Patent GB-351490-A (GB)
Title: Step-by-step private automatic exchange system employing common control apparatus
IPC: H04Q3/00
Filed: 1930-03-26
Abstract: 351,490. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., LOWRY, L. P., and BALL, W. S., Columbia House, Aldwych, London. March 26, 1930, No. 9642. [Class 40 (iv).] In a system using unidirectional step-by-step type switches, connections are established over link circuits comprising a line finder permanently associated with a connector, the link circuit being preselected by a control circuit common to several link circuits, which responds to the dialled digits and marks the wanted line. The control circuit comprises two auxiliary switches, one of which marks lines or groups of lines in banks of the second switch which in turn marks the wanted line, the first switch then moving to find the preselected link circuit to enable the connector to hunt for the marked line. The system is described as applied to a 100-line exchange. Seizure of control circuit. When a call is originated L operates its light armatures l1, l2 energizing relay SA and relay A, in the preselected control circuit, operates over ra5, rb1, as1. Relay B pulls up and D operates marking the circuit busy to other control circuits and allowing LF to search for the calling line. When this line is reached L operates fully in series with BB which latter relay locks to b3. Relay BB steps the allotter switch AS in search of another free control circuit, connects relay A over the subscribers loop and connects dial tone from DT to the calling subscriber. Registration of digits. The first digit train is repeated by A to magnet RA and switch RA steps, marking, over wiper ra7, terminals in bank rb1 of RB. Relay C energizes in series with RA and as soon as RA moves off normal RB steps by self-interruption over wiper ra3. When the first train has finished C releases and when wiper rb1 reaches the terminal marked by ra7, M energizes stopping the automatic movement of RB. With M energized and C back relay G pulls up completing a circuit to move RA to its eleventh position. Relay M de-energizes as soon as RA commences this second movement. The second digit is repeated by A to RA as before, and RB moves forward as soon as RA steps off normal moving its wipers to the terminals marked by wiper RA7. When the impulsing ceases C releases and when the marked line is reached M energizes over wipers ra7, rb1. During the first marking operation wiper ra7 marks the same terminal in the bank of rb1 for two positions of RA. Contacts 2, 4, 6, 8, 10 of ra1 are, however, connected together and to relay J and consequently if the first digit is odd relay J operates and locks changing over the marking and testing circuits from wipers RB2, RB4 to RB3, RB5. This enables a 100 point connector to work from a 50 point secondary marking switch. Setting of connector, testing called line, ringing, release. The energization of M completes a circuit for E which energizes, releasing M and completing a stepping circuit for RA. Switch RA steps until wiper ra1 encounters the circuit marked over cf6 when T pulls up, breaking the circuit of RA and completing a circuit for magnet LS to step the connector in search of the line marked by rb2 if the tens digit is even and rb3 if the digit is odd. When the marked line is reached M re-energizes operating BS which connects the calling line to the link circuit and AS pulls up. If the called line is busy earth on ls3 shorts PH over rb4 or 5, GS remains de-energized and Busy Tone from BT is connected to the calling line. If the called line is free, however, PH energizes from battery over the called subscriber's line relay, GS operates, and ringing from RG is suppled to the wanted subscriber. When the called party replies FS energizes switching through the connection, and DS pulls up to provide an additional holding circuit for GS. When the parties release relays GS, BS, AS, FS, DS release. Called party held alarm is provided. Release of control circuit. On the operation of BS when the required line had been found A released followed by B, E, T, D. Switch CF steps to find another free link circuit and switches RA and RB restore to normal. Prevention of crossed connections. If only two control circuits are provided the connections to relays M in the two circuits are reversed. If more than two such circuits are provided the lead from wiper rb2 (or 3) is broken at points x1, x2 and these points are wired to banks td2, td3, Fig. 3. The switch TD stops to connect these points when relay E and not relay PH is energized and the points can therefore be connected for only one control circuit at one time. Alternative arrangement. A system is also described in which the switch RB is replaced by two 50 point switches marking respectively the first and second 50 lines in the connector, in which the RB switches respond directly to the second dialled digit and in which two groups of lines are provided, the preselector moving on to find a suitable finder if the link preselected does not give access to the calling line.