||09-28-07 12:05 PM
Originally Posted by jur
. . .These detector loops don't work by detecting magetic material, they work by changing inductance. This is achieved by any conductive material being inside the high frequency magnetic field generated by the loops. The field induces circulating (eddy) currents in the car and this is detected . . .
Are you sure? I have a comment and a question. The comment: I have noticed that when I am driving, cars with steel wheels will trip the sensor more reliably than cars with alloy wheels, and that when driving on alloys I have better luck approaching the limit line with the steel oil pan lining up over the "sweet spot" rather than the wheels. Once I was on a moped and couldn't get the light to change at all. I happened to see a steel hub cap at the curb, retrieved it, and waved it over the sensor with immediate results. This leads me to believe that it's not only the conductivity of a metal that makes the difference, but also whether or not the metal is ferrous.
And now the question: if I'm right about ferrous metals making a difference, and you are right about the sensor being triggered by a disruption of its magnetic field by a vehicle, would it not follow that a scooter, made mostly of alloy, might have trouble tripping the sensor? If a hubcap strapped to the bottom of the scooter would increase the scooter's "magnetic foot print" (that's layman
, not lame man
) couldn't it be possible that an exceptionally strong magnet attached to the underside of the scooter could provide a similar "footprint" to the larger but non-magnetized hubcap?