automatic gates and motorcycles
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Joined: Jul 2010
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From: Central Texas
There are two types of sensing systems used for traffic lights.
One is the loop type system which uses a loop of wire and operates at a tuned frequency, same thing as the metal detectors used for looking for gold and other stuff on beaches, just has a larger loop. When a large enough mass of metal is near, the loop will shift the frequency to signal presence. at some traffic lights you can see the rectangular cutout for the loop. Best positioning, IME, is being right on top of the wire with front wheel over the corner of the loop.
The other type of sensing system is "loopless" and uses a 3-axis sensor to detect small changes in the earth's magnetic field. an object with enough metal will cause slight distortions in the magnetic field and will allow the sensor to detect. Usually these sesnors are located in the middle of the lane and can't be located easily.
I designed loop type presence detectors for a company that makes rail yard equipment. Did a lot of testing as well. Don't know how a magnet could trip a loop type sensor since it's based on frequency. However, it's conceivable a strong magnet could trip the loopless type.
One is the loop type system which uses a loop of wire and operates at a tuned frequency, same thing as the metal detectors used for looking for gold and other stuff on beaches, just has a larger loop. When a large enough mass of metal is near, the loop will shift the frequency to signal presence. at some traffic lights you can see the rectangular cutout for the loop. Best positioning, IME, is being right on top of the wire with front wheel over the corner of the loop.
The other type of sensing system is "loopless" and uses a 3-axis sensor to detect small changes in the earth's magnetic field. an object with enough metal will cause slight distortions in the magnetic field and will allow the sensor to detect. Usually these sesnors are located in the middle of the lane and can't be located easily.
I designed loop type presence detectors for a company that makes rail yard equipment. Did a lot of testing as well. Don't know how a magnet could trip a loop type sensor since it's based on frequency. However, it's conceivable a strong magnet could trip the loopless type.
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