Patent GB-632605-A (GB)
Title: Improvements relating to remote control systems
IPC: B61L7/08
Filed: 1947-07-30
Abstract: 632,605. Electric selective signalling. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. July 30, 1947, No. 20658. Convention date, March 28, 1940. [Class 40 (i)] In a remote control system comprising an office and a plurality of stations connected by two line wires normally energized from the office, a line relay at each station is shunted across the line, and the code transmitter at each station, when operated, connects the line wires together periodically to deliver a multiple impulse code thereto to operate selectively responsive means at the office, the line relay at the operative station also being operated in accordance with the code and governing the operation of the associated code transmitter. The invention is an improvement on that disclosed in Specification 629,984 and provides an improved centralized-traffic control system of the code type described in Specification 415,787 wherein existing line wires provided, e.g. for telephone and telegraph communication, are used. Telephony and telegraphy arrangements, Fig. 1. The line wires Y, Z, primarily provide a telephone circuit arranged for train despatching purposes, extending from the despatcher's office to another main office, the telephoneapparatus 5 at each end of the line being connected thereto over a transformer 3 and condensers 2. A known telephone call selector system using code wheels 89 is also provided at thedespatcher's office to call selectively various similar way stations. Each of these selector stations, one only being shown, comprises a selector 72 shunted across the line YZ for selectively operating a call-bell 76, the operator at a called station connecting his telephone to the line by means of the jack 77. The selector system and the C.T.C. system are so arranged that only one system can obtain control of the line at a time in a manner somewhat similar to that disclosed in Specification 629,984. The line YZ is " simplexed " in the usual manner by choke coils 7 and resistors 8, 9 at each end to provide a duplex telegraph circuit extending from ground at each end through standard terminal apparatus B1, N1, PC1, R1, AL. The line wires YZ in multiple may also be used as one side of a further " phantom " telephone circuit by means of jacks 6 connected to the mid-points of the condensers 2. C.T.C. system. The office of the C.T.C. system is assumed to be located at the despatcher's office and the various field stations 357, 358, 246, &c. are located at various points along the line, only one being shown in any detail. The C.T.C. system functions as described in Specification 415,787, except for the following. C.T.C. office arrangements. The office line relay OR, of the polar stick type, is normally de-energized but the line YZ is normally energized from the battery 80 at the office over contacts 14, 15 of a line polarity reversing . relay PC, contacts of a connecting relay 86 which determines whether the C.T.C. or the selector system controls the line, and a low-pass filter network 12. During transmission of control codes by relay OT the office master relay OM short-circuits the upper winding of line relay OR so preventing operation thereof by line pulses over the transformer 4. The line relay is then controlled locally over its lower winding by interaction with OT in accordance with the control code and functions as in Specification 415,787 except that in the event of a break in the line, in the present system, the control code transmission continues out to the location of the break. Transmission of an indication code from a field station is effected as described below by increasing the line current periodically, these current changes actuating the office line relay OR through transformer 4. The line current increases reverse the line relay contact 24 from its normal position shown, the decreases in line current returning the line relay to normal. When relay OR reverses on receipt of the first line impulse of an indication code its contact 24 connects battery to line 18 to initiate sequential operation of the timing relays OL1, OL2 ... and operates the reversing relay PC to reverse the line current polarity. Relay PC operates a delayed relay PCP to energize momentarily the local (lower) winding of line relay OR so that any change in the primary current of transformer 4 as the line current polarity reverses will not affect relay OR. Line relay OR operates as in the prior Specification in unison with the operative field station line relay to control the office coding unit in the usual manner. The reversing relay PC remains' energized until relay 016 energizes at the end of the code transmission, when the line polarity is again returned to normal,' this change having no effect on line relay OR as its upper winding is shunted by contact 38 of relay 016. Relay PCP is de-energized as PC releases but delivers another pulse to the local winding of line relay OR before falling off, further to ensure that relay OR remains in its normal position. Field station; operation. The line relay R at each field station is normally energized from the line YZ through the low-pass filter network 12 and functions as in Specification 415,787 in response to control codes from the office. Transmission of an indication code by a field station is, as in the prior Specification, effected by a start relay ST which energizes the master relay M and the transmitter relay T in turn. Relay M releases the line relay R and shunts the line YZ to release the line relays R at remoter C.T.C. stations, thereby preventing any signal transmission therefrom. Relay T shunts the line YZ by a low-impedance path comprising the filter coils 12 to increase the line current from the office to the operative field stationthe first code step. The consequential reversal of the line current polarity by reversing relay PC as above described releases the line relays at the nearer field stations, relay T then functioning to control its associated line relay R in unison with the office line relay OR in the usual manner. Interference ; preventing. Should the office initiate a control code at the same time as an indication code is initiated by a field station, the operation of the office transmitter relay OT causes relay E at the operative station to energize and stop further transmission from the station and condition the station for reception of the control code. Should two or more stations initiate indication codes simultaneously they continue in operation as long as the code elements are alike but when a difference occurs one or another is locked out, a long odd-numbered code step taking precedence over a short one and vice versa for even numbered steps. By arranging the code calls of the stations according to their geographic location a nearer station may always have precedence in such cases of simultaneous initiation of indication codes. Telephone selector and C.T.C. office, selective control. To call a selector station the corre. sponding code wheel 89 is wound up and released, whereupon it makes one revolution during which the connecting relay 86 connects a D.C. source derived from a rectifier 47 to line YZ in lieu of the battery 80. Impulses of alternating polarity are fed from this source by the polarity reversing relay 87 in accordance with the code-wheel teeth. The selector call apparatus may be operated only if the C.T.C. apparatus is at normal ; since the circuit of relay 86 is made over a normally closed contact 46 of relay OLBP. The relay 86 locks until the code wheel rotation is completed, and energizes the filament circuit of the rectifier 47. To permit this valve time to warm up, each selector code starts with a long " line-open " period which is effective also to lock out any field station that happens to initiate a code at the time. Relay 86 also reverses the C.T.C. office line relay OR for the duration of the selector code to prevent initiation of a control code until the selector code is completed. The selector and C.T.C. codes are mutually non- interfering in respect of the receiving apparatus because of the difference in the relative proportion of long and short code elements. Modifications. The office line relay OR may be of the biassed polar type similar to the station line relays R, Fig. 2 (not shown). Twoway repeater stations, Fig. 3 (not shown), may be used to extend the transmission distance or where there is a break in the line wires YZ. In another form of the invention the office line relay OR, Fig. 4, is normally energized from the remote end of the line by a supply BX1, CX1 at supersonic frequency f<SP>1</SP> (to prevent interference with line telephone currents), through a tuned filter 81, amplifier A and rectifier 84. Control codes are transmitted from the office in the usual manner by periodically disconnecting battery 80 from line, but can be initiated only when the line is free and available throughout its entire length. During transmission of an indication code from a station the line is periodically shunted by the bridge 78, C1 tuned to frequency f<SP>1</SP> so that the code impulses sent to the office are A.C. trains at this frequency to which the office line relay OR responds. The relay OR at its contact b transmits a battery code in the opposite direction which as heretofore not only operates the line relay R at the transmitting station in unison therewith to govern the indication code transmission, but also effects locking out of remoter stations which may initiate an indication code at the same time. In a modification, Fig. 5 (not shown), A.C. pulse trains are used for signalling in both directions. The office line relay, as in Fig. 4, is normally energized through selective filters and a rectifier from the source f<SP>1</SP> located at the remote end of the line. The office battery is replaced by two A.C. sources of frequencies f<SP>2</SP>, f<SP>3</SP>. Normally the source f<SP>2</SP> is connected to line to energize the stat