Patent GB-401811-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone exchange systems
IPC: H04Q3/00
Filed: 1932-07-13
Abstract: 401,811. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and COLLYER, J. E., c/o General Electric Co., Stoke, Coventry. July 13, 1932, No. 19795. [Class 40 (iv).] In a selector which hunts for an idle or marked outlet, the outlets are provided with a test wire distinct from the usual private wire and connected to the bank of an additional test wiper one step ahead of the speaking and private wires, so that an advance test is made. When an outlet is seized, the selector takes a further step and the usual backward controls are exercised over the private wire. The private and test wires may be interconnected through a rectifier and contacts of the switching relay of the succeeding selector. The system described employs single-motion selectors with common control apparatus at each stage, the arrangement being such that impulses may be received in the common apparatus before the associating switch has completed its operation. Non-numerical link, Figs. 1, 2. Line relay L connects up start relay S and marks the calling line. Relay P operates in each of the two allotters, and two finders are started. When the finder LF reaches the position marked by L in bank LF4, SD energizes, holds magnet LF and starts the switch SF in search of an idle first selector. This is denoted by battery in bank SF4, and when found, SE energizes, holds magnet SF and connects up Z, whereupon magnet SF releases and advances the switch SF into engagement with the seized first selector. Switching relay KF energizes over wiper SF3, and magnet LF releases and advances the finder LF into engagement with the calling line. Line relay L falls back followed by S, P, Z and the allotter AS advances to the next idle link. First selector, Figs. 3, 4. Common line relay A energizes and connects up B, CA, CT, the control circuit and first selectors being marked busy. The associating switch FF steps to the position marked in bank FF2, when X pulls up and holds magnet FF in series with Y, which releases magnet FF to advance the switch a further step and returns earth over wire p to hold KF and K. Incoming impulses, which may be received while the switch FF is stepping, are repeated to set the digit switch DR, and at the second step of the latter, M energizes momentarily and sends a starting impulse to the magnet GS of the selector, which continues to step over self-interrupting contacts. Assuming the digit is 4, the last terminal of the second group is marked in bank GS2, and M energizes when the selector reaches this position, holding magnet GS, connecting up magnet DR and releasing CA which in turn releases M. Magnet GS therefore continues stepping, while magnet DR advances the digit switch one step to mark the end of the third or wanted group. Test relays SY, SZ are connected to wipers GS3, GS4, and one or other energizes when an idle second selector is found, the former having preference. Assuming SZ energizes, magnet GS is held and SA operates, connecting switching relay HB in series with SZ. HB releases magnet GS which steps the selector into engagement with the seized second selector, and disconnects common line relay A to free the control circuit. If all the outlets of the group are busy, in the last position, magnet GS remains held in series with BB, which supplies busy tone and connects up SA to release magnet GS. If no impulses are received, relays PS, AL are energized by time pulses, and connect up switching relays HA, HB which free the control circuit. The selector is marked busy, a lamp PG being lighted, and HB remains held over the line loop. Second selector, Figs. 5, 6. Line and release relays AJ, BJ energize, followed by AC, BC, CTC in the control circuit. The associating switch CD steps into engagement with the seized selector under control of relays XC, YC as in Fig. 4. Meanwhile, impulses are repeated by AJ, AC to set the digit switch DD, and the selector DK seizes an idle final selector in the wanted group in the manner described with reference to Figs. 3, 4. Subsequent impulse trains are repeated forward by AJ over the positive wire. Final selector, Figs. 7, 8. Common line relay AF energizes, followed by BF, and the associating switch DF operates as in Fig. 4. The tens digit is registered on the switch DG, and the units digit on the switch DH, changeover relay EF being energized on the first relapse of dialling relay CF. The control circuit is marked busy when either of these switches is off-normal. At the first step of DH, a starting circuit is closed for magnet DM, which continues stepping by self-interruption until the position marked by DG is reached, when it holds in series with PF, which locks and places the holding circuit under the control of CF. When the final digit has been received, CF falls back and magnet DM steps to the position marked by DH, whereupon QF pulls up and releases magnet DM, advancing the selector one step to the wanted line. Test relay HF is connected through a rectifier RF to wipers DM3, DM4 during the release period of EF and energizes if the wanted line is idle, holding EF, releasing QF and connecting lowresistance battery to wire p to operate JJ, Fig. 5. Switching relay HAF energizes and disconnects common line relay AF to free the control circuit. If the wanted line is busy, EF falls back and connects up busy tone. Completion of connection, Fig. 5. Relay JJ locks and applies ringing current through ring cut-off relay FJ, which energizes upon reply by the called party followed by back-bridge relay DJ. Booster metering battery is applied to wire p pending the relapse of JJ. Upon release, the first and second selectors restore to normal, while the final selector remains in its set position. Specifications 358,293 and 363,129 are referred to.