GB685206A - Improvements in or relating to busying circuits for automatic signalling systems - Google Patents

Abstract

685,206. Automatic exchange systems. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. April 22, 1949 [April 26, 1948], No. 10742/49. Class 40 (iv). A test device which positions a finder switch on a marked contact includes a relay connected in the output circuit of a thermionic valve which becomes conductive when the marking is found, the operation of the relay busying the contact and causing the valve to revert to its original cut-off condition. As shown, tandem-connected finder switches OZ1, OZ2 have negative potential contact markings applied as described in Specification 685,295, and the switches are positioned by a test device comprising the valves B1-B4, as described in Specification 660,376. Finder switch OZ2 is started when its drive magnet D2 is energized by valve B4, which becomes conductive when starting relays B and Q (not shown) pull up. Valve B1 of the trigger-pair B1, B2 is normally non-conducting, but becomes conducting and cuts-off valve B2 when a contact marked by a negative potential derived over resistance 12 is found. Valves B3 and B4 repeat the conditions of valves B1 and B2 respectively, so that busy relay H2 is energized and the drive magnet is released. During the operating time of H2, a temporary busy marking at approximately earth potential is applied to the calling contact by an increase of potential at the cathode of valve B1. When relay H2 pulls up, a permanent busy marking is extended to the calling contact and the valves B1 to B4 revert to their original condition in readiness for a further test operation. Relay H2 also locks up and transfers the test device to finder switch OZ1 which is then started and positioned in like manner.