Patent GB-612896-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1946-10-04
Abstract: 612,896. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and LONG, D. P. Oct. 4, 1946, No. 29710. Addition to 583,834. [Class 40 (iv)] In a line finder system, according to the parent Specification, in which the group of lines served by a group of finders is divided into two or more sub-groups, on the initiation of a cell, a free allotter executes a testing operation to determine the relevant sub-group. The present invention comprises improvements whereby, if an allotter finds the required group of line finders congested, further calls arising in that group are prevented from seizing an allotter and an allotter seized by a call in any group is prevented from testing in to a calling condition in a congested group while congestion of the finders serving that group continues. A number of allotters have a common congestion outlet to which connection is made if an allotter fails to find a free line finder, so as to prevent further search, only the first allotter to connect with the congestion outlet being stopped from searching. Each 200-line group is divided into four sub-groups W, X, Y, Z connected to arcs associated with wiper switching relay WS, groups W and X with the back contacts, Y and Z with the front contacts. The line finders are 200-point motor-driven uniselectors having four double-ended wipers, a number of line finders working on a common multiple of 200 subscribers' lines, while the allotters serve 100 line finders in four groups. Normal operation. Initiation of a call energizes line relay L which connects up the appropriate sub-group starting relay W, X, Y or Z to energize the start relays S in all the free allotters serving finders having access to the calling group. Relay S initiates the operation of the relay chain SA ... SG, and prepares circuits for the appropriate test relay TW or TX and the appropriate start cut-off relay CW, CX, CY or CZ over the contacts of the chain relays. Assuming the calling line to be in sub-group W of the first group, relay TW pulls up immediately and energizes the allotter start relay ST in series with relay TS, which disconnects the relay chain SA ... SG before relay SA can operate. Relay CW operates in series with TW which locks up to prevent the operation of any other TW relay and the starting of more than one allotter switch. For a call in sub-group X, relays TX and CX operate with similar effect. For calls in subgroups Y or Z, however, TW or TX in series with CY or CZ, respectively, pull up after relay SA has operated and the resulting energization of TS locks SA. If the call is not in the first group, chain relays SB-SG operate in succession to test the subsequent groups, and when a starting condition is found, the last relay to operate locks, the locking circuits for SC, SE, SG including the preceding relay and SA. . Search for idle line finder. The allotter start relay ST operates shortly after relay TS to energize the allotter magnet AM to start the search for a free line finder in the desired group. Shortly after, relay SM energizes and releases the start relay S, which prevents further operation of the chain relays. Relays SB, SD, SG mark bank 8 of the allotter to limit the search to finders of the appropriate group, the bank contacts being connected to finders of the different groups in rotation. When a free line finder, indicated by battery on wire p, is encountered, the high-speed test relay T operates and switches test auxiliary relay TA into series with the allotter magnet AM to de-energize AM and stop the allotter switch. Search for calling line. Winding I of relay TA locks up and at ta4 connects earth to energize the impulse receiving relay in the first selector. Relay TA also energizes the line finder magnet LM which drives its wipers in search of the calling line, the condition of relay SA determining whether search should be made in sub-groups W and X or in Y and Z. Assuming the calling line is in sub-group W, highspeed test relay P energizes to switch auxiliary relay PA into series with the line finder magnet LM which de-energizes to stop the wipers. If the calling line is in sub-group Y or Z, as relay SA is operated, relay WS also operates to change over the connections to the line finder wipers and relay DP operates to provide an alternative circuit to energize relay P. Relay PA causes operation of switching relay H, which locks to earth returned on the p wire from the selector, and also causes the release of test relay T and allotter start relay ST. Operation in case of congestion. The allotter switches have no normal position and contacts N1 are open only when the wipers are on the first contacts. In passing for the first time the last contacts in the broken line arcs, which are not connected to finders, the allotting switch is not stopped because relays LC and T are not energized, but when the wipers go on to the first contact position in the full line arc, the high-speed relay LC operates to extend earth to the last two contacts in the broken-line arc of wiper 8. If no free line finder in the group marked over wiper 8 is found, the allotter switch is stopped on the penultimate contact by operation of test relay T which energizes the auxiliary test relay TA and then relay C; which energizes a slow-acting relay CN. CN locks up and releases TA, relay C releasing slowly. The group cut-off relay CO determined by the operated relays in the chain SA-SG now operates to disconnect the test-in circuits for relays'TW, TX so that an allotter seized in response to a call from another group shall not test-in to the congested group, and release any sub-group start cut-off relays that may be operated. Contacts co5 open to prevent any allotter of the group being seized needlessly by a call in the congested group, and co7 operates a congestion meter. The relapse of relay C releases test relay T and disconnects the allotter circuit from resistance YA and the battery common to allow other allotting switches to test-in to the penultimate contact. The allotter magnet AM re-energizes to advance its switch to the last contact position where it is stopped by re-energization of test relay T over periodically-closed contacts sp, which open after an interval to release T and re-operate magnet AM, whereupon the allotter makes another search for a free finder in the relevant group. If a free finder is found, relay T operates in the test circuit over wiper 8 and the marked contact; otherwise the allotter is again stopped in the last position. Alarm and safety circuits. When an allotter is first taken into use, time pulse relay PS energizes at the receipt of an S pulse and causes another time pulse relay PZ to operate at the receipt of a Z pulse, if PS has not released meanwhile, to cause energization of winding I of relay PA, lighting of lamp SL, operation of an alarm relay and release of test relay TW or TX, as the case may be. If relay CN has not operated, release of the allotter is initiated by short-circuiting relays TS and ST, but PZ remains locked and the allotter is locked out until relay PZ is released manually by key DK. If relay CN has operated, ST is short-circuited to release relay SM which releases PZ and CN. So, in the case of congestion, the allotter is not locked out of use, but after the release of relay PZ is free to be seized again by any call in any group. An alarm relay MA in series with the allotter magnet AM controls a delay alarm in known manner. If relay ST releases during the search for a calling line, the line finder switch stops when it reaches the first contacts in the bank. Testing.. For testing purposes, an artificial call may be set up by bridging the middle and one of the outer springs of a test jack RTK to operate relay WX in series with W or X, or relay YZ in series with Y or Z, the first position in the relevant sub-group being marked in the finder banks. When the test-line is found, relays P, PA operate to release WX or YZ and hold relay PA in series with a relay CL common to the all otters of a group. When the line finder switching relay H operates, earth on the test wiper PW operates relay RK to light a lamp RTL. If a call is made during testing, relay WX or YZ is released by the appropriate sub-group starting relay. Operation of key RTK2 energizes test relay T in a line finder testing circuit.