Patent GB-735635-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: DAVISON ALAN
IPC: H04Q3/52
Filed: 1951-12-14
Abstract: 735,635. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Nov. 10, 1952 [Dec. 14, 1951], No. 29313/51. Class 40 (4). Register circuits are provided in common to all subscribers' lines and each line has associated therewith a plurality of sets of gas discharge tubes equal in number to the number of register circuits, a connection between a calling and a called line being effected by the striking of a set of tubes associated with each line and serving to connect the two lines to the same register circuit. The invention is illustrated schematically in Fig. 1 as applied to a 100-line exchange. Registers shown and referred to as link circuits 1-10 control the setting up and supervising of a connection. A common control unit CC includes a circuit for allotting.idle links for use in turn and includes a continuously operating scanning arrangement which tests all the lines in the system successively. When a calling line, say 01, is found the scanner stops and a set of tubes O1T1 associated with the preselected link circuit, say link 1, strike to extend the calling line to the link circuit. Dialling tone is returned and the calling party dials the 2-digit number of the required line. When the digits are stored in the link circuit, the common control unit CC is taken into use again and is controlled by the digits to strike the tubes of the set, say 99T1, associated with the wanted line 99 and with the link circuit 1 to complete the connection. Detailed circuit. The system includes a number of counting chains of the type in which only'one tube at a time fires, extinguishing the previously fired tube and priming the next. A 400 p.p.s. supply from multivibrator VT13, VT14, Fig. 5, produces outputs PS1-PS3 of different amplitudes from tubes VT15, VT16. Line finder. A scanning device consists of outgoing tens and units marking counters OTMC, Fig. 3, and OUMC, Fig. 6, and a set of outgoing units marking pulse tubes OUMP. The cathodes of the tubes of OTMC and OUMP are connected over leads such as TL1 and UL1 to line circuits having corresponding tens and units digits. When one of the tubes in OUMC conducts it causes'the corresponding tube in OUMP to fire at the next PS1 pulse, extinguishing again at the end of the pulse. The home position tube VK94 in OUMP controls the tens marking counter which marks one tens digit while OUMP goes through one cycle. Thus, all the line circuits are marked in turn. Normally the voltage applied over a lead such as UL1 is insufficient to fire tube VK11 in a subscriber's line circuit SLC. However, when the subscriber closes his loop, the voltage through impedance 10 becomes less negative to prime VK11 so that a pulse on lead UL1 fires the tube for the duration of one pulse. If the tube VK12 is also primed by the corresponding tube VK34-VK43 in the tens marking counter OTMC, VK11 fires VK12. VK12 is selfextinguishing and repeats the pulse to all the OP tubes VK16 associated with the calling line. That tube VK16 primed by the allotter bias lead AB strikes and fires the speaking path tubes VK14, VK15 in the same set. VK12 also fires VG2 which strikes tube VK31 in the line finder stop circuit LFS. VK31 fires VG6 to cause the stop tubes VT2, Fig. 3, and VT17, Fig. 5, to conduct so extinguishing the tubes in the tens and units marking counters OTMC and OUMC to stop the scanning. VK31 also applies a " Z " pulse to the striking electrodes of tubes such as VK122, Fig. 6, in all link circuits, that tube VK122 primed over allotter bias lead AB striking. Preselection of link circuit by allotter. VK122 is self-extinguishing and acts as a pulse repeater to strike VK199, Fig. 6, in the sequence control circuit SCC, so dowsing the normallyconducting tube VK118. The allotter now pulses lead AS to preselect the next idle link circuit. VG20 in the link circuit corresponding to the conducting tube such as VK75-VK84 in the allotter circuit conducts only if VK118 is conducting, an indication that the link circuit is idle. When VG20 fires it operates VT19 in the step allotter circuit SAC, Fig. 5. VT19 cuts off VG17, VG18, VT20 and strikes VK87, which fires VK127 in the timing and reset circuit TRC, Fig. 6, the normally-conducting VK126 extinguishing. As previously described, when the link is taken into use, VK122 and VK119 strike and VK118 is extinguished so that VT19 is cut off and VG17 strikes, causing VK86 in SAC to repeat PSI pulses to the allotter which hunts with VK75-VK84 conducting in turn until an idle link circuit is found when the allotter stops with the appropriate tube VK75-V84 conducting. At the preselection of a link, when VK127 strikes it causes VK92, VK93, Fig. 5, to fire at the next PSI pulse. VK92 marks lead AD to strike VG7 in the line finder stop circuit LFS to make VT1 conduct. VT1 extinguishes VK31 but stop tubes VT2, VT17 remain conducting to disable the tens and units marking counters OTMC, OUMC to prevent scanning until the allotter has preselected another link circuit. Successive PS1 pulses operate succeeding tubes in the timing and reset circuit TRC. When VK125 strikes, VG23 fires so that VT22 conducts to extinguish VK92, whereupon VT1, VT2, VT17 cut off if by this time the allotter has found an idle link. Finally, VK126 strikes to the next PS1 pulse to extinguish VK125, VG23 and VT22 so that the common equipment is restored to normal and scanning restarts. Dialling tone. A v.f. source of 400 c.p.s. is connected over lead VF to all subscriber's lines over C1 and R2, Fig. 3. Normally, rectifier MR5 is biased to non-conducting but when a line is looped and the line is connected to the link circuit, the v.f. current flows through MR5 and tubes VG4, VK16 and the primary of transformer TR3, Fig. 4. The current in the secondary is amplified by VT6, rectified and doubled by D1 and applied to VT8, which extinguishes VK44, VT9. VK45, VK46 thus strike and mark leads AP, CP. Tubes VK51, Fig. 4, and VK130, Fig. 7, primed from VK119 at seizure of the link, now fire and prime the first tubes VK52, VK131 in the incoming tens and units marking counters ITMC, IUMC. The potential on lead CP fires VK153 in the sequence control circuit SCC to extinguish VK119 and strike VG11, Fig. 4, over lead DA to cause dialling tone from lead DT to be applied through VG11, VT7 and transformer TR2 to the calling line. Registration of dialled digits. The calling party dials the 2-digit number of the wanted subscriber. The first break interrupts the v.f. current over the OP lead to cut off VT8, Fig. 4, but the striking electrode of VK44 is controlled by a delay network so that VK44 cannot fire during the break period of an impulse. However, VT9 conducts during break periods and extinguishes VK45, VK46. At each make VT8 conducts again, cutting off VT9 so that VK45 fires and pulses lead AP to strike VK50, which registers the pulses in the incoming tens marking counter ITMC. VK46 is also controlled by a delay network so that after the first break it remains extinguished only at the end of the first digit. Thus VK45, VK44, VK46 perform the functions of A, B, C relays, respectively. When VK46 strikes it marks lead CP to strike VK154 in SCC, which' extinguishes VK153, VK50, VG11 and primes VK129 so that the second digit is registered in the incoming units marking counter IUMC. At the end of the second digit a further pulse over lead CP fires VK155 in SCC to extinguish VK154 and strike VG24. Selection of called line. As soon as the common control circuit CC is available again and scans the calling line so that the related tube VK95 in OUMP strikes again, VK163, Fig. 7, primed by VG24 strikes to fire VK164 primed from VK33 in OTMC. VK164 primes the IP and D tubes VK17, VK18 of all the sets of tubes connected to the link circuit, i.e. O1T1-99T1. VK164 fires VG31, Fig. 7, to strike VK88 to start the timing reset circuit TRC, Fig. 5, and fires VK184 in the allotter. VK164 also fires VG30 to operate stop tubes VT2, VT17 to interrupt scanning. VK184 operates VG21 and VT19 to cut off stepping pulses to the allotter. VK184 also causes VK29, Fig. 3, in the incoming mark circuit ICM to strike at the next PS1 pulse. VK88 causes VK89-VK93 and VK123-VK126 in TRC to fire to successive PS1 pulses. VK120 causes VK165 to apply a pulse to all the tubes in the incoming tens and units marking tube transfer chains ITMT, IUMT to strike that tube in each chain primed by the associated counter ITMC, IUMC, respectively. The units digit marking is extended from IUMT to fire the corresponding tube VK19-VK28 in ICM when VK29, Fig. 3, fires as mentioned above. The tube VK19, say, strikes all tubes such as VG3 in all the line circuits having the same units digit as the wanted line, to pulse the striking electrode of the related tubes VK12 but only that tube VK12 primed by the tens digit through ITMT strikes, assuming that the required line is idle. VK12 fires VK31 through VG2 to operate the stop tubes in the line finder circuit. VK31 sends a " Z " pulse to the link circuit to fire VK162 which strikes VK157 in the sequence control circuit. Meanwhile the timing and reset circuit has begun its operation. VK88-VK91 strike in succession, the last at the same time as VK121. Ringing current and tone. VK12 in the called line circuit strikes the IP and D tubes VK16, VK18 relevant to the called line and the link circuit, these tubes drawing current to fire the speech path tubes VK14, VK15. VK18 strikes VK10 to supply ringing current from leads IR to the called line. At the same time VK157 in the sequence control circuit strikes VG13, Fig. 4, which returns ringing tone to the calling party over lead RT and tube VT7. Resumption of call-finding and selecting. Meanwhile VK91 in the timing and reset circuit TRC fires VK92, VK93 at the next PS1 pulse. VK92 strikes VG9, VG19 to operate VT3, Fig. 3, and VT21, Fig. 6, to reset the incoming tens and units marking transfer tubes ITMT, IUMT. VK92 also strikes VG7 to operate VT1 in the line finder st