Patent GB-656190-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: A43B13/32
Filed: 1948-02-20
Abstract: 656,190. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Feb. 20, 1948, No. 5086. Convention date, March 23, 1940. [Class 40 (iv)] . A small cross-bar system includes a number of ringing circuits one of which is seized when a connection to a called party is established. The ringing circuits provide code signals for revertive party-line calls. If the calling station is coin-controlled, the reply of the called party is indicated by a coin tone and the talking circuit is completed when a coin is deposited. Stations are identified by four-figure numbers representing hundreds, tens, units and a code digit. When a call is made to another exchange, a connection is first established over a by-link to a trunk circuit in response to the first digit registered and dialling proceeds over this temporary connection until the normal link circuit is established. The by-link is then released and dialling continues, if necessary, over the new connection. The by-links consist of relay groups, which function both as markers and as switches. Similarly for a call incoming to the exchange, digits are dialled into a recorder over a by-link which is released when the normal circuit is established. An idle recorder and an idle ringing circuit are selected at different stages by a common chain of 10 relays 1802 to 1803 (not shown) in the marker. Idle links and idle junctions are selected by another common chain of 10 relays 1301 to 1303 (not shown). The hold magnets of a line in the call originating and call terminating switches are operated together as described in Specification 656,191. Pulse-correcting relays are included in the trunk circuits. Internal calls. A calling line A is recognized by a common marker M which connects the line through a call originating switch CO to an idle link L and through switches CO, RT to an idle recorder R. Two groups of links are shown. Dialling tone is transmitted and the marker is released. The wanted number is dialled into the recorder and the digits are registered on relay groups. If the hundreds digit indicates that the call is local, the marker is seized again when all four digits have been registered and selects an idle junctor J giving access to the terminating switch CT in which the called line B is located. A secondary switch SS is operated to connect the link to the junctor and the terminating switch CT is operated in accordance with the tens and units digits. If the line is not busy, when tested, an idle ringing circuit RG is seized and is connected to the junctor and to B over a ringing control circuit RC. The marker and the recorder are both released as ringing commences and the ringing circuit is released as B replies. The busy test of the called line is made over contacts of the hold magnet individual to the line in the terminating switch CT. Revertive party-line calls. If the called line is busy, a further test is made for weak battery on the sleeve wire over which the hold magnet in the originating switch C is normally held by ground. Weak battery indicates that the called line is busy with the marker and must therefore be the calling line. The weak battery is sufficient to operate the test relay without releasing the hold magnet. If a line is busy on a connection already completed, the hold magnet in the switch CO is held by ground from the junction or trunk. If the line is busy with a recorder, the recorder provides a holding ground. If, however, the line is busy with a marker, a relay (2300, not shown) in the recorder introduces a resistance between the sleeve wire and ground and the potential of the sleeve is changed to a weak battery potential. The junction is connected to the line through switches CO and SS but is not connected to the same line in the switch CT as the hold magnets individual to the line in both switches CO, CT are already operated when the select magnet in the switch CT is operated after selection of the wanted line. Code signals are provided by means of contacts and cams, one cam for each code, on a common shaft with a generator. The ringing tone supply is interrupted by a relay controlled by cam contacts selected by the ringing circuit and the recorder. The parties are divided between the two legs of the line. Coin stations. Coin stations are allotted special group relays which provide ground to operate a line-splitting relay in the junctor when the ring trip relay operates. The linesplitting relay is released to complete the talking circuit when a coin is inserted at the calling station. The coin inserts a high resistance in the loop to release marginal relays, which control the line-splitting relay. Outgoing call over trunk. If the call is to another exchange accessible over a trunk T, the calling party establishes a connection to a recorder R and to a link L as before and the marker is released. When the first digit, indicating the desired exchange, has been registered, a by-link BL, already assigned for use, is seized directly by the recorder and connects the recorder to a trunk so that digits subsequent to the first are repeated over the trunk. Meanwhile, before all the digits have been registered, the marker is seized again to connect the link L to the trunk. The by-link is released and dialling continues, if necessary, over the link. Selection can proceed at the distant exchange whilst the connection through the link L is being established. The by-links BL function as markers and each includes relays for marking the seized recorder, group relays for connecting a group of trunks to the desired exchange under the control of the recorder, and a relay chain for selecting an idle trunk from the group. Whenever a by-link is seized another is automatically assigned for the next call.  Incoming. call over trunk. An idle recorder is seized through a pre-assigned by-link and dial tone is transmitted over the trunk. The wanted number is dialled into the recorder. The marker is seized as soon as dialling starts and connects an idle link both to the recorder and to the trunk in switch RT. The by-link is released and dialling continues, if necessary, over the link L. The connection through the link and a junctor to the called party is completed as before. Pulse correcting relays. The trunk circuit includes fast and slow operating relays 1407, 1409 (not shown) energized in parallel by the pulse receiving relay. Relay 1407 interrupts the trunk to transmit the pulses. If the pulse received is short, the release period of 1407, less the operating period, is added to the pulse transmitted. If the pulse is long 1409 releases 1407 and limits the period of the pulse transmitted.