Patent GB-368846-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-12-12
Abstract: 368,846. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd. (formerly AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd.), Strowger Works, Liverpool, and OLIVER, E. C., 229, Sea Bank Road, Wallasey, Cheshire. Dec. 12, 1930, No. 37580. [Class 40 (iv).] In a 10-line system, the common impulse recorder is associated with the calling line only while the dial is off-normal, the association being controlled by a circuit including a 3rd wire to the substation and off-normal springs of the dial. The 3rd wire is used also for operating the bell. The ring cut-off relay is shunted by a metal rectifier and is kept energized by the ringing current. Seizing and operating register-marker. When the dial is moved off-normal a circuit is made (unless both links are busy) for 1LP or 1LQ, depending on the condition of SW, to connect the line to a link in which (assuming the lower to be used) 1SC pulls up its light armature 1sc1 to lock 1LP and energize 1BK which busies the link by disconnecting the energizing windings of all relays LP. SW is arranged to operate after 1sc1 and is replaced at 1sc2 by the impulse relay I of the registermarker in which B, E also are energized, but remains locked until a new call is made. As the dial returns, I repeats the impulses to the counting relays P .. U. C pulls up at the first impulse and locks so that E holds only until the end of the digit and then grounds the selected one of the marking wires 1 .. 0 and energizes the marking relay 1FM which connects the right-hand windings of the LP relays to their marking wires and energizes the upper feed relay 1FB which connects itself to one talking wire and the lower feed relay 1FA to the other and releases the register-marker in which relay B falls releasing 1FM, 1SC. Busy test and ringing ; busy release. Ring- ing current on 21 if the line is idle and there is therefore a path through the wanted party's bell energizes the relay 1F which is shunted by a metal rectifier. 1F energizes 1FR. When the call is answered the bell is disconnected and these relays fall back. If the line is busy there is no path for ringing current and IF, 1FR are not operated. Consequently, the release of 1FM is prevented and when 1SC falls, LP is unlocked and the release of the link follows. The calling party recognizes that the line is busy by the absence of the ringing signal which he normally hears owing to the presence of the common feed relay 1 FA in the return path of the ringing current. Simultaneous calls. As soon as the registermarker is seized, a short circuit is removed from TE. If a 2nd call is made at this stage, the relay SC of the other connecting circuit being unable to operate in series with TE, the impulses are without effect. TE holds while the 2nd dial is off normal independently of the condition of the register-marker. Current supply. Ringing current at 75 volts is provided by the upper secondary of the mains transformer XFR. The lower, 16-volt winding feeds a rectifier RCU, from which the current is smoothed by means of chokes 1CH, 2CH and electrolytic condensers 1EC, 1EC. To make the load more constant, resistances YF, YG are shunted across the supply except while the low resistance counting relays are being operated. To avoid interference, the feed for the control relays is separated from that for the feed relays by being connected between the two chokes.