Patent GB-596994-A (GB)
Title: Improvements relating to remote control systems
IPC: B61L7/08
Filed: 1945-05-31
Abstract: 596,994. Electric selective signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. May 31, 1945, No. 13684. Convention date, Sept. 9, 1944. [Class 40 (i)] In a remote control system, e.g. for centralised railway traffic control, in which codes formed from an invariable number of long and short marking and spacing elements, as described in Specification 415,787, are sent from an office to field stations and vice versa, the transmission system includes a wired or wireless carrier link, which employs a single carrier frequency for code signalling in both directions. The carrier link may be between the office, Fig. 1A, and a repeater station, Figs. 1B or 2B or between first and second repeater stations, Figs. 2A and 1B or 2B. If codes are initiated simultaneously at both ends of the carrier link, the office code is given priority. Transmission and reception of control codes :-A control code is initiated by the operation of master relay OM, Fig. 1A, which connects the office transmitting relay OT to a coding unit CU. Relay OT controls relay OR, which controls timing relays in the coding unit, and these relays in turn control OT. Relay OT and its repeater relay TC operate. in accordance with the code and intermittently connect oscillator OSC to antenna A. These radio signals are received by antenna A1, Fig. 1B, and applied to a relay 1CR, which repeats them by intermittently replacing a battery B1 normally connected to line wires Y1-Z1 by a resistance ; relays R at the field stations respond. Relay OL1; OL2 ; OLB ; OLBP O16; PC ; PCP are used for timing the code elements in the manner described in Specification 589,332. The first half of the code conditions a particular field station coding unit to receive the second half of the code which operates signals &c. In a modification, Fig. 2A, the office is connected via line Y-Z, over which field stations are controlled by D.C. codes as described in Specification 589,332, to a first repeater station where biassed relay PR, operating in accordance with a code transmitted by relay OT, converts the D.C. codes into radio signals by intermittently connecting oscillator OSC to an antenna A. The codes are received by antenna A1 and transmitted to the field station receiving relays R, as previously described. In a further modification, Fig. 2B, the operation of relay 1CR transmits a control code received from antenna A, Fig. 1A or 2A, to the field station receiving relays R located along two lines Y1-Z1, Y2-Z2. This arrangement allows the repeater station to be situated at any point in the controlled territory. Transmission and reception of indication codes.-When a field station device operates, e.g. due to the passing of a train, a master relay M, Fig. 1B, operates and connects the field stations transmitting relay T to a coding unit CU, relay T repeats the code by periodically shortcircuiting the line relay R, so that the current in line Y1-Z1 is periodically increased. A change in line current produces an E.M.F. in the secondary of transformer 40, which is applied to a relay IR of the magnetic stick type. When relay IR operates, relay IPC is energized and reverses the polarity of the line as required for the intermittent operation of the receiving relay R, which must operate before each successive code element can be produced; at the same time, change of line polarity causes the release of the receiving relays R at the other field station on the line, thus preventing code interference. If relay ICR has not been operated, due to a control code, directional relay Z now closes a circuit for relay ITC. Relay ITC operates in unison with relay 1R, and periodically connects oscillator OSC to antenna A1. These radio signals are received by antenna A, and applied to office receiving relay OR, which repeats the signals into the coding unit CU. The first element of a code as transmitted by the repeater station, is shorter than the first element transmitted by relay T so that relay TS holds the receiving relay OR reversed for the correct period of time. The first half of the code received by the coding unit selects a panel corresponding to the field station from where the code originated and the second half operates a graphic recorder which indicates the conditions of the field station devices. In order to minimize the time interval between successive codes, the coding units at the remainder of the field stations which are rendered ineffective during the code transmission, are restored to normal at the end of an indication code by the transmission of a single code element from the office. In the system shown in Fig. 2A, a code transmitted from antenna A1 in the form of radio signals is received by antenna A and applied to relay CR which intermittently shortcircuits resistance 20 in accordance with the code. When resistance 20 is short-circuited, the current in line Y-Z and in the primary of transformer 40 is increased and thus an E.M.F. is induced in the secondary of transformer 40, which is applied to the office receiving relay OR. Relay OR operates the coding unit CU in accordance with the code and simultaneously operates relay CP which changes the line polarity of line Y-Z each time relay OR operates. The restoration of line polarity to normal at the end of a code causes relay NR, which is energized when the line polarity is reversed, to release, thereby de-energizing a slow release relay NP which is held energized by relay NR throughout the code. When relay NP is de-energized, relay TC is momentarily operated to send out the first element of a control code, which immediately restores the field stations to the receiving condition. In the modification in which the field stations are located on two lines Y1-Z1, Y2-Z2, each connected to a repeater station, Fig. 2B, relay 1R receives codes transmitted along line Y1-Z1 and relay 2R receives the code transmitted along line Y2-Z2. When relay 1R or 2R operates, relay ITC operates in unison so that a code is transmitted by antenna A1 as previously described. Preventing interference of codes ; priorities.- When a plurality of codes are initiated simultaneously, the code transmitting the first " long " element receives transmission priority. The first element of a control code is "long" and that of an indication code "short," so that a control code always has priority. On the reception at the office of a " long " element of an indication code, either relay OL1 or OL2, Fig. 1A, is released, depending on whether the element is an odd numbered or even numbered one, and thereby disconnecting the control code initiating relay OM from its pick-up circuit. On the reception at a field station of a "long" code element, relay E operates, completes a holding circuit for itself, for the duration of the code and at the same time opens the pick-up circuit of the indication code initiating relay M. If a field station, which had previously started to transmit an indication code, but has not sent out a "long" element, receives the first element of a control code, then the indication code is terminated and the field station restored to the receiving condition. The first element of a code transmitted by a field station along line Y1-Z1, Fig. 2B, changes the line polarity by operating relay 1PC and thereby dissociates the rest of the field stations from the line until the code has been completed. Relay 1PC also prevents field stations on line Y2-Z2 from transmitting a code by disconnecting the current supply therefrom. Relay 2PC, controlled by field stations on line Y2-Z2, carries out the same function as relay 1PC. When relays 1PC, 2PC operate simultaneously, due to code transmission along both lines Y1-Z1, Y2-Z2, the station on line Y1-Z1 receives priority, since when relay 1PC operates, it opens circuits relay 2PC. Fault conditions.-If the operation of the office receiving relay OR is terminated before a complete indication code is received, e.g. due to a fault, then a timing relay OLBP operates and connects the control code, transmitting relay OT to the supply, so that it transmits a single code element which restores the system to normal. To prevent interference due to a fault, a field station can be disconnected from the system by depressing, at the office, a pushbutton switch PB, Figs. 1A, 2A, when the field station is transmitting an indication code. Relay R at the particular field station is the only receiving relay which is in a condition to receive a code so that when switch PB is depressed for a period of time greater than the length of a code, relay TC is energized and a corresponding signal is transmitted by antenna A to the receiving relay R which responds accordingly and disconnects the field station from the line.