Abstract: A detector for detecting a characteristic and a speed of a vehicle includes a first magnetic field sensor for generating a first analog signal indicative of changes in magnetic field strength adjacent the first sensor in response to the vehicle passing. A differentiating circuit differentiates the first analog signal and produces a first output that changes binary state in response to detecting a predetermined change in the differentiated first analog signal. A counter accumulates values at a predetermined rate and a microprocessor stores values of the counter corresponding to each change in the binary state of the first output of the differentiating circuit. The microprocessor converts the stored counter values into a first time series profile corresponding to changes in the first output of the differentiating circuit and accumulates and stores a count of a characteristic of the passing vehicle based on the first time series profile.

Abstract: A sensor for detecting a magnetically permeable mass by the disturbance of the earth's magnetic field in the vicinity of the sensor comprises a ferromagnetic strip with a conductive winding wrapped thereabout, a means for magnetically biasing the strip such that regardless of orientation the earth's magnetic field and the strip placing the ferromagnetic strip in a position on its BH curve where the slope is substantially linear, a means for generating an analog signal indicative of the inductance of the winding as the earth's magnetic field is disturbed in the vicinity of the ferromagnetic strip causing a change in the inductance of the winding, a means for digitizing the analog signal at spaced time intervals to produce a series of digitized values, and a digital computer means for processing the digitized signal values to characterize the presence and/or motion of the permeable mass.