Patent GB-268862-A (GB)
Title: Improvements in automatic and semi-automatic telephony
IPC: H04Q3/00
Filed: 1926-01-05
Abstract: 268,862. Standard Telephones & Cables, Ltd., and Wright, E. P. G. Jan. 5, 1926. Automatic exchange systems.-Subscribers in an office 46 take into use on calling a selector repeater, Fig. 1 (Comp.) associated with two hunting switches like that shown in Fig. 2, which seize idle trunks to offices 41, 51. The first digit operates the selector repeater and selectors in the distant offices. Its value expresses a preference for a particular route and if the distant selector on that route finds an outlet the other route is released, but if it is unsuccessful the call proceeds over the other route. One of the two distant offices has the same first digit (4) as the local office and on calls for which the preferred route is via this office, the selector repeater drops back and is reset by the second digit which is also repeated to the distant office. If the second digit denotes a local call, the selector repeater operates like a group selector to find a local line and then releases the outgoing trunk. For convenience in abridging, the hunting switches connected respectively to the terminals U10 - - U15 and U16 - - U21 will be referred to as A and B, and the relavs in the switch B corresponding ta LA, KA will be referred to as LB, KB although the switch B is not shown in the drawings as its circuits are identical with those of the switch A. Selecting trunks to two distant offices. Line relay A, release relay B, and relay F pull up when the switch is seized and dialling tone is sent back from U2. At B.6 a series circuit is completed for relays KA (upper), LA in the switch A and at F.9, ground is connected to U11. Relay LA pulls up and if the trunk on which the wipers are resting is busy, ground from a front contact of its chain relay CH is connected over WS4 to the stepping magnet RS. When an idle line is found the lower winding of relay KA is no longer short circuited and the relay energizes relay CH to mark the trunk busy and switches the leads U14, U15 to the talking wipers W.S.2, W.S.3. When the line switches switch through, the relays XA, XB are energized partially in series with the distant line relays and pull up only their armatures 5, 20 and 6, 15 respectively. If all the outlets of the secondary line switch are busy a chain circuit for relay GB is completed, relay LA is unable to pull up, and relay KA pulls up immediately after relay F to prevent useless hunting. Selecting preferred or idle route. The first digit is repeated at A.8, A.6 to the distant selectors and at A.10 to the magnet V. The parallel relay C short circuits the relays XA, XB during impulsing and shunts relay J (lower) by a resistance RL which prevents the discharge of the talking condensers from affecting this reply. Stepping relay G pulls up on the change-over of springs N and on the relapse of relay C at the end of the digit energizes the rotary magnet R. At the end of the stroke relay G falls back and cannot pull up again because its circuit is opened by relay K. If the preferred route is over switch B (and in this case it cannot be a local call) the wiper W2 now encounters a terminal jumpered to U3 or U6 (U3 being used on the level corresponding to the local second digit). The resistances RB, RS are so chosen that this results only in the energization of relays K, KK. If both the distant selectors have outlets, relays XA, XB will be partially energized and when relay C pulls up at the beginning of the second digit, relay KK is unlocked and relay D pulls up, locks itself and completely energizes relay XB over its upper winding cutting out relay XA. If the selector on the preferred route is unsuccessful it switches through to terminals wired to a high resistance sluggish relay and relay XB falls back. In this case relay XA is energized completely. If the preferred route is over switch A, wiper W2 encounters a terminal jumpered to U4 or U5 which are grounded directly. In this case relay DD and the release magnet Z are able to pull up as well as relays K, KK. When the springs N change back, relay K is released. Relay DD locks up and alters the circuits of relays XA, XB so that when relay D pulls up at the beginning of the second digit, relay XA pulls up in preference to relay B if both distant selectors have outlets. Discriminating between local and distant calls. If the second digit denotes a distant call, wiper W2 on its automatic rotary step encounters a giounded terminal and relay K pulls up. If however the call is local the terminal will be jumpered to U3 or U4 and since relay D is locked up the terminal is dead, relay K is unable to pull up and relay G pulls up again over the test wiper W4 and continues to interact in known manner with the rotary magnet until an idle line is found. Release of unwanted trunks. When relay XA or XB pulls up fully it breaks the loop to the other office and unlocks the corresponding relay KA, KB providing an alternative locking circuit for its own relay KB, KA. Relay LA, LB falls back. In the case of local calls, the operation of switching relay H releases relays A, B unlocking the relay KA, KB to release the distant selectors and the trunk. Completion of connection, metering and release. After the full energization of relay XA, XB, the distant selectors are held by a loop including the retard coil E and the polarized supervisory relay J, except during dialling when the relay C provides a direct bridge and shunts relay J and coil E by the resistance RL. The usual current reversal, when the wanted distant subscriber replies, energizes relay J which applies booster metering battery from U7 to the private wire and releases relay F which after an interval replaces booster battery by ground. When the calling party hangs up relays A, B, D, XA (or XB), fall back releasing the main office trunk and switches and energizing the release magnet. Local calls are metered and supervised from the connector. Busy signalling arrangements. If at the end of the first digit, neither of the selectors finds an outlet and the digit denotes a non-local call, busy tone is sent back from U1 as soon as relay D pulls up at the beginning of the second digit since relays XA, XB are both de-energized. If however the first digit is that of the local office the relapse of relay K breaks the busy tone circuit which is only made if the second digit derotes a non-local call and so causes relay K to pull up again. Exchange attendants' supervisory arrange. ments. When the switching relay KA pulls up, the lamp LP is lit and when the selector is moved off normal the lamp is put out. Relay GB when all the outlets of a group are busy operates an alarm over U22. A delayed alarm on U9 gives a signal if the release magnet fails to function.