Patent GB-853444-A (GB)
Title: Improvements in or relating to selector switches for use in automatic telephone systems
Inventor: HEMMINGS WILLIAM ARCHIBALD CHA
IPC: H04Q3/00
Filed: 1958-04-12
Abstract: 853,444. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. April 3, 1959 [April 12, 1958], No. 11700/58. Class 40 (4). In a P.B.X. final selector of the vertical and rotary type having access over its contact banks to P.B.X. groups of lines or to individual lines and P.B.X. groups of lines and having bank contacts additional to the speech and private bank contacts for the control of the P.B.X. hunting function, and arranged to be set on to an individual line or the first line of a P.B.X. group in response to trains of impulses representing the last two digits of a called number, the first lines of the P.B.X. groups being permanently and characteristically marked at the relevant ones of the additional bank contacts to enable the selector to hunt over the group for an idle line if the first line is busy, at least one group of P.B.X. lines is divided into sections separated by individual lines and/or a group or groups of unsectionalized P.B.X. lines, and the last line of the first section and all the lines of the second and any subsequent sections are permanently and characteristically marked at the relevant ones of the additional bank contacts in a different way from the last line of each unsectionalized group, to enable the selector to step over lines between two successive sections of the particular group and to hunt over the lines of the second and any subsequent sections. As shown, in a 200-line P.B.X. final selector employing wiper-switching, the positions of P.B.X. groups are indicated by markings on additional contact banks P2/1 and P2/2. The first line of a group is marked by negative battery and the last line of an unsectionalized group by earth, the intermediate lines having no connection. If the group is divided into sections, a positive battery marking indicates the last line of the first section and all subsequent lines of the group. Incoming call.-The selector is seized over group selector multiple GSM, relays A, B, and CD operating. The penultimate digit of the called number is dialled in and is repeated by relay A to vertical magnet VM, which raises the wipers accordingly and operates vertical offnormal contacts N1-N4. At the end of the digit A holds and CD falls back, shunted by contacts N3. Relay E operates to switch the impulsing path from vertical magnet VM to rotary magnet RM and re-operate relay CD. (If the selector was seized over conductors - 2, +2, the operation of relay E allows wiperswitching relay WS to operate.) Rotary magnet RM drives the wipers in response to the final digit, operating rotary off-normal contacts NR1-NR3. At the end of the digit relay A holds and CD is shunted out by contacts NR2, completing test circuits over relays H and HS and wipers P1/1 and P2/1 respectively assuming that wiper-switching has not occurred). After a delay relay E falls back and re-operates CD. Selector set to first line of unsectionalized P.B.X. group. If the line is idle, battery over wiper P1/1 brings up relay H, followed by relay J which connects ringing current from leads 11 and 12 and ringing tone from lead 10. Relay HS operates to the negative battery on bank P2/1 but is released by relays H and CD. On the other hand, if the first line is busy, H is not energized and, before relay E completes its delayed release, relay HS operates and brings up relay X. After the release of E and consequent re-operation of CD (which connects relay G to wiper P2/1), rotary magnet RM is energized, stepping the wipers to the second line of the P.B.X. group and operating rotary interrupter contacts R.M.C. to operate relay G. This de-energizes magnet RM which restores contacts RMC so that relay G now depends upon the busy or idle indication on bank P1/1. If the line is idle (battery marking), G holds on its left-hand winding. If the line is busy (earth marking), G falls back and magnet RM steps the wipers to the next line. The selector continues to hunt, controlled by the interaction of magnet RM and relay G. If all lines of the group are busy, the selector reaches the last line. As it does so, contacts RMC are operated and relay G is energized over its right-hand winding. When magnet RM restores contacts RMC, G holds on its right-hand winding to the earth marking on bank P2/1. After a delay, relay HS falls back, releasing relay X and applying busy tone from lead 13. If, on the other hand, an idle line is found, relay H operates in series with G. Relays G, HS, and X are released and relay J is energized, connecting ringing current from leads 11 and 12 and ringing tone from lead 10. When the P.B.X. operator answers, relay F operates to the D.C. loop on the line, trips the ringing and switches through, bringing up relay D which reverses the polarity of the incoming speech wires and also energizes relay E. This connects positive battery to the incoming P-wire as a metering signal and disconnects relay J, which releases after a delay and ends the metering signal. Selector set to first line of sectionalized P.B.X. group.-Hunting takes place over the first section as for an unsectionalized group, until the last line is reached, this also being assumed to be busy. The positive battery marking on bank P2/1 energizes relay Y, which makes relay X dependent upon the marking on bank P2/1 and releases relay G so that magnet RM steps the wipers to the next line. This is not one of the P.B.X. group and is therefore not marked by positive battery on bank P2/1. Relay X falls back and disables the test circuit over wiper P1/1. Magnet RM and relay G interact to step the wipers until 11th step contacts S1 are operated or another line of the P.B.X. group is met, marked on bank P2/1 by positive battery which re-operates relay X to restore the test circuit so that hunting is resumed. Selector set to any line other than the first of a P.B.X. group.-In this case there is no negative battery marking on bank P2/1 and relay HS is inoperative, so that the selector tests only the one line and does not hunt. The customary alarm leads 14, 15 are provided.