Patent GB-822381-A (GB)
Title: Improvements in or relating to railway track apparatus for interaction with a movingtrain
IPC: B61L13/04
Filed: 1957-03-13
Abstract: 822,381. Track apparatus for interaction with passing trains. WACHTEL, K. March 13, 1957, No. 8363/57. Class 105. Railway track apparatus for interaction with a moving train, for producing an electric current signal as the train passes and which may be used, e.g. in axle counters, includes a single or multi-stage oscillator comprising valves and/ or transistors and having in its positive feedback circuit coupled coils the coupling between which is influenced by the wheels of a passing train to effect a change in the amount of positive feedback so that when the oscillator oscillates in the absence of a wheel it ceases to oscillate in the presence of a wheel (closed circuit operation) and when the oscillator is quiescent in the absence of a wheel, it oscillates in the presence of a wheel (open circuit operation). The coupled coils influenced by a wheel may be negative feedback coils which are provided in series with the positive feedback coils in the respective oscillation and feedback circuits. By means of this series connection, disturbing influences may be compensated. As shown, the positive feedback coils L1, L2 are disposed at rail level and the associated negative feedback coils G1, G2 are disposed below the rails. Alternatively the negative feedback coils G1, G2 may be disposed at rail level and the positive feedback coils L1, L2 disposed below the rail. The temperature-sensitive parts such as the transistors are preferably contained in a sealed cylindrical container pushed into a tube A extending at least 0.5 m. into the ground. The same conductors F1, F2 are used for supplying power to the oscillator and for the transmission of the signals originating in the oscillator on the passage of a train and when a plurality of oscillators are used as in axle counting systems the oscillators are arranged to operate at respective frequencies, e.g. between 500 c/s. and 10 kilocycles/s. which are transmitted to the counting mechanism over the same lines F1, F2. In the example shown a single-stage transistor oscillator comprises across the collector electrode K and the emitter electrode E, a series circuit consisting of a resistance W, a condenser C and part of the positive feedback coil L1 between terminals a and b. The oscillation circuit includes part of the coil L1 between terminals a and c, condenser C1 and a negative feedback coil G1. The coil L is coupled to a second feedback coil L2 in series with a second negative feedback coil G2 coupled to the coil G1 connected across tappings a and c of coil L1 and the amount of positive and negative feedback is so adjusted that the generator oscillates when the rail is free, e.g. by adjusting the degree of coupling between the coils G1, G2, so that the counter E.M.F. induced in the coil G2 when the rail is free is smaller than the positive feedback voltage in the windings L2, so that the generator oscillates. The presence of a wheel reduces the coupling K between coils L1, L2 and the negative feedback predominates to such an extent as to stop the oscillator operating, resulting in the interruption of the transmission of the signal from terminals a and e of the coil L1 and the deenergization of relay M to indicate the passage of the wheel past the coils L1, L2. The coils L1, L2 may be disposed with their axes parallel to the rail or at an angle to the horizontal and may both be on the same side of the rail. Screening plates 1, 2 may be disposed below the coils L1, L2 thereby increasing the coupling between them and a passing wheel produces a greater variation in the coupling than without the plates 1, 2. A glow discharge tube GL connected between terminals a and d of coil L1 may be provided to protect the transistor T against over-voltages, e.g. in the lines F1, F2.