| 摘要 |
<p>The detector is used in railway applications to detect the passage of a train, or to check the number of wheels passing, and hence the length of the train. The extra eddy current losses and the changed self inductance of coil attached to the railway line allow detection of the passage of a metal wheel. To enhance the reliability of the detection, the trackside inductor (L1) is incorporated in a resonant circuit (L1,C1,TR2,C3) which is excited at a sub-multiple of the normal resonant frequency. The reduction in current as the circuit falls out of resonance due to a passing wheel is transformer (TR1) coupled back to the emitter of the switch mode transistor (T2,T1) sub-resonant frequency generator, causing a fall between 50 and 75% in the output signals (14), offering reliable detection by a comparator.</p> |
