Patent GB-788591-A (GB)
Title: Improvements in or relating to cold cathode gas filled electric discharge tubes
Inventor: BECK ARNOLD HUGH WILLIAM
IPC: H03K17/52
Filed: 1953-09-02
Abstract: 788,591. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 2, 1953, No. 24260/53. Addition to 734,345,.[Group XL (a)]. Class 40 (4). [Also in Group XL (a)] A switching circuit for connecting any one of ten inlets to any one of three outlets, and similar to circuits described in Specification 788,592, comprises a pair. of cold cathode gas-filled discharge tubes 14 and 14<SP>1</SP>; 15 and 151 or 16 and 161 associated with each outlet. Each tube (see Group XL. (a)), for example tube 14, comprises ten individual anodes A1 to A10 separated by screens (not shown) and a single anode a1, which may comprise ten individual anodes commoned together, associated with a cold cathode K1. A speech transmission path is established between any one anode A1 to A10 and anode a1 by establishing discharges to these anodes from the common cathode K1, as described in Specification 734,345, [Group XL (a)]. The secondary winding of transformer T1 associated with inlet 1 is connected between anodes A1 and A1<SP>1</SP> of tubes 14 and 14<SP>1</SP>; similarly, inlet 2 is connected between.anodes A2 and A2<SP>1</SP> and so on. Corresponding anodes A1, B1, C1; A2; B2, C2, &c. of the tubes are connected together so that each, inlet is multipled to corresponding anodes of each of the three pairs of tubes associated with the three outlets. The centre point of the secondary winding of each inlet transformer T1 is connected to a respective resistor R1 and thence to ground through a rectifier W1, and the junction point between each resistor R1 and rectifier W1 is connected through a resistor R2 to a respective pulse terminal 17. to 26. The high impedance windings of the outlet transformers T2 are connected between the anodes a1, a1<SP>1</SP>; a2, a2<SP>1</SP> and a3, a3<SP>1</SP> and the centre point of each winding is connected to ground through a resistor R conveniently of the same value as resistor R1. The cathodes K1, K1<SP>1</SP>; K2, K2<SP>1</SP> and K3, K3<SP>1</SP> are connected together through a respective centre-tapped choke L, each centre tap being connected through a rescistor R3 and rectifier W2 to a negative supply terminal 27. The junction point between each resistor R3 and rectifier W2 is connected through a resistor R4 to a respective pulse terminal 28, 29 or 30. Negative going 250 volt pulses PM1, PM2 and PM3 of say 100 milliseconds duration are applied repetitively in succession to the respective terminals 28, 29 and 30, and during each pulse PM 50-volt positive pulses PL1 to PL10 of say 10 milliseconds duration are applied in succession to the respective terminals 17 to 26. The terminals 27 are connected to a 200-volt source of negative potential which is sufficient to maintain a discharge in any of the tubes but insufficient to initiate a discharge, a striking voltage of the order of 300 volts being required. Thus the pulse PM1 applied to terminal 28 every 300 milliseconds will not alone cause tubes 14 and 141 to fire, but if during the time interval in which the pulse PM1 is applied a pulse PL1 is applied to terminal 17, the tubes 14 and 14<SP>1</SP> fire and a connection is established between inlet 1 and outlet 1. The discharge current flowing through rectifier W1 of inlet 1 renders inoperative any further application of the pulses PL1, while the current flowing through rectifier W2 of outlet 1 renders inoperative the subsequent pulses PM1 applied to terminal 28. The voltage drop across resistor R can be used for monitoring or other control purposes if desired. Tubes 14 and 14<SP>1</SP> and outlet 1 have thus been seized by inlet 1. In the same way outlets 2 and 3 may be seized by any of inlets 1 to 10. An engaged connection is disconnected by reducing the supply voltage at the appropriate terminal 27 to a value below that needed for maintenance of discharge in the associated pair of tubes. On re-establishment of the normal supply voltage the outlet is rendered accessible to any disengaged inlet.