GB780982A - Improvements in and relating to electric switching apparatus - Google Patents

Abstract

780,982. X-ray timers. GENERAL ELECTRIC CO. July 14, 1954 [July 14, 1953], No. 20601/54. Class 40 (3). [Also in Group XXXV] A contactor 30 controlling the high-tension supply to an X-ray tube 11 is closed following operation of a push-button 58, by conduction of a hard valve 61 controlled by a thyratron 66 and is subsequently opened, to terminate exposure, by operation of a contactor 41 which causes the valve to become non-conducting and which operates in response to conduction of a thyratron 42 controlled by an integrating exposure meter 38, 40. Operation of the pushbutton energizes a contactor 51 which, at contacts 53, prepares a circuit for energizing contactor 41 from a source 46 and, at contacts 54, prepares a circuit for energizing contactor 30 from a source 60. The anode circuit of thyratron 66 is also completed at contact 55, whilst operation of contacts 56, 57 modifies the bias applied to this tube which is then fired by an adjustably phased pulse applied over rectifiers 78, 78<SP>1</SP> supplied from a phase-shifting network 73-76. The voltage developed across a resistor 67 in the cathode lead of thyratron 66 is applied as positive bias to the hard valve 61 which thereupon conducts and closes contactor 30 to initiate exposure. Thyratron 42 is subsequently fired by the output voltage of meter 38, 40 and energizes contactor 41 which opens its contacts 48 to disconnect resistor 67 from the grid of valve 61. The valve ceases to conduct, contactor 30 is de-energized and the exposure terminated. By adjustment of the mechanical and electrical constants of the several contactors, adjustment of the phase of the firing pulses applied to thyratron 66 and adjustment of a time constant circuit 64, 65 associated with the grid of valve 61, the contactor 30 may be caused to close and open at current zero points in the supply cycle. In a modified system, the contactor 41 has normally open contacts and is energized to close its contacts upon operation of the push-button-controlled contactor 51. When thyratron 42 is rendered conducting it becomes a low resistance shunt on contactor 41 which, in consequence, drops out and opens its contacts. Specifications 747,722 and 752,971 are referred to.