Patent GB-754855-A (GB)
Title: Selecting system utilizing rotary switches
IPC: H04Q3/00
Filed: 1954-03-19
Abstract: 754,855. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. March 19, 1954 [April 27, 1953], No. 8150/54. Class 40 (4). In a single-motion group selector or final selector employing wiper-switching, the groups of outlets are arranged in staggered formation in two or more sets of contact banks, so that the switch wipers travel less than the length of one group in order to reach the beginning of the next group; circuits for the switch magnet are completed over a common control wiper and bank. The Figures show a group selector in which the odd-numbered groups are arranged in one set of banks and the even-numbered groups in another. A counting chain of relays R210- R395 responds to dial impulses, two relays for each impulse, and a circuit for a wiper-switching relay R170 is alternately prepared and opened by successive impulses. A magnet M180 moves the switch through the requisite number of steps at each impulse by self-interruption in a circuit over a control wiper 182. Detailed operation. A call from a substation 10 is extended through a line circuit, finder and allotter combination 102 and the calling party receives dial tone. Line and hold relays R120 and R130 respectively are operated. When the calling subscriber dials the first digit, reception of the first dial impulse releases line relay R120 to bring up relays R140 and R150, thereby operating the first counting relay R210 which locks up and prepares a circuit for the second counting relay R220. At the end of the impulse R120 re-operates and R150 falls back, bringing up R220 which locks up and prepares a circuit for the third counting relay R230. Similarly R230 and R240 respond to the second dial impulse, and so on along the counting chain R210-R395, a circuit for the wiper-switching relay R170 being alternately prepared and opened by successive impulses. At the third impulse the operation of R250 causes the switch magnet M180, by self-interruption in circuits over the control wiper 182, to step the wipers to the start position of group 3. Similarly the wipers are advanced by subsequent impulses to the corresponding groups of contacts, which are staggered in two banks as shown so that the switch travels less than the length of one group in order to reach the next. At the end of the digit the line relay R120 remains operated, R150 is released and so is slow-releasing relay R140. If the digit is " 1 ", the release of R140 causes the magnet M180 to move the wipers one step to the beginning of group 1 and brings up the wiper-switching relay R170. The switch now hunts over the selected group until wiper 179 encounters an idle outlet, which is marked by absence of earth. This stops the switch and removes a short-circuit from a relay R110 which operates and extends the calling line over the selected idle outlet to the next switching stage, from which earth is returned over wiper 179 to hold R110 after the ensuing release of R120 and R130. If, however, there is no idle outlet in the selected group, the switch steps beyond the last outlet so that wiper 179 engages a contact such as 194, inserting a relay R160 in series with the magnet M180 which is thereby prevented from operating and thus stops the switch. Relay R160 operates and sends busy tone to the calling subscriber, whose hanging up initiates the release of the equipment, a homing circuit for the switch being completed over off-normal contacts 195. Specification 642,586 is referred to.