Patent GB-682244-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone or like systems
Inventor: BEALE CHARLES EDMUND
IPC: H04Q3/00
Filed: 1949-09-21
Abstract: 682,244. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Aug. 31, 1950 [Sept. 21, 1949], No. 24211/49. Class 40 (iv). In a bidirectional P.B.X. final selector which provides for groups occupying more than one level, testing takes place over two sets of wipers simultaneously and if all lines in one level are unavailable the switch releases rectangularly and is automatically set to hunt over another level having access to further lines of the group. If all the lines in the group are unavailable the wipers are stopped on the last line of the group and an individual overflow meter is operated, busy tone being returned to the calling party. Operation of selector. After the selector has been set by two digits in the normal way, the release of dialling relay C completes testing circuits over relays HA, DR to wipers P1/1, P2/1 respectively and initiates the slow release of change-over relay E. Assuming that the wipers have been set at the start of a P.B.X. group marked by battery on bank P2/1, four possibilities arise, as follows. (i) Wiper P1/1 encounters the P-wire of an idle line (battery) and P1/2 the P-wire of a busy line (earth). Relay HA seizes the idle line over wipers -1, +1, P1/1 and DR brings up DS. When E releases, DR and DS release and C and J are energized to initiate ringing and prepare for metering. (ii) P1/1, P1/2 both find idle lines. The selector operates as in (i) above, as HA prevents operation of HB. (iii) P1/1 finds a busy line, P1/2 an idle line. DR, DS operate and relay HB seizes the idle line over wipers - 2, +2, P1/2, applying a tone signal to jack TJ1. J extends ringing current as before. (iv) P1/1, P1/2 both encounter busy lines. DR, DS operate as before and the release of E energizes the rotary magnet RM which interacts with interrupter contacts RMC and relay G to step the wipers in search of an idle line, DR remaining locked meanwhile. If the 11th position of the level is reached without an idle line having been found, the P.B.X. group being continued on another level, contacts S1, S2 are mechanically operated. Relay RN releases DR, DS and connects level discriminating relays DW, DX, DY, DZ to wipers +2, - 2, +1, -1 respectively. Some of the 11th step contacts of these wipers are earthed according to a code indicating the next level to be hunted over, e.g. contacts X, Y on level 4 are earthed to indicate that the P.B.X. group is continued on level 3. Relays DX, DY operate and mark level 3 on an auxiliary vertical bank AB. Rotary magnet RM by self-interruption at RMC causes a 12th step of the wipers which return to normal together with the S, NR and N contacts, magnet RM and relay RN. Vertical magnet VM by self-interruption at VMC raises the wipers until, at level 3, auxiliary vertical wiper AW shunts and releases C, which disconnects VM and brings up DR, DS. Level discriminating relays DX, DY release, and rotary magnet RM starts the wipers hunting as before. All lines busy in P.B.X. group. On the last position of the group, wiper P2/1 encounters earth which operates relay G to stop the wipers and release DR so that an overflow meter is energized over wiper P2/2 until the completion of the release of DS which then applies busy tone. Night service or selection of individual line. Those lines accessible over wipers -1, +1,P1/1, except the first of a P.B.X. group, are available for individual selection. The wipers are set by the appropriate two digits and, since the position is not marked by battery on bank P2/1, DR is not operated and only a single outlet is tested, over wiper P1/1. If the line is idle it is seized by HA as before. If it is busy, the release of E brings up G to apply busy tone. Called party replies. The D.C. loop on the - and + wires enables relay F to open its shunt contacts and then operate fully to cut the ring- ing and switch through. Supervisory relays D, DW operate and the caller's meter is energized from lead 12 until the release of J is completed. Release of the selector is normally controlled by the calling party, but last party release may be provided by adding the connection shown dotted near contacts N2. Failure to hang up initiates a delayed alarm over lead 16. The switch mechanism is of the type described in Specifications 391,151 and 450,019. Specifications 451,667 and 479,852 also are referred to.