Improvements in or relating to short-time switches operating with the aid of controlled current converters

Abstract

Abstract 487,982. Valve circuits ; control systems for resistance welding. SIEMENSSCHUCKERTWERKE AKT.-GES. July 2, 1937, No. 18495. Convention date, July 2, 1936. [Class 40 (v)] [Also in Group XXXV] A controlled current converter of the gridcontrolled mercury vapour type is ignited by applying to its control grid a gradually increasing positive potential derived from the charging or discharging of a condenser and superimposing thereon an A.C. potential of pointed wave-form. Fig. 1 shows a short-time switching arrangement for spot or seam welding apparatus, in which the current from D.C. mains 1 is applied across two grid-controlled mercury vapour tubes 3, 5 through a switch 2. The grid bias of the auxiliary valve 3 comprises a fixed source on which is impressed an A.C. potential of pointed wave-form from transformer 6. When the switch 2 is closed valve 3 is energized and a voltage is built up across resistance 4 in the work circuit. The grid circuit of the main discharge tube 5 comprises biassing resistance 7, condenser 8, charged from source 1 through variable resistance 10, and a source 9 of A.C. potential of pointed wave-form. As soon as switch 2 is closed condenser 8 becomes charged up ; when its voltage added to the voltage peaks from 9 exceeds the required ignition voltage (e.g. in 3 cycles) tube 5 strikes and short circuits resistance 4 to remove effectively the voltage applied to the work circuit. If the source 9 were not provided, the time taken for tube 5 to strike would vary with different tubes used in the circuit, due to slight variation of ignition-voltage characteristic ; the provision of source 9 ensures that ignition takes place at exactly the same time interval from rest even with variations of + 2 volts in the tube ignition voltage.

Inventors

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