Patent GB-319713-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1928-06-27
Abstract: 319,713. Standard Telephones & Cables, Ltd., Baker, J. H. E., Wright, E. P. G., and Cameron, A. H. June 27, 1928. Automatic and semi-automatic exchange systems. - Calls are set up automatically between Strowger offices and offices using singlemotion switches with common control circuits, means being provided such that when a repeater at the Strowger office is seized, the other idle repeaters associated with the same control circuit at the distant office are marked busy temporarily by the seized repeater and subsequently by the control circuit. Means are provided for giving release control to an operator. Single-motion 1st selector, Fig. 2. Relays k, 2 pull up in series over the test wire when the selector is seized; followed by 1, 4, 3. The first digit is repeated by 1 to DM of the marking switch SC which on leaving normal makes 3 dependant on a back contact of 1 and makes a driving circuit for magnet R of the selector. At the end of the digit, 3 falls back, and when the selector reaches the marked group 8 pulls up and makes the test circuit for HA or HB which switches through when an idle repeater is found. 1 and 8 then fall back followed by K and a homing circuit is made for SC. If all repeaters are busy, the selector is stopped on its normal terminals by 8 which pulls up in series with 9 which sends back busy tone. Outgoing repeater at single-motion office, Fig. 3. Line relay A energizes MD which returns holding ground and energizes B which bridges the junction over D, I, takes over release control from MD and locks up. C replaces D, I by a direct bridge during impulsing. Metering and release. When the called party replies D unlocks MD which energizes reversing relay DR to energize the metering relay MR in the calling loop. MR locks to the test wire and short-circuits its line winding. MD is sluggish and is unaffected by momentary irregular operations of D. Release and operator-hold. Release normally occurs when the calling party releases A, B but when a call is made to the operator's position B, Fig. 4, D is not operated and MD therefore remains energized and holds the connection after the relapse of B, being held by I which is reenergized over the upper wire of the junction. When the call is taken down, the relapse of the sleeve relav CO releases I and MD falls and releases the connection. Outgoing repeater at Strowger office, Fig. 6. Line relay 6A energizes 6MD which holds the connection pending the operation of the release relay 6B which is energized over a front contact of 6C at the end of the first impulse and remains locked subsequently over a front contact of 6A. The other repeaters associated with the same control circuit at the distant office are busied initially over 6BÀ1, 6CÀ1 when the repeater is seized, and subsequently by the energization of their relays 60 by the control circuit. 6C short-circuits the inductive bridge during dialling. Incoming selector (single-motion office) Fig. 7. 7K pulls up over the loop to seize the control circuit and locks up. 71 then pulls up over the loop and is followed by 74, 73. 74 over 74. 3 and their normal contacts N grounds the negative wires of all idle junctions associated with the control circuit to mark them busy at the Strowger office. The selector is set in the same way as the first selector described above. Connector, Fig. 8. When the connector is seized, 8K, 82 pull up in series over the test wire and BA pulls up over the loop and energizes 8B. 8A repeats the digits to the tens and units marking switches TC, UC, the sequence being looked after by a series relay 83 which energizes a two-step relay 85 partially at the beginning and fully at the end of the tens digit and a similar relay 87 at the beginning and end of the units digit. 85 energizes 89 which locks up, and makes driving and tens marking circuits for the selector which is stopped at the wanted group by 86. 86 and 87 jointly make driving and units marking circuits for the selector which is stopped on the wanted line by 88 which opens the locking circuit of 89 and connects it to 8H. Busy test, ringing, reply and metering. If the line is idle, switching relay 8H pulls up in series with 89 and locks up short-circuiting the latter which after a short interval connects up ringing current over 8F. When the called party replies 8F releases 8K to free the control circuit and complete the talking circuit and the back bridge relay 8D reverses the connection of 8A to operate 6D in the Strowger office and release 6MD. The latter then energizes reversing relay 6DR to operate the metering relay 5MR in the line. If the subscriber is busy 8H is unable to pull up and the relapse of 89 releases 88 whereupon the selector goes to its last terminals where it is stopped by 88. 8H switches through to a busy tone and 8F pulls up at once and releases 8K to free the control as before. Release. 6A releases 6B and energizes 6C which holds the repeater busy for a short time to allow the single-motion switches to release. 8A releases 8B to free the preceding switches in the single-motion office, but 8D prevents release of the connector and holds the test circuit open until the called party hangs up. If the call is to a manual board, battery is connected to the + wire, D is not energized and MD is not released. The relapse of B energizes C and I is held over the + wire and holds MD to prevent release of the connection. Standstill releases. If the subscriber fails to dial into the 1st selector, Fig. 2, 7, which is connected to the pulse wire TP on the first impulse by a two-step relay 5, responds to the 2nd impulse and causes HA to switch through, releasing the common circuits and lighting PGL. HA remains locked to a key PGK. A similar arrangement is provided by 75, 77 in the incoming selector Fig. 7 except that the initial circuit for 75 goes over a contact of K instead of a contact of 74. This alteration is made because K mav lock indefinitely if accidentally pushed up by hand. The junction is marked busy until the restoration of the incoming selector by ground on - A which holds the distant relay 6C.