Patent GB-892719-A (GB)
Title: Improvements in or relating to automatic telephone systems
Inventor: PARIS HOWARD VAREY
IPC: H04M3/08
Filed: 1959-05-22
Abstract: 892,719. Automatic - exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. May 20, 1960 [May 22, 1959], No. 17416/59. Class 40 (4). In an automatic telephone system employing a line connector for associating subscribers' lines at a remote point with corresponding line circuits at an exchange over a number of links smaller in number than the number of subscribers, a battery at the remote point, for operating the line connector switch gear, is charged from the exchange, there being automatic means for adjusting the charge rate in accordance with the load connected to the battery. Twenty-four subscribers' lines SL gain access to the corresponding " + " and "-" wires at the exchange via line-finder LF, link LL+ and selector finder SF. At the remote unit, equipment individual to a link (there being four links) is designated LER and at the exchange LEE, equipment common to two or to all four links being designated CER and CEE respectively. The link allotter LA in CEE allots free links in either direction on a cyclic basis; the outlets of LA are multipled in groups of five, the first four of a group being associated with the four links while the allotter is held on the fifth outlet when all the links are busy. Initial setting of a link equipment.-Exchange battery is connected up and the relay CHS in each of the four link equipments LEE operates in a circuit over appropriate link conductor L+, L- and relay OC (not energized). LA magnet is thus energized and drives LA switch from a fifth outlet to a free link equipment, when relay LKA pulls up, so de-energizing CHS and breaking the driving circuit. Consequently relay CS is energized, which operates CO to produce a reversal of the line conductors connected to CHS, and which also applies positive battery via R3 in CEE to a link control wire LC so operating relays X and Y in CER with subsequent pulling up of relay CL. Two link equipments use one control wire LC but the second relay, 2CS (not shown), introduces resistance R5 so that only X will operate and hence only 2CL which is in the second equipment at the remote unit will operate. The operation of CS and 2CS simultaneously is prevented by a contact of an operated one of these relays shorting out the other unoperated relay. CL in operating allows SA in LER and CHS in LEE to pull up in series, thus serving as an acknowledgement to the exchange that the remote unit is operating satisfactorily. The energization of CHS releases CS and hence X and Y, but SA, LKA and CO and CHS are held. Charging branch battery.-A trickle charge to the remote unit battery is normally applied via relay TC, resistance R4 and the link control wire, rectifier MR4 preventing positive exchange battery from reaching the branch battery and contacts CS3 (or 2CS3) preventing operation of TC when CS operates. The remote unit battery is preferably a nickel-cadmium cell but the normal lead-acid type may be used. Call from a subscriber.-Looping of a subscriber's line SL causes the operation of relay LR which then provides a mark condition on level LF2 of the line-finder switch, and also closes the operating circuit of start relay STR. A new holding circuit for SA is thus made, CHS being released and as a consequence start relay ST in the allotted link equipment LEE is operated. Relays J, PO and CD are energized and in so being, bring up relay A in LEE and relay AR in LER. Selector finder magnet SF and line-finder magnet LF are energized and on the release of PO (A operated) and AR, the line and selector finder switches are then stepped to the next contact. The interaction of PO and A causes the synchronous stepping of the switches until the calling line is found, when relay ER operates and opens the series operating circuit of A and AR. A relay ON energized by the first step of the selector finder, releases CD at the end of impulsing, relay STR and consequently SA also releasing then. Release of SA brings up relay LCO with consequent de-energization of line relay LR. Release of CD at the exchange end brings up relay H and relay GS is also operated if a mark condition, in the form of an earth on CCL, is present on the " p " level SF2. H brings up LK and disconnects ST and hence J, LKA and CO. The subscriber's line is now extended to the common calling circuits CCC or the selector finder banks depending on whether GS is or is not operated and also the link allotter has been driven on to the next free link. Charging branch battery during call.-Operation of relay H, described above, closes a further charging circuit via resistors R9, R10 and link control wire to the remote unit battery and relay ACC then operates. If a second link equipment relay (2H not shown) operates, R10 is shorted out and the charging rate is thus increased, the trickle charge through relay TC (not operated) being maintained at all times. If further link equipments are in use the charge rate is increased still further. Call from exchange.-Relay LL in the calling line circuit is operated by earth on the P-wire of the exchange appearance. Subsequently, ST is energized and the above described sequence of events put into operation. In this case however CHS is released by J and not by SA and the calling line is detected, when the selector finder wiper SF2 finds battery potential, by relay E which then releases A and AR. Release.-Battery potential is applied to the P-wire at the exchange, thus energizing relay PC. Therefore H is released, the extra charging circuit is thus opened and CS is operated. CS closes the homing circuit of the selector finder and also via relay CL in the remote unit closes the homing circuit of the linefinder. When the line and selector finders have homed with subsequent de-energization of CS and CL, the trickle charge to the remote battery which was temporarily cut-off due to the operation of CS, is resumed, and CHS and LKA are operated so that the link can be seized by the link allotter for the next call. Fault detecting.-The occurrence of faults on a link control wire or a fuse failure at the remote unit causes the operation of relay TC which then closes a circuit to the alarm wire AL. Faults on the link are detected by relays CHS or DF depending on the exact nature of the fault, but in either case earth is applied to the alarm wire AL. Relay OC operates if the fault current is large and in so doing limits the current through CHS and DF. All links allotted, Fig. 4. The last link, i.e. the fourth, being taken into use, relay LE which is normally held via the earth applied to the home contact of level LF1 of the linefinder switch in one of the four link equipments, is released by the de-energization of STR when the calling line is found, and in so being introduces a high resistance R12 into the common battery circuit of line relays LR. When a subscriber's line is next looped, the current is insufficient to operate LR but is sufficient to energize the telephone. Hence battery drain at the remote unit is effectively limited.