Patent GB-856148-A (GB)
Title: Electrical selector circuits
IPC: H04Q3/00
Filed: 1958-08-08
Abstract: 856,148. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Aug. 8, 1958 [Aug. 14, 1957 (2)], No. 25497/58. Class 40 (4). In a high-speed hunter in which a plurality of stages, of which each but the last is associated with an outlet, operate in succession in response to a start impulse, and the sequential operation is stopped as soon as a stage associated with an available outlet has been operated, some or all of the stages are subsequently operated to generate a train of pulses indicative of the identity of that available outlet. First embodiment-all trunks available in same order on each demand.- Each of the ten trunks of a group (not shown) is associated with one of the contacts 21 to 30 (Fig. 1), those corresponding to busy trunks being closed to operate the corresponding relays of TK1 to TK10. A demand for a free trunk results in the closure of contacts 22<SP>1</SP>, whereupon the start relay 13 pulls up, grounds terminals C of the gates B1 to B10 (Fig. 3) corresponding to busy trunks, resets the trigger pairs FF1-FF10 and OFL (Fig. 2) via capacitor 20, starts the pulse source 11 and connects it to the set terminal S of FF10. Assuming trunks 1 and 10 to be busy, the gates B1 and B10 will be enabled. Source 11 delivers a single positive pulse to FF10, thus triggering it to its high current condition so that the output terminal which is normally at- 18 volts becomes less negative. This relatively positive potential passes via B10 to set FF9, which resets FF10 via its terminal R, and enables the gate C9 (Fig. 4), B9 being blocked. The trunk associated with stage S9, i.e. trunk No. 9, is thus chosen. On the relapse of armature 22<SP>1</SP>, relay 13 falls away, thus disabling B10 and B1, and allowing pulses from the continuouslyrunning source 12 to pass via gate 14 (Fig. 5) to inputs of C1 to C10 and to the output circuit 15. Gate C9 is enabled (FF9 set) and consequently the first pulse passes via C9 to set FF8, and to the output circuit 15. FF8 resets FF9 and enables C8, so that the second pulse passes via C8 to set FF7. The remaining stages operate sequentially in like manner, stages S8 to S1 controlling the sending of eight pulses and OFL that of the ninth. With OFL set, the gate 14 is disabled to stop the supply of pulses from source 12. All trunks busy.-In this case all the gates B1 to B10 are enabled and FF10 to FF1 are operated in succession, followed by OFL which gives an overflow indication to the output circuit 15 over a front contact of relay 13. Second embodiment-different trunks available in differing order for different demands.-In Figs. 6-8 which illustrate this embodiment, a normally closed (break) contact of a relay is shown as a single short line perpendicular to a conductor, and a normally open (make) contact as an X crossing the conductor. There are eleven stages SO-S9 and OFL, of which S0 S1, S9, and OFL only are shown. Each of the ten trunks in the group is associated with one of the contacts TR0 to TR9, the contact being normal (closed) when the trunk is idle, and open when it is busy. The ten demand contacts 201 to 291 are respectively associated with ten requesting sources, and closure of one of these contacts together with that of the start contacts ST of a start relay (not shown) initiates a hunt. The operated contacts bring up the relay of VG0-VG9 corresponding to the requesting source, which associates six of the ten trunks with the stages S0 to S5 by extending the relevant six leads of TO-T9 to LO-L5, respectively. The operated VG relay enables the gate TSS2 (Fig. 11) thus completing a path from the pulse source 11 to the set terminal of FFO (Fig. 10). Assuming that contact 20<SP>1</SP> is closed, VG0 pulls up and allots T3, T2, T1, T0, T9 and T8 to stages SO to S5, respectively. The gates BO-B9 (Fig. 12) are normally enabled but those associated with busy trunks are now inhibited by ground extended to their C terminals. Assuming trunks T3 to T7, inclusive, to be busy, gates B1 to B5 will be inhibited. The source 11 continuously produces positive pulses at 500 p.p.s. and the first pulse through TSS2 sets FFO, which blocks TSS1 to prevent further pulses passing, and delivers a positive pulse via B0 to set FF1. FF1 resets FFO and passes a positive pulse to the gate-inverter Il (Fig. 13). If FF1 is set and FF0 is reset, 8T (Fig. 13) conducts and delivers an output positive pulse to B1, which is blocked. FF1 therefore remains set. The output terminals of FFO-FF5 are connected to network 18, which under the control of the operated VG relay (VGO) converts the stage identity to the corresponding trunk identity. With FF1 set, positive potential is thus extended over a front VGO contact to operate TSA2 which locks up, indicating that the selected trunk is No. 2. The operation of this relay provides an additional inhibiting ground to TSS1, inhibits all ten gates BO-B9, operates relay TSAK, and enables gates TSR and RI7. Relay TSAK disconnects the relays TSAOTSA9 from network 18, but TSA2 remains locked up. The next pulse from source 11 passes via amplifier TSRA, gates TRI, TCK1 (FF1 set) and amplifier TSRB to the reset terminals CR of TREF, TSK, OFL and FFOFF9, thus inter alia resetting FF1. Gates TCK1 and TCK3 are thereupon disabled, and TCK2 and TCK4 are enabled. The second pulse therefore passes via TCK2 to set TREF, which inhibits TRI and enables THE ; whereupon the third pulse passes through gates TRE and TCK4, and amplifier TRA to the gates RI0-RI9. With RI7 enabled, FF7 is set, thus disabling TCK2 and TCK4 and enabling TCK1 and TCK3, so that the fourth pulse passes from TRE through TCK3 to set TSK which enables the gate TSKA in the outpulsing chain. The next pulse therefore passes via TSKA and the enabled gate CD7 (FF7 set) to set FF8, subsequent pulses setting FF9 and DFL, whereupon OFLA is disabled to prevent further pulses being sent. The pulse train of three pulses sent to the output circuit 15 identifies trunk No. 2 which was selected. All trunks busy.-In this event the relevant six contacts of TRO-TR9 are all operated and all ten gates BO-B9 are enabled. The pulse applied to FF0 therefore causes all ten circuits FFO-FF9 to be set in succession, followed by OFL which operates relay OFLR. With TSAO-TSA9 all normal, this provides an overflow indication to the output circuit 15. Specifications 753,014, 842,130 and 856,147 are referred to.