Patent GB-493656-A (GB)
Title: Switching arrangements in selectors for use in automatic telephone systems
IPC: H01H67/02
Filed: 1937-07-15
Abstract: 493,656. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. July 15, 1937, No. 19666. Convention date, July 17, 1936. [Class 40 (iv)] A switch comprising a number of successively operated change-over contacts, e.g. as described in Specification 459,299, is used to make connections between a group of subscribers' lines and a common exchange line, the switch operating as a finder for outgoing calls and as a numerical switch for incoming calls. In a modification providing for conversation between subscribers of the group, a further similar switch is used as a numerical switch. Automatic switching centre, Fig. 1, for connections between an exchange line SL and a group of subscribers' lines 1-10. The lines are connected to the movable contacts which are normally in the lower position so that a calling loop is extended over individual contacts, the first contact K normally in the upper position, and rectifier L1 to the line SL. This causes transmission of impulses from the exchange over rectifier L2 to magnet VM and the first step of the switch opens K to disconnect all the subscribers, lines, except the first which is connected up by changing over contacts a1. At the next step, a1 restore and a2 connect line 2 and so on until the calling loop is reached, whereupon the impulse sender is disconnected. All other lines are shortcircuited over contacts K to which a busy signal may be connected. On release, the opening of the loop causes re-connection of the impulse sender for stepping the switch to normal, the impulse sender being disconnected in response to ground on the last contact of the switch. For an incoming call, the switch is set by numerical impulses. Modification, Fig. 2, for permitting conversations between subscribers of the group. Two switches AS, LV are provided, the lower line-contacts of AS being connected to the movable contacts of LV. When a subscriber calls, the loop is completed over corresponding contacts of both switches, the normal position contacts of AS, relay R and rectifier L11, and the switch is set on the calling line by magnet ASM in response to impulses as previously described. Relay R, slow - to - operate and release, does not pull up until the loop is permanently closed and does not respond to impulses sent by the calling party. If the call is a reverting one, the exchange sends the required number of impulses which are directed by relay R to magnet LVM to set switch LV which connects up the wanted line. On release, R falls back and the impulses from the exchange are first directed to magnet LVM over operated normal position contacts 41 of LV until this switch reaches normal whereupon the impulses are directed over 41 to ASM which steps out as previously described. Incoming calls are set up over AS as previously described. By placing relay R and its shunt condenser C in the upper bar of switch AS between the normal and first line contact positions, it does not receive current until the switch is set on the subscriber's line. Also, the relay may be shunted over the lower normal-position contacts of LV when this switch leaves normal, the circuit for magnet LVM being maintained over the upper contacts 41.