Patent GB-709504-A (GB)
Title: Means for identifying and marking telephone calls
IPC: H04M15/08
Filed: 1952-07-04
Abstract: 709,504. Automatic exchange systems. TELEFONAKTIEBOLAGET L.M. ERTCSSON. July 4, 1952 [July 5,1951], No. 16887/52. Class 40 (4)  In a calling line identification system, a multi-electrode glow discharge tube is provided for each line and is of the type which when fired strikes across the starter gap only, the remaining gaps being capable of striking only in a predetermined sequence. As described, there is one "remaining" gap for each digit in the numbering scheme. The hundreds digit cathodes of lines having the same hundreds digit are commoned and these are impulsed cyclically, the first tube whose starter gap is fired (line in calling condition) firing across its hundreds digit gap and stopping further impulsing. The tens cathodes are similarly impulsed, but only that tube whose hundreds gap has fired can fire across its tens gap. Similarly only that tube whose tens gap has fired can fire across its units gap. The positions in which impulsing is stopped are registered and give a record of the calling line number. This arrangement prevents false registrations from arising due to the registration of the hundreds digit of one calling line and the tens and/or units digit of another calling line as a calling line number. Components employed.-The individual glow discharge tubes LIT are such that when an ignition potential is applied to the starter electrode the starter gap alone fires and the glow  discharge spreads to the adjacent first marking cathode gap and ionizes it, thus priming this gap. If this cathode then receives a negative impulse, its gap will be fired and the glow discharge will ionize the next gap. Thus the marker cathode gaps may be fired only in the correct sequence (right to left). The tubes A, B, and C are trochotrons and are employed to impulse cyclically the marker cathodes of the hundreds, tens, and units digits respectively of all the lines. Each of these tubes is such that an electron beam scans the receiving electrodes, e.g. 110-119, cyclically and continuously, provided no tube LIT is fired. However, when a tube LIT has fired its starter gap, then the next time the beam in tube A impinges on the electrode connected to the right-hand marker cathode of that tube the marker cathode gap is fired and the low impedance path over that gap causes the beam to remain on that electrode. Operation.-It is assumed that the subscriber Ab has the number 342. When he calls, the resulting drop in potential of his b wire fires the starter gap of his tube LIT and when the beam in tube. A next reaches electrode 113 (connected to the right-hand marker cathodes of all lines having the hundreds digit 3) that marker cathode gap of the calling line tube is fired. Relay A3 pulls up and registers the hundreds digit 3. In a similar manner the tubes B and C are set when the beams reach electrodes 214 and 312 respectively and the remaining gaps of the calling line tube LIT are fired in turn, bringing up B4 and C2. The calling line number thus registered may be used to control in known manner the association of a link circuit and a register. Release of equipment.-When the numberregistering relays operate, relay R1 pulls up connecting leads 15, 16 (each connected to a register) to relays R3, R4 respectively. When the subscriber has been connected to a free register, a voltage sufficient to extinguish the starter gap in the tube LIT is applied to the c wire, and the relevant lead 15 or 16 is connected to positive battery thus operating R3 or R4 and R5 or R6 respectively. Relay NK1 pulls up so that tube LIT is extinguished, and the number-registering relays release, followed by R1. Relays R3 or R4, and NK1 release and the apparatus is ready to deal with another call. Timed release.-If busy conditions are encounted in the switch train, or a defect occurs in the marker, forced release of the identification equipment takes place. When the numberregistering relays operate, a circuit is completed for. R2 which operates after a suitable delay. This operates NK1 as above and transmits a positive impulse via condenser 27 to the blocking tubes BLT (glow diodes) of all lines. Only the tube of the calling line fires and it remains conducting over the calling loop thus transmitting busv tone from Su to the caller. As long as BLT is fired, the cathode of LIT is maintained at a potential sufficiently high to prevent LIT being fired. BLT is extinguished when the caller hangs up. Under permanent loop conditions a negative pulse is reverted on the b wire to fire BLT and initiate release of the identification equipment. Modifications.-The trochotrons may be replaced by relay chains or the like which cyclically apply negative pulses to the marker cathodes.