GB500891A - Improvements relating to telephone systems - Google Patents

Abstract

500,891. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and LONG, D. P. Oct. 11, 1937, No. 27571. [Class 40 (iv)] A hunting switch stepped by a forwarddrive magnet which interacts with its own contacts or with a stepping relay, is stopped by the closure of a local holding circuit for the magnet when the test relay operates over the test wiper. According to the Provisional Specification, the stepping relay instead of the magnet may be held. The invention is applied to the rotary movement of a bidirectional finder stepped by self-interrupting magnets VM, RM, and controlled by test relays VT, RT in an allotter. The finder is started by the application of ground to wire p, whereupon switching relay H energizes in series with RM (inoperative) and closes the vertical stepping circuit and a holding circuit for itself. Both these circuits are opened by VT when the marked level is reached. The marking potential is fed over a high resistance, while the windings of VT are of low resistance so that two such relays cannot operate in parallel. Upon operation, the holding winding is connected in a local circuit or in parallel with the operating winding to guard against the shunting effect of a test relay in another switch. With H back, the rotary stepping circuit is completed until the marked line, is reached, when test relay RT operated and holds the magnet RM in series with the right-hand winding of H. Relay H locks over its left-hand winding and short-circuits RT, causing RM to fall back. Relay VT is disconnected by means not shown and the allotter is released. When the connection is cleared. the rotary magnet, RM reoperates to step the wipers clear of the banks, after which they are restored vertically and rotarily. The test relays VT, RT are preferably of the high-speed type described in Specification 405,436, [Group XXXVII].