Minnesota Mining and Manufacturing Company

Martin C Henderson

Earl B Hoekman

Ralph James Koerner

William D Jordan, Jr

The period T.sub.nv of an oscillator signal is measured. A number N.sub.meas of cycles of the oscillator signal is determined based upon the measured oscillator period T.sub.nv and upon a desired minimum change in inductance .DELTA.L (sensitivity) which will result in an object being detected. The N.sub.meas cycles of the oscillator signal represent a measurement period. The length of the measurement period, defined by N.sub.meas oscillator cycles, is periodically determined. The length of the measurement period is compared to a reference value. An output, based upon the results of the comparison, is provided. Thereafter, the desired minimum change in inductance .DELTA.L (sensitivity) may be automatically adjusted by determining an average magnitude change in inductance .DELTA.L.sub.ave caused by a plurality of vehicles. The number N.sub.meas of oscillator cycles, which define the measurement period, is recalculated based upon the average magnitude change in inductance.

Vehicle detector with automatic sensitivity adjustment

A strip material (18) for forming an inductive loop (10) adapted to be applied to the surface of a roadway (12). The strip material (18) consists of and the loop (10) is formed from a ductile, flexible, flattened, extensible conductor (20) and a protective covering (22). A protective underlayment (24) is optional. The conductor (20) may be formed from a compressed, flattened metallic wire braid (28) or from a wire mesh containing 25% to 75% voids. The protective covering (22) may be formed from either combination unvulcanized elastomer precursor base sheet (30) and a vinyl based polymer support film (32), or a covering (26) selected from the group of epoxy, polyester, urethane and polyurethane.

Growing community of inventors

Los Angeles, CA, United States of America

Martin C Henderson