GB414889A - Improvements in or relating to circuit arrangements for automatically limiting the duration of an electrical process - Google Patents

Abstract

414,889. Switching systems for consuming devices. MULLER AKT.-GES., C. H. F., 24, R÷ntgenstrasse, Hamburg, Germany. July 5, 1933, Nos. 19069, 19070, and 19071. Convention dates, July 5, 1932, April 1, 1933, and April 7, 1933. [Class 38 (iv).] The duration of an electrical process, e.g. the energization of an X-ray tube, is timed by the period of charging of a condenser the charging of which controls a three electrode discharge tube the anode circuit of which includes a relay 7 controlling the electrical process to be timed. The discharge tube 1 is supplied with A.C. and the condenser 5 is charged, in one position of a switch 15 from the A.C. supply through a rectifier 9 and resistance 6, a second position of the switch 15 being arranged to open the charging circuit and short circuit the condenser 5. The grid potential of the tube 1 may be supplied by part of the transformer winding supplying the tube and by the drop across the resistance 6 which is adjustable. In this case the relay 7 is a closed circuit relay whose winding is normally energized by the current of the tube 1. Movement of the switch 15 to the position II commences the charging operation which produces a large but decreasing drop across the resistance 6 so as initially to block the valve 1 and commence the electrical process, but after a predetermined period determined by the adjustment of the resistance 6, to open the valve 1 once more and stop the process. Alternatively, the potential across the condenser 5 may be applied to control the grid voltage of the tube 1 the arrangement being such that the tube 1 is nonconducting when the condenser 5 is short circuited but is opened when the charging commences and blocked when the charging is completed. In this case the relay 7 is an open circuit relay. In a modification of the latter case the switch 15 has a third position in which the grid 3 of the valve 1 is connected to a positive bias tap on the transformer 13 supplying the tube so that the tube 1 can be made conducting at will for the purpose of energizing an X-ray tube for fluoroscopy. The charging circuit of the condenser is connected across tapping points on the winding supplying the tube 1 or to a potentiometer connected across these tappings so that the phase of the charging current coincides with that of the tube voltage. In a further modification the tube 1 is rendered positively nonconducting when the condenser is short-circuited by opening its anode to cathode circuit in this position of the switch 15. In an alternative arrangement, Fig. 5, the relay 7 has additional contacts 23, 24 which, in the energized position close its connection in the anode circuit of the valve 1 and open a short circuit across the condenser 5. Its anode circuit contacts are paralleled by a hand switch 25 by which the operation is initiated, this switch being arranged to remain closed at least until the holding contacts 24 of the relay 7 are closed.