Patent GB-516235-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M15/04
Filed: 1938-06-21
Abstract: 516,235. Automatic exchange systems. POLLAK, -J. E. (Associated Telephone & Telegraph Co.). June 21, 1938, No. 18436. [Class 40 (iv)] A mechanical impulse repeater is used to receive the digits of the wanted number and to retransmit them to equipment for automatically recording particulars of connections. The invention is described with reference to a system having a central exchange shown in Fig. 1. All calls initiated at the exchange are extended over a finder 1LF and group selector 1GS with which is associated, over switch AS2, a discriminating register DR, including a mechanical impulse repeater allotted by DDR. The first digit which sets 1GS also operates a discriminating switch and sets the mechanical impulse repeater. If the call is a local one over levels 2, or 3 of 1GS, the discriminating switch and mechanical repeater are restored without retransmission of the digit and the remaining digits extend the call over 2GS, 3GS, FS in normal manner. On a call over levels 1 or 4 to 9 to an exchange in the same zone, the group selector seizes an outgoing repeater OG which associates itself with a tariff determining circuit, RDC including a two-directional switch. In this case, the first digit is retransmitted by the mechanical repeater to the vertical magnet of the switch at RDC but not over the junction, and the second digit which completes the exchange designation is sent to the rotary magnet and over the junction. Both of these digits and also the remaining digits are repeated to the printer PT, for recording the wanted number, and then the tariff digits, as determined by RDC are transmitted to the printer. When this has been done, an allotted identincation repeater IR is taken into use over AS4 and sends 400~ current back over the third wire, whereupon an identification registering and sending circuit IRR allotted by DIRR causes switch AS5 to hunt for the identification finder IF having access to the calling line. The position of AS5 determines the 1000's digit of the calling party and the 200 line group, finders of this capacity being employed. The identification finder determines the tens and units digits and the determination of the 100's digit is completed by the wiper set used. The 10,000's digit is the same for all subscribers on the exchange. The equipment IRR then sends the digits of the calling number in the form of 50# impulses over a simplex circuit over AS5, IF, ILF, IGS to IR which repeats them to the printer PT whereupon the identification equipment is released..On reply of the wanted party, timing equipment at DG sends duration impulses to the'printer. In the cases of special service and interzone calls requiring 3 and 8 digits respectively, the first digit is 0 and discrimination depends on the second digit. In response to the 1st digit, IGS seizes a selector SS and if the 2nd digit is 0 (service call) the discriminator and mechanical repeater at DR which store both digits are restored and the call is dealt with over level 10 of SS. In the case of an inter-zone call over levels 1 to of SS and an outgoing junction the mechanical repeater sends all the digits to the printer but .the first two are not sent over the junction. Other information is then recorded as for a call to an exchange in the same zone. Specifications 458,095 and 505,037 are referred to. Seizure of 1st group selector, Fig. 7, discriminator DS and mechanical repeater MIR, Fig. 11, and response thereof to the 1st digit. When ILF, Fig. 2, finds the calling line, e.g., as described in Specification 376,265, the calling loop is extended over 421, 422 to line relay 505, Fig. 7, of the group selector whereupon 502 pulls up and operates 508 at the distributer DDR, Fig. 8, which completes a self-interrupting circuit for magnet 543 of hunting switch AS2. When the group selector is found, 509 operates and energizes 512, the locking circuit of which includes relay 503 which operates 504 so that 502 is held independently of 505, the calling loop being now extended to relay 513 and the line relay 505 being connected in a loop over wipers 560, 561 of AS2 and the impulse springs 708 of the mechanical repeater. Relay 511 also pulls up to disconnect one of the multiple grounds on the last contact of distributer bank 556 and grounds the contact in this bank on which the wiper is standing so that magnet 542 steps the distributer to the next idle discriminator, 527 being operated during the stepping to prevent interference with busy discriminators. Dial tone is sent from 732, Fig. 11, over relay 513 to the calling line. The first digit is repeated by relay 513 at contact 620 to the line relay 505 of the group selector and to relay 515 which operates 516 during the train and repeats the impulses to magnet 544 of the discriminator DS and to the receiving magnet 545 of the mechanical repeater. Relay 516 operates marking magnet 547 of the mechanical repeater and causes two-step relay 531 to take its first step, this relay being fully operated when 516 relapses at the end of the train. At the group selector, 505 repeats the impulses to vertical magnet 539 and relay 507 in parallel, and when 507, which shortcircuits itself to make it slow, releases at the end of the train, the rotary magnet 540 pulls up over springs VON and S and makes a circuit for 506, 507 in series, 506 being shunted by busy ground but 507 operating and interacting with the magnet until 506 operates on an idle line. Relay 506 locks up in series with 507, performs the usual holding and switching functions and also completes an outgoing loop for impulsing by relay 505 under the control of the mechanical repeater if required. Local calls. When 516, Fig. 10, relapses at the end of the first digit (2 or 3), the marking magnet 547 of the mechanical repeater. is released and 521 operated over wiper 565 of the discriminator switch releases relays 503, 512 with the result that the loop through the group selector is restored and relay 513 which repeats impulses to the discriminator and mechanical repeater is released. Relay 511 also falls back, operates 519, Fig. 10, and releases the discriminator DS. Relay 519 initiates impulse transmission from the mechanical repeater as described in the next paragraph but there is no outgoing circuit for the impulses and the remaining dialled digits pass over the group selector and complete the call in known manner. Calls within the same zone. In this case, relay 520 is operated over the discriminator when 516 relapses after the first digit (1 or 4 to 9). This'relay opens the circuit of the discriminator switch magnet and operates 519, 517, 518 which control the mechanical repeater. Transmitting magnet 546 causes plunger 549 to reset the pin with which it is engaged, and releases 517, 518 followed by the magnet, which withdraws the plunger to allow rotation of the pin disc and operation of the impulse springs 708, the impulses being repeated by relay 505 at the group selector. The mechanical repeater continues to receive and retransmit the dialled digits in known manner but the repeating relay 513 does not impulse the line relay 505 as in the case of the first digit since repeating contact 620 is shunted by a contact of 520. The manner in which the digits are repeated over the junction (neglecting the first repeated digit) and to the ticket machine is described in a subsequent paragraph The digit counting chain 531-538 has relay 535 operated after the 5th and last digit, whereupon 526, Fig. 11, opens the circuits of relay 516 and the receiving magnet 545 and, when 519 releases on the opening of off-normal contacts 709 of the mechanical repeater, 501, Fig. 7, and 521, Fig. 11, pull up. The discriminator and, associated circuits then restore, to normal. Special service calls. Such a call requires 3 digits, the first two of which are 0. On termination of the first digit, 522 operates over wiper 565 of the discriminator which is not released but takes the second digit and operates 523 over wiper 566. Relay 521 pulls up and releases the discriminator and mechanical repeater after the 2nd digit has been re-transmitted. Inter-zone calls. The discriminator operates 522 after the first digit (0) as for a service call but in response to the second (1-9) 524 pulls up, releases 522, shunts the contact 620 of relay 513 to prevent this relay repeating further incoming dialled digits to 505 at the group selector, and operates 519 to initiate re-transmission from the mechanical repeater which takes place as previously described arid when the 8th digit has been sent and relay 538 of the counting chain operated, 516 operates and releases the discriminator and associated circuits. The response of succeeding equipment to the retransmitted digits, the first two of which, previously used for setting the group selectors, are required only for ticket printing, is described in a subsequent paragraph. Faults and alarms. If the distributer DDR sticks, relays 508, 527 remain operated and pulses from 736, 737 operate relays 528, 530 to bring in visible, and audible alarms, but these circuits are not completed if the distributer is held on its last contacts by absence of ground in the case of an all circuits 'busy condition since 529 pulls up and prevents 528 from holding. If the discriminator circuits remain held for an excessive 'period, relays 510 and 525 are operated in succession by pulses from 742, 743, Fig. 9, and bring in alarms. The second pulse also shunts down 502 at the group selector which removes ground from the 3rd wire to release the finder and also to release relays 506, 507 if these have been operated. Line . relay 505 also falls back and releases the selector, and the alarm relay 525 busies the discriminator. Similar alarm circuits are provided for the tariff-determining and identification circuits described in subsequent paragraphs. An alternative identification finder is brought into use if the seize