Magnetic sensor and circuit for detecting the edge of a target as it passes the centerline of the sensor

In a magnetic sensor for detecting a ferrous target separated from the sensor by a gap, the sensor having a centerline and means for providing an analog signal representing the rate of change of magnetic flux in the gap as the target passes the sensor moving generally at right angles to said sensor centerline, the target having an edge extending transverse to the direction of relative movement and in the direction of the sensor centerline, means for detecting alignment of an edge of the target with the centerline of the sensor comprising:

• means for differentiating said analog rate of change signal, the analog differentiated signal having a zero crossover point corresponding to the time at which said edge of the target passes the centerline of the sensor;
• and
• means for detecting the zero crossover point of said analog differentiated signal to provide an output signal which corresponds to the time at which the target edge is conincident with the centerline of the sensor.