Vehicle speed measurement system using inductive pick=up coil - uses vehicle to vary damping of tuned circuit which varies VCO output

摘要

A vehicle speed measuring device includes a pickup coil which is placed in the vehicle track. Together with a capacitor (11), the pickup coil (10) constitutes a resonant circuit coupled to a VCO (12). The voltage induced in the resonant circuit is also fed to an output contact (14) by way of a demodulator (13). The output of the VCO is connected to the output contact through a low pass filter (15) having a time constant greater than the period of time that the vehicle spends in the vicinity of the pickup coil. The presence of the vehicle varies the damping of the resonant circuit and hence the output of the VCO.