Patent GB-180331-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone systems
IPC: H04Q3/00
Filed: 1922-05-18
Abstract: 180,331. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Wicks, J.). May 23, 1921, [Convention date]. Automatic exchange systems.-In a connector in which the test relay is connected to the test wiper over the front make-before-break contacts of a slow-release relay energized throughout the transmission of the final set of impulses, it may happen that this slow relay de-energizes before the wipers are properly centred, in which case the test relay does not energize and the busy signal is not given. In order to increase the time during which the test relay is connected to the test wiper, two slow-release relays are employed, one of which is energized in series with the rotary magnet and closes the circuit of the second, whilst the test relay is connected over make-before-break front contacts of the second, and, upon energization, prepares a looking circuit for itself which is completed over back contacts of the second slow-release relay when the latter de-energizes. The invention is described with reference to a rotary connector H which has access to a bank of terminals in which groups of lines have the same numerical significance and in which, in the event of the first line of a group being busy, the switch automatically hunts over the remaining terminals of the group in search of an idle line. When the connector is taken into use, relay 401 energizes and the tens impulses are repeated to the vertical magnet 413 in series with the relay 404 in the usual manner. At the end of the set of impulses, relay 404 de-energizes and the units impulses are repeated to the rotary magnet 412 over a circuit 424, 429, 438, 435, 447, 407, 460, during which slow-release relay 407 remains energized and completes the circuit of a second slow-release relay 408 which connects the test wiper 472 to the test relay 406. Shortly after the end of the units impulses, relay 407 falls back, but relay 408 remains energized a moment longer, maintaining the connection of the test relay to the test wiper until after the wipers are properly centred. If the called line is busy and is an ordinary individual line, the test relay 406 energizes, locks up and connects the busy-tone generator T' to the calling subscriber's line. If, however, the line seized is the first of a group, the connector hunts automatically and the busy signal is only sent if all the lines of the group are busy. All the lines in a group, except the last line, have their two test terminals 475, 476 strapped together, so that, in the case of a busy line, both are connected to earth. Upon the energization of the test relay 406 due to the first line of the group being busy, stepping relay 403 energizes in a circuit 464, 445, 471 and locks up, completing a circuit for the rotary magnet 412 which rotates the wipers on to the next set of contacts and breaks the locking circuit of the relay 403. If the next line is busy relay 403 locks up again and the switch is automatically stepped forward until an idle line or the last line of the group is reached. During the stepping movement, relay 408 energizes in parallel with the rotary magnet and disconnects the busy tone machine T<1>. If the last line of the group is found to be busy, relay 403 does not again energize, relay 408 relapses and the busy signal is given. When an idle line is found, switching relay 409 energizes in a circuit 428, 446, 409, 454, 472, 482 in series with the called subscriber's cut-off relay 480, and connects the ringing generator V to the called line. When the called subscriber A<1> replies, ringing cut-off relay 405 energizes to complete the talking connection. If both subscribers hang up, relays 400. 401. 402 de-energize to complete a circuit for release magnet 410 and to control the release of the preceding switches. If the calling subscriber hangs up first, relay 401 relapses and in the interval of time before relay 402 relapses an impulse is sent to relay 408 over a circuit 407, 435, 429. Relay 408 momentarily disconnects earth from the test conductor c to start the release of the preceding switches and then restores the earth connection to prevent the connector frcm being marked idle. The connector is released when the called subscriber hangs up. If the called subscriber hangs up first, relay 400 falls back, but the connector is not released until the calling subscriber hangs up, the connector thus being in all cases released by the last party to hang up.