Patent GB-191303339-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1913-02-08
Granted: 1914-02-09
Abstract: 3339. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Feb. 8. Automatic exchange systems. -Relates to automatic private branch exchange systems in which several trunks are used to connect the branch exchange with the main exchange. These trunks terminate at the branch exchange in selectors or connectors of ordinary type and at the main exchange in the terminals of a set of so-called " rotary selectors," in which two or more groups of trunk lines terminate in the same level. The rotary selectors operate somewhat like rotary connectors, that is to say after the wipers have been raised to any level, they do not begin to rotate automatically, but in response to the impulses for the second digit, they are rotated on to the contacts corresponding to that digit. If the first of the group of contacts corresponding to this digit is busy, the wipers rotate automatically to find an idle contact, or, if all the trunks are busy, until they reach the last contact of the group, when the selector is arrested, without, however, making connexion with the trunk. The rotary selector is provided with two test wipers, and two sets of private bank contacts, the last pair of contacts for each group of trunks being connected together as shown at 82, 83, Fig. 2. The rotary selectors are adapted to repeat the sets of impulses for operating the connectors at the branch exchanges. An arm on the impulse wheel short-circuits the receiver and transmitter during the transmission of the selecting- impulses. Live switch and first selector. A calling subscriber is connected by a line switch and first selector operating in the manner described in Specification 1419/10 to an idle rotary selector F having access to the private branch exchange required. Rotary selector. The line relay 62 is energized over the springs of a reversing relay 67 and the calling station, and closes the circuit of the usual slow-release relay 112. Assuming that the number of the wanted line is 155-20, 155 being the branch exchange number and 20 the local number, the five tens impulses are repeated by the relay 62 through the privatemagnet relay 120 to the vertical magnet 121, after which the private magnet 124 moves the side-switch into its second position in the usual way. The five units impulses are then repeated through the relay 120 and a contact 126 to the rotary magnet 125, which rotates the wipers to the terminals of the first trunk leading to the branch exchange numbered 155. If this trunk is idle, the private magnet 124 moves the sideswitch into its third position, extending the connexion. If the trunk is engaged, its test terminal 61 is earthed, and a circuit is completed over arm 129 and relay 127, which keeps the private magnet energized, thus locking the side-switch in its second position. As soon as the private-magnet relay 120 has fully deenergized, a fresh circuit is completed for the rotary magnet 125 over contacts 126, 132, 131, and 123. The rotary magnet moves the selector round one step and closes a contact 133, thus energizing a relay 134, which controls the contact 132 in the circuit of the rotary magnet. The selector is thus rotated, the rotary magnet and the relay 134 energizing alternately, as long as the relay 127 remains energized, that is as long as a busy trunk is found. As soon as an idle trunk is reached, the relay 127 open-circuits the private magnet 124, which moves the sideswitch into its third position. If the last trunk is also in use, a circuit is completed through the arm 138, relay 137, contacts 136, 135, 234, wiper 60, contacts 82, 83 to ground, the last pair of test contacts being connected. The relay 137 (1) locks up over contacts 135, 142, 157, (2) disconnects the rotary magnet 125 at contact 123, and (3) connects the busy generator M' over contact 143 to the calling line. The private magnet remains energized, so that no connexion is made with the trunk. The selectors are released when the calling subscriber hangs up. When connexion is made with an idle trunk line, and the side-switch reaches its third position, its arm 147 bridges an inductance 151 and a coil 69 of the relay 67 across the trunk 145, 146, thereby energizing the line relay of the connector at the private branch exchange. The line relay 62 controls a contact 152 in this bridging circuit, and thus serves to repeat the final sets of selecting-impulses to the connector, which operates substantially in the manner described in Specification 1298/10. During this repetition of impulses, a slow-release relay 166 energizes in series with the private magnet relay 120, and short-circuits the winding 69 and inductance 151, thus removing their resistance from the trunk circuit. When the called subscriber replies, a relay at the connector reverses, in known manner, the connexions of the battery and line relay to the trunk 145, 146, thus reversing the current in the winding 69, which now assists, instead of opposing, the winding 68, whereby the relay 67 is energized. This reversal of the battery connexions to the trunk 65, 66 produces no result in the system described, but might be used, in known manner, to register the call, or for supervisory purposes in a semiautomatic system. The connexion is released in the usual way when the calling subscriber hangs up.