http://worldcat.org/entity/work/id/496278329

Vehicle detection - phase II. MGVD development. Final report

The FHWA vehicle detector concept called the Magnetic Gradient Vehicle Detector (MGVD) was examined by this project. The MGVD consists of an electro-magnetic transducer in the pavement, interconnecting wiring, and transmitter/receiver electronics in the traffic control enclosure. The transmitter electronics energizes a transmitter coil at one end of the transducer. The resulting field is loosely coupled into a null coil near the transmitter coil and at a receiver coil situated at the opposite end of the transducer. The null coil and receiver coil are wired in phase opposition such that their output is nulled. A vehicle passing over the transducer varies the electromagnetic field resulting in both an amplitude and phase variation to the receiver coil output which is detected by the receiver electronics. Since the MGVD transducer is approximately 1/2 inch wide, 2 inches deep, and 84 inches long, it is simpler to install than the inductive loop and could be a cost-effective alternative to the inductive loop detector.

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