Patent GB-808000-A (GB)
Title: Improvements in or relating to final selector circuits for use in automatic telephone systems
IPC: H04Q3/00
Filed: 1956-06-05
Abstract: 808,000. Automatic exchange systems. GENERAL ELECTRIC CO. Ltd. and COLLYER, J. E. June 3, 1957 [June 5, 1956], No. 17367/56. Class 40 (4). In a final selector with two groups of wipers, ordinary lines to subscribers and first lines or lines marking first lines of PBX groups are connected to the contact banks associated with one group of wipers while the contact banks associated with the other group of wipers are devoted to PBX groups, connections being transferred from the one group of wipers to the other when a wiper of the first group encounters a busy first line or a line marking a first line of a PBX group. In the embodiment illustrated, a 200-line final selector circuit is shown with facilities for sixteen PBX groups of 5 lines each provided in the upper and normally disconnected rows of each contact bank. First line positions of the groups are marked by earth in the lower rows of contacts associated with wiper P2-1. The first line of a group is marked by battery while the last line is marked by earth in the contact bank of wiper P2-2. Busy or idle lines of the group are marked by earth or battery on the contacts of wiper P1-2 in the same way as ordinary subscribers' lines are marked on the contacts of wiper P1-1. The circuit is seized and responds to two digits in the usual way so that at the end of the rotary train relays A, B and E are energized and CD falls back to release E slowly. If the selector halts on a busy ordinary line the test relay H does not respond over wiper P1-1 and when E falls back G operates to connect busy tone. If the ordinary line is free H operates to battery over wiper P1-1 so that when E falls back CD reoperates and relay J effects ringing. Reply and release occur in the normal manner. If the selector halts in the first line position of a PBX group earth over wiper P2-1 operates wiper switching relay WS when CD falls back to initiate the slow release of E. Slow to operate relay HS responds to battery on the first line position marked over wiper P2-2 and locks up in dependence on H to immobilize relays G and J. If the first line is free H operates over wiper P1-2, E falls back in due course to re-operate CD which releases HS. The circuit now behaves as with an ordinary line. If the first line is busy E falls back and re-operates CD which completes a circuit for the rotary magnet to interact with relay G until a free line is found in which event H and G respond in series, G releasing as soon as protective earth is connected to the P1-2 wiper by H which locks up. With the continued release of G, HS falls back and the circuit; proceeds as before. If the last line is encountered busy, earth over P2-2 holds G energized to halt the rotary magnet and lets HS fall back to connect up busy tone. The first line of each PBX group may be connected in with the ordinary subscribers' lines, busy marking on such a first line being used to operate wiper switching relay WS to connect with further lines of the group. A modification of the 200-line final selector shown in Fig. 358 and described from pages 320 to 322 of Telephony, by Atkinson, comprises the provision of a third set of wipers such that the first wiper set serves ordinary subscribers and the second wiper set includes the first line numbers of PBX groups and is connected up in response to a discriminating signal from a preceding group selector. The third wiper set serves the PBX groups and is connected up by a relay responding to a wiper of the second set engaging a first position of a PBX group.