Patent GB-766902-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: GALVIN JOHN LESLIE
IPC: H04Q3/00
Filed: 1954-06-01
Abstract: 766,902. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Jan. 27, 1955 [June 1, 1954], No. 16159/54. Class 40 (4). In a system employing 200-line final selectors and five-level penultimate selectors such as are described in Specification 657,076, the transmission bridges are located in the penultimate selectors and wiper-switching in the final selector and the routing of switch operating impulses at the final selector are controlled over one of the speech conductors extending to the final selector. Penultimate selector, Figs. 1, 2. On seizure, relay A pulls up to the loop, and B, CD, HA and HB follow, the last two being ineffective at this time. Relay A then repeats the hundreds digit to VM. If this digit is odd, say 1, the release of A operates VM and the wipers are raised to the first level; and, when A re-operates, relay OH comes up over its centre winding in series with the vertical magnet contacts VMC, and with VM which holds. Relay OH shunts down CD (but itself remains held over its lower winding) and VM relapses. If the digit is even, say 2, A releases on the second impulse before CD can fall away, and removes the shortcircuit from CD; OH is held on its upper winding, the circuit through its middle winding being opened, whereupon VM releases. The re-operation of A at the end of the second impulse releases OH and shunts down CD. The even impulses are thus prevented from operating VM by the operation of OH after each odd impulse and its release after each even impulse. In each case the release of CD completes a selfdrive circuit for RM over front contacts of HA and HB. Operation of the rotary off-normal contacts on the first rotary step makes the holding of HA and HB dependent upon the conditions found on the P2 and P1 wipers respectively. Final selector in FS1 group found idle. Absence of ground on the P1 lead at the time when RMC is operated releases HB, whereupon RM and HA fall away, but HA re-operates over its right-hand winding and back HB. The re-operation of HA extends the impulse repeating circuit to wiper D (FS1), and the release of HB brings up BA which thereupon connects its low-resistance upper winding to the - 1 lead to bring up AH in the final selector (Fig. 3). If the hundreds digit is odd (OH up) battery is extended from lead 13 to the + lead to operate WS (Fig. 3) which connects up the number one set of final selector wipers. Final selector in FS2 group found idle. Relay HA releases to absence of ground on the P2 lead when RMC are operated, completes a circuit for BA, and grounds common lead 15 to indicate that a group FS2 selector has been seized. Relay HB remains operated and the impulse repeating circuit is extended to the D2(FS2) wiper. All final selectors busy. The penultimate selector is driven to the eleventh position where the 11th step contacts S operate; S1 releasing HB, and S2 extending the busy tone lead 11 to the centre winding of relay A. Relay HA is released but re-operates over back HB. Setting of final selector. The operation of AH on seizure extends the impulsing circuit from lead D to AVM; and, for odd hundreds digits, WS operates, locks to the P lead, and connects up wipers - 1, + 1, and P1. The release of A to the first impulse of the tens digit removes the short-circuit from CD which operates, thus releasing OH which disconnects battery from the - lead, and completing a circuit for the slow-tooperate J. The re-operation of A at the end of the impulse re-applies the short-circuit to CD but CD remains up until the end of the digit and J operates. The relapse of CD at the end of the digit brings up E and extends ground over the + lead and thence over AN3 (operated) to bring up BB which releases AH and connects the D lead to ARM. The release of AH connects the right-hand winding of BB in series with the upper winding of BA to hold both relays. Relay A repeats the units digit to ARM and operates CD, which is followed by OH, the rotary offnormal contacts ANR4 connecting the left-hand winding of BB in parallel with its right-hand winding. The release of CD at the end of the digit re-operates AH which disconnects the right-hand winding of BB, whereupon BA relapses and releases BB. The -, +, and D leads are thus switched through to the -, +, and P leads of the wanted line. In the penultimate selector the release of BA disconnects the slow-to-release E and, during its release time, a test circuit is completed for the called line. Called line busy. There will be no resistance battery on the P lead so that H remains down; E eventually releases and connects up busy tone from lead 11. Called line idle. Relay H pulls up, and on the release of E ringing current from lead 12 is connected up to the called line and ringing tone is reverted from lead 10 to the caller. On the reply of the called party, ring-trip relay F pulls up and connects up back-bridge relay D which operates, reverses the battery, re-operates E, and removes the short-circuit from CD which re-operates. Relay E disconnects the slow-torelease J, during the release time of which the call is metered, and disconnects the ringing tone source. Release. Calling party release is provided, the relapse of A being followed by that of B and CD, the latter busying the penultimate selector until that selector has restored its wipers, and the former releasing E, HA or HB, F, H and OH. The release of HA or HB brings down D, and that of F completes a self-drive circuit from lead 14 for RM, to restore the penultimate selector. The removal of ground from the final selector P wiper releases AH and WS, if operated. AH completes a self-drive circuit from the release alarm lead 17 for ARM and the selector restores, after which contacts AN2 remove the busy ground from the P wire. Selector held by calling party. Relays D and CD release when the called party hangs up, and ground is connected over back D and front F contacts to lead 16 so that after a predetermined time an alarm is given. The selector held is identified by the lighted lamp in series with lead 16.