Patent GB-426790-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone or like exchange systems
IPC: H04Q3/00
Filed: 1933-10-06
Abstract: 426,790. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, E. P. G., HARTLEY, G. C., and REYNOLDS, W. J., 63, Aldwych, London. Oct. 6, 1933, No. 27591. [Class 40 (iv)] In a rural office, a discriminating switch is adapted to prevent the establishment of connections to exchanges having any desired combination of from one to four digits. Such prevention may apply to all subscribers or only to particular ones, e.g. coin-box subscribers. The same switch also controls zone-metering and in any one position may prevent the establishment of connections to the corresponding exchange by coin-box subscribers and the transmission of metering impulses for calls to that exchange by other subscribers. Means may be provided for preventing incoming calls from being further extended to other exchanges in the network. Calls to the automatic equipment and the manual board at a main exchange are extended over the same group of junctions by dialling 9 and 0 respectively. Local call. Ground on lead STL when a call is made operates relay ST which completes a circuit for finder magnet FM. When the calling line is reached, relay P operates over wiper fm3 and locks over its right-hand winding in series with LH which operates DC. Relay AS operates over the loop energizing B which releases ST, P. The impulses of the first digit (2 for a local call) are repeated to magnet DM and when series relay C releases at the end of the digit, relay L operates over wiper dml, locks over its lower winding, and advances switch D to contact 11. The second digit also passes to magnet DM and during its reception relay E operates and connects up magnet SM to advance switch S to the beginning of the group marked over wiper sm9, jumpering LMC, and wiper dm2. At the end of the digit, relay ST operates to direct the third digit to magnet SM and if the second digit was even, wiper-switching relay J is energized over wiper dm1. At the end of the third digit DC releases and relays JM, MD operate. If the wanted line is idle, relay P operates over its left-hand winding and locks in series with H which connects up ringing-current and releases P. When the called subscriber replies, relay FS operates and extends the called loop back to relays DS, IS. Call to P.B.X.. subscriber. P.B.X. lines are are connected to the odd bank of switch S, and contacts in bank sm8 corresponding to singleline subscribers and last lines of a P.B.X. group are multipled to ground over contacts h8, lh6, to maintain relay M operated. If the first line of a P.B.X. group is called and is busy, the release of M completes a driving circuit for magnet SM and this circuit is maintained until P operates on an idle line or M on the last line of the group. In the latter case G operates to give a busy signal. Call to manual board at main exchange; indicating class (coin-box) of calling subscriber operator - hold and recall provisions. In response to digit 0, relay O operates over wiper dml and causes E to energize to complete a driving circuit for magnet SM. Hunting occurs as in the previous paragraph, but ringing is suppressed by the immediate operation of relay FS over its right-hand winding. For a call from a coin-box subscriber, relay CB operates over wiper fm5 and causes high resistance to be inserted in the b-wire to give a characteristic signal to the operator. Contacts dr3, o6 hold relay B independently of the calling subscriber. If the operator wishes to recall the calling party, the application of ringing-current to the b-wire energizes RR which connects the local ringing source to the calling loop. When the subscriber again takes down his receiver, the operation of AS, IS releases RR. If all junctions are busy when a call is made, means may be provided, in the manner described in Specification 426,865, for recalling the subscriber when a junction becomes free. Call to automatic equipment at main exchange. In response to digit 9 the call is extended over an idle junction as in the previous paragraph, the ninth and tenth contacts in the bank of dm2 being multipled, but since relay AU is operated over wiper dm1, relays DS, IS are bridged across the outgoing loop to give a different calling signal. Further digits are repeated over this loop and when the called subscriber replies, relay DS operates, being no longer effectively shunted by rectifier WRB, and repeats back the reversal. Call to adjacent exchange. Digits 6 and 8 correspond to adjacent automatic exchanges and digit 7 to an adjacent manual exchange. Wirings from terminals in banks dm1, dm2 cause such calls to be extended in the manner already described, relay AU operating in the former case and relay O in the latter. Incoming call; trunk-offering. Incoming junctions are connected to the banks of finders F so that incoming calls are extended as for local calls. If the wanted subscriber is busy, relay G energizes giving busy tone and connecting relay RR to the b-wire so that the application of ringing-current to this wire by the distant operator energizes RR which in turn energizes DR, TK. The latter completes a talking circuit through the link and if the local connection is released, relay G releases. Further application of ringing-current again energizes RR, causing the operation of H, the release of TK and the application of local ringing-current through FS. Preventing incoming calls from being further extended. To prevent subscribers who would be metered for a call to a second exchange from dialling further digits and so extending the call to a further exchange, the terminals of incoming junctions in bank fm5 are connected to relay BO which operates so that if a further digit corresponding to an outgoing junction is dialled, relay NU is operated over wiper dm1. Metering. When relay DS operates on the reply of the called party, relay JM is shortcircuited and one or more metering impulses are transmitted over wiper fm6. For a local call, a single impulse is transmitted from SFS over contacts o10 and au10. For calls to an adjacent exchange, switch D is on its 6th, 7th or 8th contacts and an appropriate number of impulses is transmitted from one of the leads MPC over a jumper to the corresponding contact in bank dm5 and then over the wiper and contacts y1, au10. At the end of the cycle, ground on lead FP short-circuits MD to open the circuit to wiper fm6. For calls to the mainexchange manual board (digit 0) no automatic metering occurs the tenth contact of dm5 being disconnected. For calls to or through the main-exchange automatic equipment (first digit 9), metering may be in accordance with the first 2, 3 or 4 digits. After the first digit relay L operates over wiper dm5 moving switch D to its 11th contacts from which it is further set by the 2nd digit. If this digit is 1 to 7 or 0, metering is controlled by a jumper from the corresponding contact to MPC. If the second digit is 8, relay Z operates, re-energizing L which restores D to normal and the switch is then set by the third digit and metering is determined by jumperings to the first part of bank dm5. If the second digit is 9, relays Y, L operate, the switch D is set by the third digit and if this is other than 8 metering is in accordance with jumperings to the first half of bank dm4. If the third digit is 8, relay L operates again, switch D responds to the 4th digit and metering is determined by jumperings to the second half of bank dm4. If multi-metering is not provided, the dotted connections are replaced by the x connections. Restricted service. Coin - box subscribers may be prevented from making calls to the main-exchange automatic equipment by wiring the 9th contact in bank dml to contact cb5 so that when CB is operated relay NU operates and gives NU tone. Alternatively, it may be arranged that, when a coin-box subscriber dials 9, relay O is operated so that the call is extended to the operator's board. Calls to adjacent exchanges may similarly be barred to coin-box subscribers by jumperings to contact cb7. Arrangements may also be made so that any exchange code of 1, 2, 3 or 4 digits may be barred either to coin-box subscribers only or to all subscribers. This is effected by jumperings from banks dm4, dm5 to the terminal set SFS in a manner similar to that employed for metering in accordance with different numbers of digits, the jumpers being to the lowest terminal (directly connected to relay NU) if a particular code is barred to all subscribers and to one of the terminals connected to armatures cb1-cb4 for codes barred only to coin-box subscribers. Digit absorption. A first digit 5 may be absorbed by connecting the fifth contact of dml to relay W which, when operated, completes a restoring circuit for switch D over bank dm3. Extension to 200 subscribers. A second similar board may be added characterized by a first digit 3. In this case, relay AU would be strapped to the 3rd contact of dm1 so that selection of a tie-line to the second board takes place as described for an outgoing call. In the second board, relay LL operates over bank fm5 energizing L which steps the switch D to its 11th position in preparation for receiving the 2nd and 3rd digits. With 3-wire tie-lines, the feed in the first of the two links in series may be cut out.