GB519192A - Improvements in or relating to electric apparatus for timing the period of energisation of a given device - Google Patents

Abstract

519,192. Switching systems. IGRANIC ELECTRIC CO., Ltd. (Cutler-Hammer Inc.). Sept. 16, 1938, No. 27070. [Class 38 (iv)] [Also in Group XXXVII] A circuit 5a which may for example control a welding circuit 1 is energized for a predetermined 'time by the momentary depression of a push-button 2, the time being determined by the rate of discharge of a condenser 4. On depressing the button 2 a circuit is completed through a relay 7a and another circuit through contact 3a and the relay 5a. The relay 5a operates to close contacts 5b, completing the circuit to the welding transformer 6, and contacts 5c in a maintaining circuit. The relay 7a closes contact 7b, thereby completing a circuit through a rectifier 8 to the winding 3b of a relay 3, and opens contacts 7c thereby breaking the rectified current that has previously energized a winding 3c of the relay 3. The decay of current in 3c, is how ever delayed by the discharge from the condenser 4 and only after a time interval does the relay 3 operate to break the. circuit to relay 5a. which thereupon opens contacts 5b, and breaks the welding circuit. An adjustable resistance 9 enables the time of weld to be varied. In a modification, Fig. 2 (not shown), there is an additional winding in opposition to the winding 3c and energized from the circuit 5b, 6, i.e. by current proportional to the welding current. This causes the relay to operate earlier when there is a big welding current and thus serves to maintain the energy of each weld substantially constant. In a further modification, Fig. 3 (not shown), the relay 3 has, in addition to the two windings of Fig. 1, a third winding acting on the upper limb of the armature and serving to hold the armature in position after it has operated. There is also an additional two way switch. When this switch is in one position, the device operates as in.Fig. 1. When the switch is in the other position, if the push button is held depressed, a continuous series of welds is produced, the time of each weld being determined as before by the discharge of the condenser 4 and the time between welds being determined by the dying away of current in the third inductive winding due to its being short-circuited by a circuit with a variable resistance in it. This occurs immediately the relay 3 operates, the winding 3b being simultaneously de-energized and the winding 3c energized so as to tend to return the relay to its original position.