Quote:
Originally Posted by Rifleman
If my understanding is correct...
Induction loops consist of one loop or coil through which current is passed and a static magnetic field is generated. A second loop, or coil sits with in that static field. The detection loop.
If the first loops magnetic field remains steady and constant, no current is generated in the second detection loop. However if a iron or other magnetically inductive material is passed through the field, this causes the field to fluctuate. A change in the magnetic field will induce a current in the detection loop and will register a signal...
so the two things that are needed are a large piece of ferromagnetic material, and relative motion between it, and the induction loops.
a relatively small change in the magnetic field produces a significantly large signal if the number of turns on the detection coil are high enough...
so, by passing an actual magnet through the area where the detection coil is located, a significant signal can be generated.
As most modern design motorcycles are moving away from ferromagnetic material toward Aluminum, Magnesium and other exotic materials (carbon fiber), the detection loop has less material to upset the magnetic field.
Perhaps I'm wrong, but this sure seemed to fix the problem for all but the most "blind" traffic sensors.
Perhaps i'll line my belly pan with a bit of steel sheet metal... Two stones, one bird as it were.
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It's not the disturbance per se of the magnetic field directly that the sensors pick up but the disturbance created by eddy currents which change the field and the sensors monitor. The eddy currents don't get extra powerful if done from purely a magnetic field, otherwise a copper wire based electromagnet would be the best solution. The eddy currents play across the surface of the metal and it's these eddy currents which create a disturbance in the field that the sensors measure. Your magnet works since it's still in practice a flat piece of iron that's real close to the ground. A really thin piece of sheet steel should work wonders and with how low a bike sits, should actually do a better job than the axle of a car due to sheer flat surface area. Also, aluminum foil theoretically should be able to produce a similar, if not reduced effect. So I want to someday try lining the belly pan of my bike with aluminum foil and see if the magnetic field on induction loops are designed similarly as some metal detectors are. Ask a metal detecting enthusiast how many aluminum cans they've dug up because their detector called it a coin.
I used to have the national Department of Transportation's Traffic engineering and design handbook in digital format and it goes in length on theory of operation and design. A very interesting read for the few of us that like that sorta thing.