Patent GB-303552-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04M7/06
Filed: 1927-10-05
Abstract: 303,552. Standard Telephones & Cables, Ltd., and Wright, E. P. G. Oct. 5, 1927. Addition to 268,862. Automatic exchange systems.-A subscriber on a satellite is connected to a discriminating selector-repeater associated with a non-numerical switch W5 - - W10 which over one set of wipers selects a junction to the main office and subsequently, in the case of certain combinations of the first two digits, releases the main office and selects a junction to a neighbouring satellite over a second set of wipers. In this case, the se:lector-repeater is restored and responds to the third digit, which is repeated to the neighbouring satellite, to determine finally the destination of the call. If the call is a local one, the selectorrepeater hunts for a local selector and on finding it releases the junction to the neighbouring satellite. Non-numerical switching arrangements. The switch W5 - - W10 hunts for a junction in the same way as the corresponding switch in the parent Specification except that it tests over the terminals to which the chain relays CH are connected. Discrimination between main office and other calls. Relay A repeats the first two digits to the magnets V, R and, over T.15, T.17, to the main office, the dialling relays, C, E, short-circuiting the inductive bridge J, D. If the call is for the main office, wiper W.2 is now resting on a terminal jumpered to T.9, and when E falls back, P pulls up, locks itself, disconnects the rotary magnet and polarizes the supervisory relay J. If the call is not for the main office, W.2 is on a terminal jumpered to T.8, and Q which is in parallel with P but was unable to pull up over the resistance R.2 connected to T9, pulls up also, energizes the release magnet Z and releases the switching relay K of the hunting switch. Discrimination between local and neighbouring satellite calls. When the selector repeater reaches normal, the switch W.5 - - W.10 hunts again, using its second set of wipers which is connected up by Q, P is released, and M pulls up, disconnects the release magnet, transfers the discriminating ground from T.8, T.9; to T.7, disconnects the rotary magnet from the impulsing circuit and causes the stepping relay G to pull up as soon as the selector repeater moves. At the end of the third digit, the relapse of C energizes the rotary magnet which unlocks G. If the call is for the neighbouring satellite the terminals encountered are dead. If however, the call is a local one, wiper W.2 is on a terminal jumpered to T.7. and P connects G to the test wiper W.1. The rotary magmet and G then interact in the usual way until an. idle local selector is found whereupon H switches through, releasing K to free the satellite. Busy tone arrangements. If all the main office junctions are busy and the call is for the main office, the operation of P sends back busy tone from T6 over a back contact of K. In a call for the associated satellite, if all the junctions are busy the non-operation of K makes a local circuit for G and the rotary magnet, and the-selector repeater goes to 11th terminals changing over springs S to stop itself and send busy tone as in local calls. Dialling tone arrangements. Dialling tone T-5 is initially connected up over the lower winding of line relay A and is cut off when the selector moves up. When the selector is restored after two digits the tone is cut off at once by M.