Patent GB-140367-A (GB)
Abstract: 140,367. Automatic Telephone Manufacturing Co., (Assignees of Jacobsen, E.). March 13, 1919, [Convention date]. Automatic and semi-automatic exchange systems.-A numerical switch adapted to select an idle line from a selected group comprising a large number of lines (e.g. several levels) is provided with discriminating-means whereby, when all the lines are busy, if the switch had been seized by an operator, it remains stationary until one of the lines becomes free, whereas if it has been seized by a subscriber, it rotates to test the lines in turn. The switch is provided with two auxiliary sets of contacts; one set of contacts 16, Figs. 1 and 2, comprises one contact for each row, is engaged by a vertical wiper 15, and indicates whether or not the lines of the corresponding row are all busy; the second set of contacts 21, 22 has one contact corresponding to each line and is engaged by a chain wiper 18, which, when all the lines are in use, extends the ground connexion on the contact 21 to a contact 22 connected to a relay 23, 40, 41. Thus, when all the lines in either of the two lower rows are busy, the relay 23 or 40 is energized and earths the corresponding contact 16 through a resistance 39, whereas when all the lines in all three levels are busy, the relays 23, 40, 41 are all energized and the contacts 16 of the two lower rows are earthed directly. The relays 62, 67, Fig. 1, are only energized when the switch is taken into use by an operator over terminals 63 - - 66, Fig. 1. Operation of switch H, Fig. 1, by ordinary subscriber. When the subscriber A removes his receiver, his line is connected in known manner by switch C to an idle switch H, the line and release relays 5, 6 being energized. The first set of selecting-impulses is repeated by the relay 5 through the series relay 12 to the vertical magnet 7, which raises the wipers to the desired level, which is assumed to be the lowest level of the group of three levels shown in Fig. 2. On the first vertical movement, the relay 24 is energized over the off-normal contact 30, locks up, and prepares the circuit of the rotary magnet 34, which, if there is an idle trunk in this level, is energized as soon as the series relay 12 releases at the end of the selecting-impulses. The rotary magnet 34 and the relay 12 interrupt the circuit of each other alternately until the idle line is found, whereupon the relay 47 energizes and completes a circuit for the. ringing-generator R through the called line and the upper winding of the ringing-cut-off relay 60, which is energized when the called subscriber replies and completes the talking circuit. If, however, all the trunks in the first level are in use but there is an idle trunk in the second or third level, the contact 16 engaged by wiper 15 will be earthed through a resistance 39, Fig. 2, so that relay 37 (but not relay 36) will be energized, opening at contact 42 the circuit of the rotary magnet 34, and closing at contact 44 a further circuit for the vertical magnet 7, which raises the wipers to the next level. If this contains no idle line, the relay 37 is again energized and the magnet 7 moves the wipers to the next level. If all the trunks in all three levels are in use, the contacts 16 of the two lower levels will be directly earthed, so that both relays 36, 37 will be energized; but the energization of relay 36 is without effect when the switch is controlled by a subscriber, since the springs 14 are shunted by the springs 38 of relay 67. The wipers are therefore raised to the third level as before, and are then rotated past all the busy trunks, a busy signal being given to the calling-subscriber by the closure of contact 46. Operation of switch H by operator through toll selector E, Fig. 3. The selector E is operated by the line relay 76 and vertical and rotary magnets 77, 78 to seize the selector H, Fig. 1, over terminals 63 - - 66, Fig. 1. The relay 79, Fig. 3, connects the back-bridge relay 98 across the talking circuit, closes a circuit over wiper 85 and terminal 63 for the relays 67, 5, Fig. 1, and over wiper 70 and terminal 64 for the relay 62. The next set of impulses is repeated by relays 76, Fig. 3, and 5, Fig. 1, to the vertical magnet 7, which raises the wipers to the desired level which is again assumed to be the lowest level shown in Fig. 2. If there is an idle line in the first or other level, the switch operates as before, and the connexion is extended to this line from the operator's position over the contacts of relays 62, 67. When the operator presses her ringing-key, relay 90, Fig. 3, energizes relay 91, which locks up and opens the circuit over wiper 70 for relay 62, which de-energizes and connects the ringing- generator R to the called line, this circuit including the slow-acting relay 96, Fig. 3, which is energized when the subscriber replies and opens the locking-circuit of relay 91, thereby re-energizing relay 62, Fig. 1. The back-bridge relay 98, Fig. 3, is then energized over the called line and controls a supervisory signal at the operator's position. If, however, all the lines in all three levels are in use, relays 36, 37 are both energized as before; but, as the relay 67 is also energized (as the call is from an operator's position), the circuit of the vertical magnet 7 is now closed only through a resistance 86, which prevents its operation. The switch therefore remains with its wipers opposite the lowest level of terminals, and a busy signal is sent over contact 100 of relay 36 to the operator, who, instead of releasing the connexion, may leave it set up until a line becomes free. When this occurs, the relay 36 or both the relays 36, 37 de-energize, short-circuiting the resistance 86, so that the switch operates as before to select the idle line.