SPEED DETECTION METHOD AND APPARATUS

A method and apparatus, operable over a given speed range, for detecting the speed of an object moving past a sensor which develops two electrical signals, each enduring for a time interval that varies inversely with the speed of the object and in inverse relation to the distance between the object and the sensor, the signals being spaced by a time gap that varies inversely with the speed of the object and that also varies as a function of the distance between the object and the sensor. A first capacitor circuit, charged prior to initiation of the sensor signals, is discharged at a given rate during one signal and discharged at a second faster rate thereafter until the other signal starts or until expiration of an extended time interval longer than the longest time gap for the speed range. A similar capacitor circuit is discharged at the given rate during the other signal and at the second rate thereafter until the one signal starts or until expiration of the aforementioned extended time interval. The charges on the two capacitor circuits are compared; the largest residual charge indicates the speed of the object and its direction of travel.