Patent GB-761471-A (GB)
Title: Improvements in or relating to circuit arrangements for teleprinter switching installations with selection by teleprinter impulse combinations
IPC: H04L12/00
Filed: 1954-04-27
Abstract: 761,471. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES. April 27, 1954 [April 27, 1953], No. 12246/54. Class 40 (3). In a telegraph exchange system in which selection of a desired line is effected by telegraph code combinations converted into corresponding impulse sequences for controlling the digital selectors, the seizure of the exchange selecting apparatus effects the provisional starting of the motor at the subscriber station to permit the transmission of signals for the line selecting operation and the condition for the permanent operation or stopping of the motor is not established until the called subscriber's station has been reached and found to be free or engaged respectively. In the normal condition current flowing over the line and through the subscriber apparatus including transmitter contacts SK and receiving magnet EM, passes through the windings I, II of the indicator SZ, and the exchange relay R is not operated. The operation of the key AT to initiate a call short-circuits the high resistance winding SZI and relay R operates so that contact rII closes the circuit of start relay An having contact an1 in the circuit of an interrupter RU controlling a stepping magnet DAS to enable a selector WAS to find the calling line effecting the series operation of relays T, P which mask the calling line engaged, and at contacts tII, tIII switch the line to relay W in an impulse receiving circuit E whilst still maintaining on lines a, b the same polarity as in the rest condition. When at contact pIII a free line or group selector LW is found, a spacing (positive) impulse over wire b and bank WAS3 operates the armature y of relay Y to its spacing portion T and effectively opens the subscriber's line for a brief period so that the indicator SZ falls off and at released contact sz and closed contact ATII closes the circuit of relay K which at contacts KII, KIII connects the motor M to the mains N1, N2, and at contact KIV maintains the circuit for relay K when the key contact ATII is released. Contact K1 maintains the shunt of the high resistance winding SZ1. The selecting code combinations are transmitted by armature w of differential relay W to a storage and conversion apparatus S/U producing series of impulses passed by contact j of relay J of circuit JS via wiper WAS4 and normal contact dIII to the a wire leading to the selector LW. If the called line is free a long spacing impulse on line b passes via rectifier G to operate slow relay D which at contacts dI, dII and dIII, dIV connects together the called and calling lines on which the polarity is reversed by applying + TB over contacts dII, pV, AS2, tII, Lb to the polarized relay ER which operates and at contact er energizes relay H connecting at contacts hII, hIII the motor M to the lines N1, N2. Relay B is also operated so that at contact b moved to position T the transmitting relay A is connected to the calling subscriber. A slow-release relay S remains energized over contact dVI during signal transmission and relay U is operated over contacts sII and dVII. When relay D falls off in response to a long marking impulse relay S releases, opening at contact s1 the circuits of relays T, P and at contact sII breaking the circuit of relay U which later releases and at contact uI reestablishes the circuit for relay S. Also the release of relay D by the long marking potential reverses the polarity. on the subscriber's line and relay ER changes over, opening at contact er the circuit of relay H, cutting out the motor M of which the current supply cannot be reestablished until the key AT is again actuated and the connecting seuqence of operations effected. The calling subscriber can break the connection by opening key ST which effects exchange circuit operations resulting in a reversal of the polarity on the subscriber's line and stopping the motor. A modification is described in connection with Figs. 3, 4 (not shown) in which a connecting circuit (Fig. 3) and a switching circuit (Fig. 4), replace the circuit of Fig. 2 for two-wire or four-wire double-current operation in the exchange apparatus. The relays A, W of Fig. 2 which are operated differentially are replaced by polarized relays.