Patent GB-571994-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04Q3/62
Filed: 1944-01-22
Abstract: 571,994. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., McCLEW, J. W., and PEARCE, O. A. Jan. 22, 1944, No. 1250. [Class 40 (iv)] An allotter for a group of finders consists of a number of relays, one for each finder, connected to the junction points of a closed chain of rectifiers and a continuously-driven switch for applying a starting potential progressively to the said junction points so that the finders are rendered first choice in succession. A 100- line private exchange system is shown in Figs. 5-10, made up of three identical 35-line units each provided with four finder-connector links and a relay allotter, and each link comprising two 50-point finders serving the "under 50 " and "over 50" groups and a 100-point connector. The units normally operate independently, but if all the links of a unit are in use, further calls from the lines of that unit are transferred to the next unit, this being possible as the finders of each unit have access to all the lines. The requirements for smaller systems needing only one or two units are mentioned. Provision is made for giving priority to certain privileged subscribers, the strap P, Fig. 5, being used in their line circuits in place of the strap O. On a call from an ordinary subscriber in the "under 50" group, line relay LU applies marking potential in the finder banks US4 and starting potential to relay UF of the allotter AEU1 and also over wire 30 to the first transfer relay UTA of the allotter AEU2 and to the second transfer relay UTB of the allotter AEU3. Provided there is an idle link in the first unit, busy relay GR is back and relay UF energizes, disconnects wire 30 and grounds wire 7 leading to wipers W1, W2 of the continuously-driven sequence switch SMD. With the wipers in the position shown, ground is extended over wire TL1 to relay FS in the link U1/L1, via rectifier MRB and contact fs8 to relay FS in the link U1/L2, and so on. If the link U1/L1 is idle, contacts N1 are closed, and its relay FS energizes and disconnects the later choice FS relays. Relay FS locks, connects up busy relay GR, holds UF and operates line relay A which starts the finder US. When the calling line is found, test relay FT brings up switching relay SW, and relay FS releases, followed by FT, UF, GR, leaving the allotter AEU1 free to deal with further calls. For calls in the '' over 50 " group, line relay LO (not shown) energizes relay OF in place of UF with similar effect, except that relay CO is operative to connect up the finder OS serving that group. Relays UF, OF disconnect each other, so that simultaneous " under 50 " and "over 50" calls in the same unit are dealt with successively. It will be seen that wiper W1 prepares over wires BL1 &c. short-circuits for the FS relays over its contacts, which are shorter than those of W2, and therefore an FS relay can operate only when W1 is between contacts. Moreover, if an FS relay remains operated for an excessive time, its circuit is opened by wiper W2 and the FS relay of the next idle link in the unit is energized. To prevent repeated seizure' of a faulty finder when it is the only idle one in the unit, busy relay GR is held temporarily by the operation of dialling relay C (not shown) when the link is released. If all the links in the first unit are busy, GR is operated in a chain circuit, and the starting potential energizes UTA or OTA in the allotter AEU2 to allot a link in the second, unit. If, however, busy relay GR of that allotter is up, the starting potential is further extended to. energize UTB or OTB of the allotter AEU3. Relay GR when energized in any unit prevents the operation of any of the transfer relays of that unit, and a potential applied to wire V when any transfer relay is up, prevents the operation of relays UF, OF in that unit. In the case of calls from privileged subscribers, all of whom are located as shown in the "under 50" group, relay PR operates in each unit and opens the start circuit of all " over 50 " subscribers and the start and marking circuits of all ordinary "under 50" subscribers. A priority start circuit is extended to UF, which has preference over OF in the event of a simultaneous "over 50" call. If UF is already up, it is maintained and the allotted finder deals with the priority call. If an ordinary "under 50" call is being handled by UTA or UTB in the first unit, say, relay PR will operate UTA in the second unit and the. operated relay UTA, UTB will be released until the priority call has been extended. Similarly, if an ordinary "over 50" call is being handled by OF, OTA or OTB in the first unit, this relay will be released until the priority call has been dealt with by UTA in the second unit. On a priority call, a local circuit is made for back-bridge relay D to permit cutting in on a busy line. Should a connector remain off-normal through a fault, relay FS is disconnected and a point is closed in the chain circuit for busy relay GR. Similar conditions prevail when a link is under test. If the sequence switch SMD stops with only wiper W2 making contact, all the links can be used, but if both wipers make contact, one link remains out of service : this could be avoided by disconnection of the wires BL1 &c. when this fault occurs. Specifications 389,867 and 462,910 are referred to.