Vehicle detection systems

摘要

In the disclosed system the speed of a vehicle passing over the sensing coils of the detection system is determined by sampling the envelope voltages occurring during the leading edge portion of the disturbance in the envelope of the received signal produced by an approaching vehicle. This is accomplished by sampling the envelope voltage at a first instant at which the slope of the leading edge is at a maximum and at a second instant occurring at a fixed time interval subsequent to the first instant. The voltage sampled at the first instant is then subtracted from the voltage sampled at the second instant and the difference divided by a voltage sampled at a third instant at which the slope of the leading edge first starts to decrease to produce a signal indicative of the vehicle speed.