Railway wagon wheel passage detection circuit - employs open gap detector coil in oscillatory circuit excited by oscillator emitting constant energy pulses

摘要

The appts. provides wide dynamic response with insensitivity to external perturbations. A sensor (1) comprises an oscillatory circuit containing an inductor (5) wound on a magnetic core (6) with a capacitor (4) and connected to a receiving circuit (8) comprising a four terminal capacitor (16). This provides phase information for a comparator (19) acting as a pulse generator whose output is transmitted to the sensor via a transformer (9) to provide a closed loop circuit. Amplitude information (11) is provided for a second sub-assembly which controls an amplifier and relay circuit which operates when the wagon wheel is not present. The oscillator circuit comprises a low leakage capacitor and a coil of 'Litz' wire around a U-shaped ferrite core, of which the branches are directed towards the election zone.