Patent GB-432281-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1934-01-24
Abstract: 432,281. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool, BAKER, G. T., Blackbrook, Caerphilly, Glamorgan, and RICHARDS, 1. T., Ealing, Renville Road, Liverpool. Jan. 24, 1934, No. 2527. [Class 40 (iv)] In a satellite system, the numbering scheme of which is shown in Fig. 10, (the circuits described being those of office L, the initiation of a call causes the seizure by an allotting switch SED of a discriminator set DRS which associates itself with the calling line over a switch SCF and seizes a junction to the main office by means of a switch JA. Switch DD then responds to the first or first two digits and if the call is for the main office a switch GF belonging to the seized junction hunts for the calling primary finder PF and the discriminator circuit is restored to common use. If the call is for the local office or for one of the offices reached independently of the main office the junction is released and a switch JB hunts for a local link LOC or for a junction ADJ, in the appropriate direction. The switch GF of the seized circuit then selects the calling primary finder and the common apparatus is released. In case of spare number calls or of an all-trunks-busy condition, JB hunts for a busy and NU tone set BNU which makes connection with the calling line in a similar way. In case all the direct junctions to an adjacent office are busy the call may be set up via the main office junction, the release of which is prevented. Certain primary finders may be connected to the banks of secondary finders as described in Specification 376,265 and the switches GF arranged to hunt for these. Allotting circuits. The primary finders may be allotted by circuits similar to those described in Specifications 376,265 and 429,767 in the condition in which all regular primary finders are busy. When a primary finder is taken into use a circuit is made over SS, S for DS unless OB is de-energized because all the discriminator circuits are in use. DS locks up and connects up DK in the allotter shown and the corresponding relay in another allotter SC2 not shown in detail. Since the allotters are pre-selecting, both relays DK should operate immediately, but if they do not the switches hunt. DK on operating removes a shunt from DR, the initial operating current of which flows in the lower winding of DK in a de-energizing direction. This is without effect unless two allotters are attempting to switch through on the same discriminator. In this case both relays DK start to release but one will open its contact dkl first and the other is then able to hold. DR is made sluggish by a short-circuited winding to give time for this operation. On pulling up it shunts out DK, locks itself and makes circuits whereby the switch SCF in the discriminator circuit hunts for the calling finder under control of FK in the allotter. FK, FR cooperate in the same way as DK, DR to guard against double connections but DK remains operated after DR pulls up in series with a relay in the primary allotter circuit (not shown). The primary allotter is then released and DS, FK fall back in the allotter CS1. G then pulls up and interacts with SEM in the pre-selection of a new discriminating circuit. Discriminator circuit. When the allotter switches through, SCF hunts for the calling finder as described above, AA and BB pull up and, unless all the junctions to the main office are busy, BZ marks the main office junction positions in bank JA8 and makes circuits whereby JA hunts with its wiper JA7 for one of these junctions under control of LK. LK, H co-operate in guarding against double connections in the same way as DK, DR but LK remains locked up over a low resistance winding to busy the junction. When SCF is stopped, PK switches through and AA is held over the loop. H unlocks BZ and energizes HZ which transfers the loop from AA to A in the junction circuit. AA, BB, therefore fall back and A, B, JG pull up, LK is shunted out and a loop D, I is put across the outgoing junction. On the relapse of BZ, dialling tone is sent back. One or more dialled digits are repeated by A over the junction, C being operated during each digit to give a clean impulsing loop, and also over CC to the driving magnet of the discriminator switch DD. If the first digit denotes a call to be set up via the main office (digits 2, 3, 4, 6 and 8) wiper DD4 is on a terminal connected to 1DS (lower) and on the relapse of CC, 1DS is operated in series with ZC (right hand). ZC is not operated and 1DS locks in series with MH (left hand) which locks up. 1DS also holds BZ, which is re-operated over DD3 and the busy common of the main office junctions, and energizes HR which shunts its high-resistance winding to make it impossible for another HR relay to pull up over the common resistance 1YA and over 2YA marks the calling primary finder in the bank gf of GF. HR also makes a driving circuit for GF which then hunts under control of CK. CK on operating reenergizes CC and allows SK in the junction circuit to switch through. SK locks up and shunts out CK to release CC. A temporary circuit is thus made for CO which locks itself and unlocks PK to release the discriminator relays and home switch DD. If the call is for Sat3 (first digit 5) DD5 will be set to a terminal jumpered to SAT3 to mark the proper junctions in bank JB8 and DD4 will be set to a terminal jumpered to 2L. As a result, SW pulls up on the relapse of CC, locks itself, connects up JBM in place of JAM and energizes 1DS which opens the impulsing circuit to DDM and releases H, HL (which in this case have no holding circuit over DD5). AA, BB pull up again, the main office line is released and JB hunts for a junction in the same way as JA under control of LK, after which H, HZ pull up to connect the impulsing circuit to the impulse relay of the junction circuit and HR causes the switch GF of the selected junction circuit to hunt for the calling line-finder. In the case of local calls or calls to Sat1 (first digit 7) DD5 at the end of the first digit finds itself on a blank terminal and DD4 on a terminal jumpered to DA. MH therefore pulls up and locks and 1DS is not operated. DDM then advances to a second home position in readiness for the second digit after which, in the case of a local call, SW pulls up and JB hunts for a local link or, in the case of a call to Sat1, 1DS pulls up without SW and JA hunts for a junction. Similarly in the case of zero calls JA hunts for a circuit to an operator. In the case of spare codes ZC (middle) is operated as well as 1DS, MH, SW and since BZ is unoperated (DD3 being on a blank terminal) JB hunts for a busy and NU tone set which then associates itself with the line as in the case of busy conditions described below. With ZC operated however, low resistance ground is connected over SW to the set when CO operates to cause it to send NU instead of busy tone. Busy conditions, alternative routing. If all the junctions to the main office are busy, BZ is unable to operate when BB is operated on the seizure of the discriminator circuit. The switch JA therefore does not hunt and dialling tone goes back at once. The switch DD responds to the first digit which in this case is repeated to it by AA, and if the digit denotes a main office call, the circuit over DD4 energizes SW as well as 1DS. MH also is energized and as a result ground over 14, LK (both windings in series) and terminal 1BU is connected to terminals in bank JB8 corresponding to busy and NU tone sets, and at the same time a driving circuit is made for JBM. The switch therefore hunts with its wiper JB7 for such a set. On the operation of LK to stop the switch H, HR pull up and a switch similar to GF associated with the seized tone set is driven to the calling primary finder. In case all the tone sets are busy, JB picks up a local link since these also are marked over bz4 and the corresponding switch GF hunts for the calling primary finder. On the subsequent release of the discriminator set the impulse over DD4 which in effective calls energizes ZA, ZB, energizes a relay in the local selector which sets up a busy condition therein. Similarly if all the local selectors or all the junctions to the wanted satellite office are busy BZ is unable to re-operate over DD3 and in the case of local calls or calls to Sat1 a tone set is picked up. In the case of calls for which there is an alternative route via the main office however, H, HZ remain locked up over terminals RER, ME and the call proceeds over the main office switches. Zone metering. Wiper DD4 of the discriminator in outgoing calls selects one of the terminals jumpered to -Z1 .. Z4. On the release of the discriminator, between the operation of CO and the relapse of PK, circuits are made for the operation of either or both of the relays ZA, ZB if one of the terminals Z2 .. Z4 was selected. If Z1 was selected neither relay is operated. These relays lock up and select the appropriate metering wire which is connected up for a suitable period shortly after the operation of the supervisory relay D in the junction circuit with the help of S and Z relays DA, DB. If desired a time measuring switch may be associated with the junction so that metering may be on a combined time and zone basis. Restricted service to coin boxes. When an outgoing call is attepted from a coin box station a junction is seized as described above but when SK switches through, CB is energized over the metering wire M which is connected to battery in the coin-box line circuit. CB locks up and bridges the wires SW, DM. If the subscriber has set DD4 to a position corresponding to a barred zone (i.e. one jumpered to Z2; Z3 or Z4) ZB pulls up and connects battery over the magnet GFM to SW to operate ZC (right hand). ZC locks up (middle), energizes CO in series with GFM and releases BZ, H, HZ. GFM operates and releases SK to free the main office. HZ re-connects AA which is followed by BB which prevents the