Patent GB-986232-A (GB)
Title: Improvements relating to traffic signalling systems
Inventor: SHAND GEORGE
IPC: G08G1/09
Filed: 1962-04-18
Abstract: 986,232. Road traffic signals; electric selective signalling systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. March 29, 1963 [April 18, 1962], No. 15117/62. Headings G4H and G4Q. A traffic signalling system, Fig. 1, comprises a number of relays LRI. . . LRN for successive signal locations, each relay, other than the last having a first coil Se in a series connection and a second Se in a shunt connection; and a local switch SWI. . . associated with each location to connect a power supply to cause operation of the location relay and also the relays for a number of preceding locations, means being provided in the circuit for preventing the operation of relays at succeeding locations. The series and shunt relay windings constitute an artificial line which is terminated at the first location by its characteristic impedance. Closure of switch SWX for example connects the local battery to relay LRX which operates to energize an indicator SGX to give a warning of a traffic hazard such as fog, ice, or accident. Current from the battery is also fed back down the line to cause operation of the indicators at a predetermined number of preceding locations, the number of locations being determined by the characteristics of the circuit. Diodes, e.g. RfX in the linking circuit prevent operation of the indicators at succeeding locations. The indicators may be of the type which are only energized during a transition period, such as rotating disc or as is described in Specification 961,091. With such a system a cancelling circuit similar to energizing circuit of Fig. 1 is also provided. One location of such a system is shown in Fig. 3. Operation of the signal initiating button DPB energizes local relay DLR and the similar preceding relays. Operation of DLR energizes repeater relay DLRP which locks in and connect the supply to the "display" contact of the indicator SGA. When the indicator has moved into its display position limit switch DLA opens and releases relay DLRP and disconnects the supply from the indicator. Operation of the "cancel" button NPB similarly energizes relay NLR and repeater relay NLRP to cause the indicator to return to its inoperative state when limit switch NLA opens to release relay NLRP. Alarms may be initiated from a central control station by means of a number of different tones. The location at which an indication is required to be given is selected by means of a receiver RX, Fig. 2, which responds to a particular frequency transmitted on line T from the central station. This receiver operates relay R to connect receivers RA, RI, RF to the line T, each receiver corresponding to a particular hazard, accident, ice or fog. If a frequency corresponding to receiver RA is now transmitted down the line T, receiver RA responds and operates relay AR which connects to supply to the indicator SGA until limit switch DLA opens. Cancellation of an indication is effected by transmitting the location tone only, since with limit switch NLA closed and relay AR deenergized this connects the supply to the N terminal of indicator SGA. Local indication of accidents may be initiated as before by means of button PB. The central station equipment may be of the type described in Specification 986,231.