GB889798A - Improvements in or relating to magnetic detectors - Google Patents

Abstract

889,798. Track apparatus. N.S.F. Ltd. Dec. 23, 1958 [Dec. 23, 1957; Sept. 23, 1958], Nos. 39873/57 and 30330/58. Class 105. [Also in Group XXXVI] An electromagnetic detector for detecting the wheels of railway vehicles passing along a track comprises a source of magneto-motive force, a pair of polepieces associated with the source, and a coil wound about at least one polepiece, the polepieces being so arranged that passage of a wheel through an air gap between the detector and a rail induces a voltage into an output circuit. A U-shaped magnet, Fig. 1, having polepieces 1 each carrying a coil 3 is mounted horizontally with the ends of the polepieces facing the head of a rail 9. The coils are connected in aiding relationship between the base and emitter of the transistor 12, Fig. 3, the base-collector circuit of which contains a relay 15. As a wheel flange 10 passes through the gap, between the polepieces and the rail, the relay 15 operates and contact 17 closes to operate a wheel counter (not shown). Contact 16 closes to operate relay 18 which is given a slow release by capacitors 19, 20. The time constant of this circuit is made such that relay 18 operates only once per train and the changeover contact 21 of the relay may be used to effect any required control action or alarm. In an alternative form of detector (Fig. 2, not shown), the U-magnet is mounted vertically and has only one coil. Circuits are also described in which two detectors are used, either connected in series or in parallel to complete the energizing circuit of a further device.