GB573469A - Improvements in safety systems for electrical control of machinery - Google Patents

Abstract

573,469. Machinery safety devices. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 27, 1943. No. 1366.. Convention date, Jan. 29, 1942. [Class 80 (iv)] [Also in Group XXXV] Relates to safety systems for the control of machinery requiring a plurality of electrical or mechanical devices tobe operated or simultaneously operated before a controlled element is energized, or to machines in which both hands of the worker are required to initiate operation. A relay or other electrically-responsive element 20, adapted to start machinery by closing an electrical circuit 26 or by other means, is controlled by two or more switches 12, 13 which in their unoperated condition establish jointly the charging circuit of a condenser 18 and when all are operated cause the condenser to discharge through the relay. By connecting a resistance 27 in parallel with the condenser the relay will not be energized unless the switches are operated substantially simultaneously. The period of energization of the relay is determined by the capacity of the condenser and the impedance of the relay, and to assure that this timing is not interfered with by release of a switch an auxiliary normally open contact 29 may establish an independent discharge circuit through the relay. To secure complete discharge of the condenser before a subsequent operation the relay may have an auxiliary normally closed contact 28 in the charging circuit. A further auxiliary normally closed contact 30 may interrupt the circuit through the resistance.