Patent GB-571047-A (GB)
Title: Improvements relating to remote traffic control systems for railways and the like
IPC: B61L7/08
Filed: 1942-10-20
Abstract: 571,047. Railway traffic control systems. TOMLINSON, A. V. (Union Switch & Signal Co.). Oct. 20, 1942, No. 14680. [Class 105] The invention relates to central traffic control (C.T.C.) systems for railways of the kind in which the telephones, C.T.C. system and dispatcher's call selectors use the same line and is described with parficuar reference to impulse code apparatus of the kind described in Specification 415,787, which may provide a normally open bridged circuit with sources of current at the office and each station, or as shown,' a normally closed line circuit with a source at the office only, the drawings given being based, with necessary modifications, on Fig. 10 of the prior Specification. Such relays as are shown but hot referred to function in the same way as similarly designated relays of the prior Specification. In such systems telephone call selector code transmitters comprising manually operated code wheels, are provided at the office and stations as well as at other points along the track and the initiation of a code at any one locks out the others, selec-. tor codes having priority over C.T.C. codes when two or more codes are initiated simultaneously, a lamp being provided to warn a selector operator against releasing a code wheel when the line is in use by the C.T.C. system and the selector transmitter does not, in consequence, have access to the line. The invention provides that a selector transmitter may be operated at any time, the operation temporarily disconnecting the C.T.C. source from the line. Any C.T.C. code which may be thus interrupted is stored and retransmitted from the beginning, as spon as the line becomes free. the arrangements for interrupting the C.T.C system comprise a distinctive frequency which does not interfere with voice frequencies or selector codes. The drawings show line wires Y. Z which extend along the track and to which the battery 80 is connected over a back contact of the F relay at the office, Fig. 1, the connection including also back contact of office transmitter relay OT, the windings of line relay OR and a low-pass' filter 8, Fig. 1 (continued) shows one field station. Others would be similarly connected. The circuit passes through the windings of station line relay Rand back contacts of master relay M and is completed by a low resistance reactive connection comprising the secondary winding of a transformer 20 at the train dispatcher's office. With relay F released, C.T.C. control code is transmitted by operation of relay OT, and indication code by operation of station relay T in known manner. Wires Y, Z also provide channel for terminal telephones 9, or at dispatcher's office or other point such as SS at which a telephone may be connected to line through jack 77 in answer to call from associated selector 72, each such selector being responsive to a different code transmitter from dispatcher's office. The code transmitting apparatus comprises connector relay 86 picked up during operation of a code wheel 89 by impulses from source B, C over contact 96 and wheel 89, and a pole-changing relay 87 for transmitting alternate impulses of opposite polarity from battery 85 according to the arrangement of code-wheel teeth. Transformer 20 isolates batteries 80, 85 and prevents current from battery 85 from passing through the selector windings. Relay F repeats relay 86 and disconnects battery 80 from the line when a selector code is being transmitted. Relay F is picked up by alternating current from a source BX, CX, passed to the line through transformer 30, its tuned secondary circuit including coil 31 condenser 32, contacts of relay 86 and windings of transformer 20. This current passes through relay R and back contacts of relay M at each intervening C.T.C. station, or through by-pass condenser 11 if relay M is picked up, and passes from line through a tuned filter circuit comprising coil 34, condensers 35, 36, transformer 33, and through amplifier A to relay F. Should the pick up of relay F interrupt a C.T.C. code, station relay R sending the code will be released, and being of biased polar type, will respond only to alternate impulses of the selector code which follows the interrupted C.T.C. code, and so will be released most of the time, and particularly for a relatively long period at the beginning of the selector code. Starting relay ST which initiated the C.T.C. code remains picked up. When the line becomes steadily reenergized from battery 80 at the end of the selector code relays L1, L2 become released at the same time to permit relay ST to complete circuit for relay M to initiate a new code. In Specification 415,787 an interrupted code is repeated if the interruption occurs during steps 1 to 8 of the 16-step code. In the present case, in order that repetition shall occur if the interruption is on any of the 16 steps, each office starting relay such as 234, Fig. 1 (Fig. 5 of prior Specification) has a back contact of relay 016 included in its holding circuit, and a back contact of associated selector relay 234S included in the station code call circuit with contact c of relay 234. With respect to current-for control of relay F, source BX, CX is described as providing 60 cycle A.C. and transformer 30 is adjusted so that the corresponding line current is of such low value as to be practically inaudible in telephones 9 and far below the minimum to which selectors 72 and relay R are responsive. Amplifier A, Fig. 1 is therefore interposed to render relay F responsive to this line current, the amplifying arrangement, Fig. 2, comprising an electron tube of controlled ionization or "cold cathode" type, the direct current neutral relay F, in parallel with a condenser 39, being connected in series with the secondary winding of transformer 37 across the anode and cathode of the tube, the primary of the transformer being supplied with alternating current of voltage insufficient to start ionization of the tube to render it conductive. The secondary of transformer 33 is connected to the control element 38 so that when the primary receives the line current through the filter circuit shown which makes the arrangement selectively responsive, potential of proper polarity applied to element 38 starts ionization and renders the tube conductive. During alternate half-cycles the condenser 39 is therefore charged and relay F energized, the relay being retained energized during the intermediate halfcycles by discharge of the condenser. The Specification also indicates the kind of modification needed for the situation of the dispatcher's office to differ from that shown, and for application of the invention to a normally open line circuit.