Patent GB-622268-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04Q3/00
Filed: 1947-01-01
Abstract: 622,268. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., PEARCE, O. A., and JONES, E. W. Jan. 1, 1947, No. 7. [Class 40 (iv)] In a system in which an appropriate number of finder switches are caused to hunt depending on the energization or non-energization of a relay in a bridge circuit as described in Specification 489,107, an auxiliary energizing circuit is momentarily completed for the relay when a line calls to ensure proper operation of the relay. Primary finders. As long as primary and secondary finders are available, relays FB, FBS, Fig. 5, are energized so that initiation of a call on the line SL, Fig. 3, operates the line relay L to operate the related motor switch relay MS in the sequence marking equipment SME to cause a motor to rotate a series of cams. The line relay also marks the appropriate contact in the bank of primary wiper PF4 and disturbs a bridge circuit comprising the resistances YB, YC of all calling lines, resistances YF, YG of all primary finders in use, rectifier MRJ and start relay S, whereby if the number of calling lines exceeds the number of primary finders in use, the start relay S pulls up. To ensure the operation of relay S if the bridge is nearly balanced, cam-operated contacts PSC close momentarily to short-circuit the resistances YB. Operation of the start relay S extends earth to the sequentially-operated cam contacts PMC1-8, and the first of these contacts to close energizes relay FS over its corresponding lead 63 or 32-38, and energizes relay VS through a related rectifier MRAMRH. Relay FS energizes a self-interrupting primary finder driving magnet PFM, Fig. 3, so that the wipers hunt for the calling line. Relay FS also connects the resistances YF, YG of the allotted primary finder into the bridge circuit, which balances to release the start relay S so as to prevent the marking of further primary finders. Relay FS also operates the start relay SS in the secondary control circuit, Fig. 5. The operation of relay VS energizes a vibratory relay VB, which energizes a relay SR to release relay VS. The vibratory relay VB therefore relapses, but the vibration of its contact spring maintains relay SR for some time during which the primary finder will normally find the calling line, whereupon a low resistance test relay FT pulls up to halt the finder and to mark the appropriate contact in the bank of wiper SF1 of the secondary finder. If the primary finder fails to connect with the calling line before relay SR falls back, relay FS releases to permit re-operation of the start relay S to allocate another finder. Secondary finders. Operation of the secondary start relay SS over contacts FS7, 8 seizes a pair of link selectors FLS, Fig. 5, and another, not shown, to start the pair of associated secondary finders ASF hunting in a manner similar to the operation of the primary finders. Relay LS in each link selector is equivalent to relay FS in the primary finder in adding resistances YR, YS to a bridge circuit to release the secondary start relay SS to prevent starting up further secondary finders. When one of the finders encounters the appropriate primary finder, relay FTA operates to halt the wipers and energize relays KA, SW. If no other primary finder is marked, the other secondary finder of the pair taken into use continues to step until relay LS releases at the release of relay SRS. The energization of relays SW, KA operates relay K in the calling line circuit, extends the speaking conductors to the battery feed relay A in the link circuit to transmit dial tone to the calling subscriber, releases relay FS and prepares to route any subsequent marking from the related contact PMC to another primary finder in the group, and disconnects the appropriate lead to relays FB, FBS, which de-energizes, however, only if all the primary and secondary finders, respectively, are busy. Relay KA releases relay LS and also extends the lead 81 in the secondary control circuit to the lead 77 in a subsequent link circuit. Operation of relay K, Fig. 3, releases the line relay L which de-energizes the corresponding winding of the motor switch relay MS to stop the cams if none of the other groups are dealing with calls. Contacts L2 disconnect battery from bank PF4, and if the subscriber is privileged, substitutes an earth condition. Defects. If contacts SI fail to close after the start of a call, a slow-acting flood start relay FF pulls up to start all the free primary finders hunting, the relay FF releasing at the operation of relay VS. A similar relay FFS operates if contacts SS1 fail to close. Crowded conditions. If the primary finder corresponding to the first of the cam-controlled contacts PMC1-8 closed is already engaged, earth is extended over the related test jack TJ1-4 and contacts SW3 to mark the first free finder in the group. Similarly, if either or both of a pair of link selectors are busy, a marking over lead 81 is extended over the operated contacts KA5 of the operated link selector to the next link selector, so as to operate two link selectors each time the start relay is operated. If all the primary finders of a group are busy, relay FB releases to prevent operation of start relay S or flood start relay FF and connects busy tone at transformer TRA to all subsequent calling lines. Relay FBS acts similarly for the secondary finders.