Patent GB-314563-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1928-03-29
Abstract: 314,563. Standard Telephones & Cables, Ltd., Baker, J. H. E., Cameron, A. H., and Haigh, In. B. March 29, 1928. Semi-automatic exchange systems .-In a system in which a connection between subscribers at one exchange is set up by automatic switches controlled by an operator at a distant exchange, and in which the talking circuit does not include the junction to the operator, the talking circuit is independent of any switches by which access to the junction is obtained and also of the numerical switches by which the operator set up the connection. In the system described, a subscriber such as 21, Fig. 5, is connected over a finder switch LF to a junction leading to the distant operator who, by the act of plugging in, associates 'a common register-marker RE, SW with the junction in use. The marker comprises a twodigit single motion switch and, after being set by the operator on to contacts of the wanted subscriber's line, for example 28, takes into use an idle link circuit LC comprising a pair of switches LCF, LCC which hunt for the calling and wanted lines respectively. The finder LF and registermarker are then released. The switches of the link-circuit are controlled by common relays in the marker. The operator is prevented from overhearing a conversation over a connection set up by her except by setting up a fresh connection to one of the parties; she may offer a call to a busy subscriber. For incoming calls, the operator sets the marking switch and an idle finder LF is started up and acts as a forwardly hunting switch to find the marked contacts of the wanted line. Connection to main exchange. Belay L operated by calling subscriber's magneto MO locks up in series with common start relay 15, Fig. 4, which completes a circuit 2(2), 15 (1), 3(2), BK, K(1), B(3)] for relay S, Fig. 2. Magnet DM of call finder LF is operated from ground at S(1) and steps LF until test relay H(i) energizes in series with the non-inductive winding (iii) of L and relay 15, the winding (ii) of L being of high resistance. Relay H directly grounds the test terminal, locks up over K(4), S(3), and energizes B which at B(3) transfers the starting circuit to the next idle finder. Relay L falls back as it is short-circuited at H3, and is followed by 15. Relay B releases S and connects ground from B (1) over A to the negative wire of the junction to operate relay Y, Fig. 3, A remaining inoperative. Lamp CL lights up. Communication with calling subscriber. When the operator plugs into jack T, relay CA pulls up, extinguishes CL, and connects battery over Z to the positive wire to operate Q, Fig. 2, R remaining unoperated. The operator converses with calling subscriber if his receiver is off the hook. If not, relay C operates over R (2), the negative wire, and subscriber's bell, and releases Y which lights CL to inform operator that the subscriber must be rung. The operator inserts plug RP into jack O and throws RK to operate relay D which connects jack O to the junction so that ringing current passes over the negative wire. Battery over RA and the positive wire operates relay R which at R (1) short-circuits line relay L (i) so that a mid-point grounded bell, indicated by dotted lines in Fig. 1, may be rung over both wires. When key RK is restored and the subscriber has lifted his receiver, relays D, R, and C falls back and relay Y pulls up to break the circuit of lamp CL. Local call; operation of marking switch SW. The operator inserts plug OP into jack O and relay D connects battery over relay M and the positive wire to operate Q but not R. Relay A now pulls up over B (i), C (i), the dial springs, and impedance N, and closes a circuit [RB, Fig. 4, A (2), 9 (5), H] for impulse relay 1 which energizes 2. Relay K, Fig. 2, pulls up over 2 (2), locks over K (2), and connects the junction to marking switch SW. Ground from 6 (2), Fig. 4, is connected over K (4) to hold H, and also over H (6), E (3) to relay 16, Fig. 4, which locks to ground at 2 (3), while at K (1) the starting circuit is transferred to the next junction independently of relay B. Relay 1 responding to the dialled impulses completes the circuit [1 (2), 2 (1), 5 (1), 10 (1), 6 (1)] for magnet SWM of switch SW relay 3 being operated during an impulse train. This switch is a 25- point rotary switch, the subscribers being numbered 20 to 39 and 41 to 45. If the first digit is 2, SW steps on to contact 45 and, when 3 relapses, relay 8 pulls up over 8 (4), 45, 3 (3), 6 (6), 2 (3), and locks. If the first digit is 3, SW steps on to contact 21 and relay 13 energizes and locks when 3 falls back. A self-interrupting circuit is now completed for magnet SWM which steps SW on to contact 20 where relay 8 pulls up and opens the circuit. If the first digit is 4, SW steps to 22 and relay 14 pulls up to complete the self-interrupting circuit for SWM and SW steps on to 30 where relay 8 pulls up and stops the movement. Switch SW is now standing on contacts 45, 20, 30 according to the digit dialled. Relay 1 responds to the second train of impulses and steps SW as before but relay 4 now pulls in addition to 3. At the end of the train and in the interval between the release of 3 and 4, relay 11 operates over 4 (3), 5 (2), 3 (4) and is followed by 10 over 11 (4), 2 (3). Relay 10 connects ground from 10 (4) over relay 9 and the positive wire of the junction to operate M, Fig. 3, which lights SL to indicate successful dialling.. When relay 4 falls back relay 11 is connected to the test wiper T and, if the wanted subscriber is free, falls back to release 10 and extinguish lamp SL. There is no speaking connection between the operator and wanted subscriber in this case. Selection of local connecting link; ringing. Relay 16, which operates when switch SW is taken into use, prepares circuits leading to a link such as LCF, LCC. As described, two such links are provided, and if that shown is busy, relay 7 operates over 16 (7), 1 (3), COK, HC (1), Fig. 1, and locks up over 2 (3). The leads from the second link are connected up over front contacts of 7. In the second link, the connection of HO (1) indicated at X is replaced by that shown in dotted lines, so that if it is also busy, relay 5, Fig. 4, pulls up and causes a tone signal to be sent to the operator as will be described later. The second link is given preference if COK is thrown since 7 now operates over HC (1) (back). The release of 11, in the case of a free subscriber, opens the circuit of slow-to-release relay 10, but in the meantime, 6 operates over 11 (2), 10 (5), 2 (3), locks up, opens the circuit of magnet SWM and releases 8 together with 13 or 14 if operated. Relay 10 is now connected over 6 (4), 9 (4), 11(1), the negative wire and subscribers bell, and operator throws RK to ring the line. Battery over relay M and the positive wire operates 9 which removes 10 from the negative wire but holds this relay over 2 (3). Relay 9 completes the ringing circuit over the negative wire at 9 (1) and loops the wires over 9 (3), 11 (1), so that a mid-point-grounded bell may be rung over both wires.. Relay 1 is removed from the junction but is held over RB. Completion of conversation circuit. Relay 6, operated as described in the preceding paragraph, completes the circuit of magnet LCFM of finder LCF which hunts for the calling line marked by ground from 6 (3) over 16 (3), K (5). and wiper C of LF. When the calling line is found, 18 operates over wiper C of LCF. locks up, and at 18 (1) changes over to magnet LCCM of LCC which hunts for the called line marked by battery over wiper O of SW. When LCC reaches the marked contacts, 17 pulls up and locks. On reply of the called subscriber, relay 10, which has been held over his bell, falls back, and HC, Fig. 1, pulls up over 7 (2), 16 (1), 10 (2), 17 (2), 6 (2) switches the connection through. connects battery feed over CC and PC to both wires and locks up. Release of junction and temporary used switches. Relay 10, on falling back, releases H, Fig. 2, and at 10 (4) removes ground from the positive wire of the junction so that relays 9 and M fall back and SL is extinguished. The operator withdraws plug OP and D releases but Y operates in series with the impulse relay 1 and keeps CL alight. Relay 1 releases, as it cannot remain operated in series with Y. and is followed by 2 and K. Relay Q now pulls up followed by B and when the operator removes the plug from T, relays Q, B, Y fall back and CL is extinguished. Relays 18, 16, 6 are released by 2 and 17 follows 6. The homing circuit for switch SW is now completed and relay 3 operates in a parallel circuit to hold open the starting circuit at 3 (2). Release of connection. The link LCF, LCC releases when either party hangs up since CC operates over the bell and short circuits HC which releases CC. Switches LCF, LCC have no normal position. Release on abandonment of call. If the calling subscriber does not reply when the operator plugs in, and the subscriber bas replaced his receiver, relav C is operated and lamp CL is not extinguished. The operator removes the plugs from jacks T and O, and relay Q relapses followed by relay C. In the interval, B releases and is followed by H. If the subscriber has not replaced his receiver, relay U does not operate and the operator removes the plug from T but inserts RP into O. She throws key RK or OK to operate relays D and Q. Relays R and C pull up and when the key is restored release takes place as before. Wanted subscriber busy; operator offers call. Relay 11 remains operated when connected to the test wiper of switch SW. A self interrupting circuit is now completed for relay 12 in series with relay 1 (ii), and tone induced in 1 (i) is transmitted to the operator. The operator may offer the call by throwing key OK so that battery over the lower winding of M is connected to relay 9 which operates and, in conjunction with 11, completes a conversational connection between the operator and wanted subscriber