GB788453A - Improvements relating to the detection of railway vehicle wheels passing a fixed location - Google Patents

Abstract

788,453. Railway signals. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Feb. 21, 1956 [March 9, 1955], No. 6955/55. Class 105. The passage of a vehicle wheel past a fixed location as in the counting of the number of axles into and out of a railway track section to give an indication when a train has left a section, is detected by a single magnetic structure 4 disposed at one side only of the track rail and having an open magnetic circuit constituting part of an inductive device L having an exciting coil 3 connected in series with an impedance element for energization from an A.C. supply, e.g. 50 p.p.s., the said device L being disposed close to a running rail 1 so that a passing wheel 2 will cut a leakage flux path of the magnetic circuit to produce a temporary change in the effective impedance of the exciting coil, this change being detected for example by the unbalance of a normally balanced impedance bridge in which the series combination is incorporated. As shown, the bridge impedance in series with the exciting coil 3 is preferably a capacitor C and the other two series arms also consist of an inductance L<SP>1</SP> situated out of the influence of the passing wheels and a capacitor C<SP>1</SP>. The capacitor C is such that in the normal conditions, in the absence of a wheel, the inductance of the exciting coil 3 of the capacitor C just does not resonate at the supply frequency but passes through resonance as a wheel passes by. The magnitude of the change, amplified if necessary, actuates a counting device CR of known form. Two such counting devices are operated respectively at the entrance and exit ends of the section of track and the counted outputs compared to indicate whether or not the section has been vacated. To determine the direction of movement of the train, two similar detecting arrangements will be provided with their respective devices L placed along the track a suitable distance apart either on the same or opposite sides of the track and a device provided to indicate which bridge becomes unbalanced first.