Patent GB-616834-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone systems
IPC: H04Q3/62
Filed: 1946-06-07
Abstract: 616,834. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., JONES, E. W., and PEARCE, O. A. June 7,1946, No. 17320. [Class 40 (iv)] A digit-absorbing switch is set by the initial impulses of the first train received and then restores to normal during the reception of the remaining impulses, which cause circuit changes enabling a selection to be made amongst the groups of lines to which the switch has access. In this way the time available for the restoration of the switch is increased beyond the normal inter-digital pause. An auxiliary bank, preferably of the type disclosed in Specification 391,151, is provided over which special service circuits, e.g. fire alarm circuits, may be taken into use. The switch is also equipped to allow breaking-in on busy connections by privileged subscribers. Specification 588,563 also is referred to. The switch described is a P.A.X. final selector having access to 200 subscribers over two 100-point banks, and to ten special service trunks over an auxiliary vertical bank. The preferred numbering scheme is 200-299 and 300-399 for the two 100-line groups and 40-49 for the special service trunks. Relays A and B operate on seizure, dial tone from lead 12 is transmitted and the supervisory lamp LP is connected to the delayed alarm lead 15. Call to party in 1st hundred-line group. Relay A responds to the initial digit 2, and on its first release operates C and raises the wipers to level 1, whereupon the normal post contacts NPA operate. The operation of the vertical off-normal contacts extends battery to the common lead 14 and a low resistance alarm earth is returned over lead 13. This earth is extended to the rotary magnet when the reoperation of A to the first " make " of the dial brings up DA, and restores the selector to normal. Relay DA also cuts off the dial tone and prevents further vertical stepping. The second release and subsequent re-operation of A bring up BA and W respectively and when the selector has restored DA and W fall away. The second digit raises the wipers to the corresponding level, and the relapse of C at the end of the train brings up E which directs the third digit to the rotary magnet. Relay E is disconnected by C at the end of the third digit, and during its release time the test relay H is connected to the P1 bank. If the wanted line is idle, H operates and the relapse of E connects up ringing current and ring tone from leads 16 and 10 respectively. On the reply of the called party, F trips the ringing and connects up back-bridge relay D which thereupon operates and switches the connection through. If the wanted line is busy, the release of E connects busy tone from lead 11 to the calling party. Call to party in 2nd hundred-line group. In this case the initial digit is 3 and operation is as above up to the energization of W on the second " make" of the dial. Upon the third " break relay WS operates and switches the outgoing conductors to the second set of wipers. Relay E comes up on the third " make " and operation thereafter is similar to that described above. Special service call. The initial digit 4 is dialled and operation is as above up to the energization of E on the third " make " of the dial. The fourth " break brings up SS which releases BA and WS, of which BA transfers the test circuit to the auxiliary wiper AP. When the wipers restore W and DA fall away and E is re-operated. The second digit steps the wipers to the appropriate level and, on the release of C, H is connected up and operates to battery in the special service circuit (not shown) during the release time of E. The release of E re-operates W which extends the SSM bank contact, which is connected to earth over a cut-drive relay in the special service circuit, to lead M2 over the wiper AM. When the line-finder of the special service link circuit reaches the calling line, this earth is extended over the line-finder multiple to battery in the link circuit and operates the cut-drive relay to stop hunting. The final selector shown is released and the necessary alarm and calling line identity signals are transmitted over the special service link-circuit and a final selector associated therewith. Breaking-in. Priority subscribers have the M2 lead connected to ground over a resistance of sufficiently high value to prevent the cutdrive relay of the special service link being short-circuited thereby. If busy tone is returned to him, a priority subscriber may dial the additional digit O. Relay C then comes up for the duration of impulsing and charges condenser QA over a circuit to the ground on M2. On the release of C, CR pulls up followed by D which switches through to the established connection and re-operates E. The priority subscriber instructs the parties engaged in the connection to hang up, and when they comply, H operates, CR, D and E release, and the connection is established in the normal manner. Release. Last party release is provided. In the case, say, of a connection to a party in the 2nd hundred-line group, relays A, B, D, F, H, BA and WS will be operated. If the called party hangs up first, D falls away and connects LP to the delayed alarm equipment, which operates only if the calling party does not hang up within a specified period. If the calling party clears first, A relapses, short-circuits B and brings up C. Relay B falls away, operates E, releases BA and WS, removes the busy earth from the P-wire, and short-circuits C. When the called party hangs up the release of D, which is followed by that of H, F and E, extends battery to lead 14, whereupon earth is returned over lead 13 as above, so that when E makes its back contacts the switch releases. Dialling of unallotted prefix digits. In all such cases relay DA remains up after the switch restores and busy tone is reverted. If desired, the numbering scheme may be altered, the normal post contacts NPA being set to operate on that one of the levels 1 to 7 immediately below that allocated to the 1st hundred-line group. The further set of normal post contacts NPB is then set to operate on all levels preceding that on which NPA operates, to bring up DA and revert busy tone at the end of the first train, the wipers releasing over the level corresponding to the digit dialled.