Abstract: A circuit arrangement for providing in a fail-safe manner an alternating output signal to a load, e.g. in a railway signalling system. The load is connected across a first winding of a transformer, to opposite ends of a second winding of which transformer is connected a bi-directional current switching circuit. First and second modulated signal sources are connected to the bi-directional switching circuit. Each of the signal sources modulates a carrier signal with a modulation signal, the outputs of the signal sources being out of phase with respect to each other. The bi-directional switching circuit is operative to switch current through the second winding alternately in opposite directions at the frequency of the modulation signal. The circuit arrangement is such that if any of its components fails to operate correctly, the output appearing across the first winding is no greater than a threshold level.

Abstract: A railway vehicle control system particularly, but not exclusively, suitable for controlling single track working. Transponders are located at fixed positions along the track such as at intersections, points and so on, and a vehicle is provided with sensors for detecting the transponders. A central control office supplies information concerning an identifying characteristic of the next transponders expected to be detected, when this happens the event triggers apparatus on the vehicle to communicate with the central office which then supplies information to identify the next transponder. The same sequence of events ensues as each successive transponder is passed. The transponders may be staggered alternately to opposite sides of the track for identification purposes. If the expected transponder is not detected but instead a different transponder is encountered, then a vehicle safety function such as the emergency brakes, may be brought into operation.

Abstract: A railway vehicle control system comprises a railway track (1) and a plurality of transponders (N, N+1, N+2) at predetermined positions along the track. A railway vehicle (2) moves along the track, the vehicle having means (20, 21) for detecting each of the transponders. A control location has means (4, 5, 6, 7, 7a) for periodically transmitting vital safety signalling information to the vehicle via a radio link. In response to detection of one of the transponders, the vehicle sends a first message via the link to the control location and in response to reception of the first message by the control location, the vital safety signalling information is sent a first time from the control location to the vehicle via the link, then from the vehicle to the control location via the link and then a second time from the control location to the vehicle via the link.

Abstract: An interlocking system comprising a plurality, e.g., three, of parallel sub-systems operating asynchronously to produce identical replicated outputs which are mutually compared to determine the correct output and disqualifying a minority output thereby ensuring high system integrity. Each sub-system includes a similar arrangement for computing the difference between all possible pairs of sub-systems. Comparison of these results with a reference table of all possible difference results and then comparison of the difference equations yields a common factor which is the sub-system producing the error. Action can then be taken to disqualify its output, e.g., by switching-off its power supply. A final output is taken, preferably from one sub-system, with a second as standby.

Abstract: Vital transmission checking apparatus is disclosed for a communication channel which transmits quasi-static signals representing several alternative states of a function, e.g., the control function for a signal in a railway control system, one of which states is potentially unsafe. Each function channel transmits a digital signature code of predetermined length which is continuously repeated in a selected form, e.g., non-inverted, inverted, or alternately inverted and non-inverted, to represent the different states of the function. To provide a check of proper transmission, the repeated signature code is periodically corrupted in accordance with a predetermined error pattern which is repeated at a lower repition frequency than the code. The channel receiver is so designed that its output can only be held in the selected state when both the signature code and the error pattern in the received signal are correct. If a fault is detected, the receiver output is shifted to the most safe state of the function.

Abstract: New reactants for catastrophically embrittling steel having a hardness of ckwell C40 or greater comprising an amalgam of 98 to 99 weight percent mercury, the balance being lithium and indium; and an aqueous solution of vanadium pentoxide, and methods for applying said reactants to the steel.