Patent GB-191415338-A (GB)
Title: Improvements in or relating to Telephone System.
Filed: 1914-06-26
Granted: 1915-06-28
Abstract: 15,338. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. June 26. Automatic exchange systems.-The circuit of the release magnet of a connector is closed through a resistance when the calling subscriber hangs up, but the release magnet does not operate until the resistance is short-circuited by a back-bridge relay when the called subscriber hangs up. The resistance may form the winding of a relay, which puts a guarding potential on the test terminals of the connector, so as to prevent its seizure before it is released. The pre-selector of the calling subscriber and the group selectors are all released when the calling subscriber hangs up. The operations in effect ing a connexion between two subscribers on different exchanges are as follows. Preliminary selector. The subscriber's preliminary selector is of the type in which the wipers remain on the terminals of the trunk last used. When a subscriber A removes his receiver, his line relay 43 is energized over the contacts of the cut-off relay 42, and closes a contact 51 in the circuit of this relay. If the wipers 52, 53, 54 are resting on the terminals of an idle trunk, the relay 42 is energized and extends the calling line to that trunk. If, however, the trunk is engaged, the relay 42 is short-circuited over springs 58, 59, 56, 55 and the test lead of the busy trunk, so that the line relay 43 energizes the motor magnet 44. As soon as an idle trunk is found, the short circuit round the relay 42 is removed, and this relay disconnects the line relay 43 and motor magnet 44 and locks up over the test wiper 53. There is a mechanical connexion between the armatures of the line and cut-off relays 43, 42, as described in Specification 12,162/13. Group selector. The group selector E operates substantially in the manner described in Specification 10,376/12 and extends the calling line to the terminals of an idle two-way trunk 98, 99 leading to a connector H at a distant exchange. Trunk connexions. When the trunk 98, 99 is seized, current flows through both windings of a coil 21 and a relay 22 over the calling line. The relay 22 energizes a slow-release relay 25, which grounds the test terminals such as 162, and energizes a second slow-release relay 24, which (1) extends the calling line to the trunk 98, 99 and its line relay 37, Fig. 2, and (2) disconnects from the trunk the leads 113, 114, 161 of the connector associated with the two-way trunk at the calling exchange. The relay 37, Fig. 2, energizes the usual slow-release relay 116, which earths the test terminals, such as 159, of the trunk at the called exchange. Connector. The selection of the, wanted line, the test as to its busy or idle condition, and the supply of ringing-current all take place in known manner. When the called subscriber replies, the back-bridge relays 38, 39 are energized, thereby (1) reversing the connexion of the line relay 37 to the calling line, (2) energizing the ringing cut-off relay 129, and (3) removing a short-circuit around a high-resistance relay 133, which is thus connected in the circuit of the release magnet 36. Release. If the calling subscriber hangs up first, the relays 22, 37, 116 are de-energized. The relay 22, Fig. 1, disconnects relay 25, which (1) removes the holding-ground for the switching-relay 87, whereby the group selector is released, and (2) open-circuits the relay 24, thus restoring the outgoing end of the trunk 98, 99 to its normal condition. The relays 37, 116 complete a circuit for the release magnet 36 in series with the relay 133, the resistance of which prevents the operation of the release magnet, until the called subscriber hangs up, whereupon the back-bridge relay 38 shortcircuits the relay 133 and effects release. The relay 133 marks the connector busy during the interval between the release of the group selector and the release of the connector. If the called subscriber hangs up first, no release is effected until the calling subscriber hangs up.