Originally Posted by bostontrevor
If you care to explain, referencing the appropriate physics, how an inductive loop detector works and why it will not respond to a non-ferrous metal, I'm all ears (eyes).
Otherwise we have it on the authority of a EE that they work just fine with aluminum, there's nothing special about steel or magnets other than the fact that they conduct electricity. I've provided real-world hands-on examples of how non-ferrous metals can interact with a magnetic field (and all detection of any kind is premised on interaction--if you can interact, you can detect). Or perhaps we shouldn't make reference to wheels, levers, or any of the other simple machines that seem to frequently play a roll in the world of cycling because that's science, not bikin'!
So what's the deal? How is it that aluminum doesn't doesn't trigger the detector apart from the fact that the detector is simply maladjusted. Sometimes my very ferrous rides don't trigger them either.
It depends on where you are relative to the most sensitive part of the loop and to how sensitive the loop has been set by traffic engineers. Some loops have been desensitized because of heavy (volume) or heavy (size) cross traffic. Try to ride straight down the middle of quadrapole type sensors (the figure 8 kind). For dipole type, ride straight down the wire on either side (these are much harder to trip). This assumes that you can see the wire cuts in the pavement. If you can't see them, it's a bit like playing Battleship
You just hope you hit it right.
Or you may be running across the more frequently used, but still uncommon, motion detection sensor. If the traffic lights have what looks like little telescopes on each pole, it's probably a motion detector. I only have a couple of these on my routes but they can be a bugger to get tripped. I finded that if I do a little left (or right) hook just as I get to the light, I become a bigger target and the light will trip.