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Electric loop stop light sensors - do they work for you?(14 posts)

Electric loop stop light sensors - do they work for you?PdxMark
Jan 22, 2003 12:35 PM
The things that come to mind waiting at a stop in the rain...

Most well-adjusted electric loop stop light sensors seem to be able to detect me whether I'm on my Al Canondale or Ti Litespeed. The trick is to be positioned just inside the loop rather than being in the center far from the actual loop.

I assume it's because they can detect the small bits of steel low down on the bike, which I assume would be the Chorus or Centaur BB spindles and maybe even the pedal cleats. Is there a road group that has no steel - like Record? Do the electric loop stop light sensors work for bikes with no steel in the frame or group? If so, how?
I don't know how, but they do,TJeanloz
Jan 22, 2003 12:39 PM
My bike has very, very little steel on it, and the electric loop sensors work fine. I have no idea how they do it.
I've had trouble with them ...Humma Hah
Jan 22, 2003 12:47 PM
My cruiser ought to trip 'em as well or better than most bikes here. No lack of iron, including the rims. But my original attempts to trip a loop by riding on the wire at the right edge (closest to my path) never seemed to work.

I encounter a couple of them on my commute home that seem to respond better if I ride straight down the middle.
Inductance loopsAlexx
Jan 22, 2003 12:56 PM
They work on the principle of induction, where the magnetic field from any ferrous material passing through the loop creates a small current, triggering the light. Chances are, any bike will have some ferrous material (SS nipples, pedal spindle, chain, bearings, tire beads, innertube valves, or even cleat screws), so as long as the sensor is set sensitive enough, it should work.
That's not how they work.the other Tim
Jan 22, 2003 2:32 PM
The loops are inductors - capable of storing energy in a magnetic field. Inductance changes when a ferromagnetic, paramagnetic or diamagnetic material is present in the magnetic field. Inductance is almost always measured by measuring AC impedance in an RL or RCL circuit.

Current is not induced by the material; the inductance is changed.

Your best chances of triggering the single loop sensors is at the edge of the loop. For the figure-8 type, you want to be right at the center of the 8 (right here ->8).
re: Electric loop stop light sensors - do they work for you?moo2
Jan 22, 2003 1:00 PM
If you're having trouble tripping the lights, try stopping in the middle of the loop. Then unclip one foot, and lean your bike over in the direction of the unclipped foot. This way, the metal in your bike presents a much larger area for the inductance loop to detect. Trust me, it works.
I've heard & read that being just inside the loop is best...PdxMark
Jan 22, 2003 3:38 PM
you're closer to the coils that are trying to sense you.

"Standard loops are rectangular or square in shape. They are somewhat sensitive over the area in the center, most sensitive over the outer wires, and least sensitive outside of the loop. As a result, a bicyclist stopping at the curb would probably be outside the loop and would go undetected. No green light."

Here's one link:
I have Al bikes with Record and the loops work for me - here's howlonefrontranger
Jan 22, 2003 2:06 PM
The ones here in CO seem to be fairly sensitive, 'cos I could never trigger the ones in Cincy with any bike I owned, regardless of how I tipped them or whether it was the steel fixie or my lugged carbon Giant Cadex.

My Easton Al Morgul Bismark with Record triggers the Boulder sensors just ducky. My Columbus Airplane Al Colnagos trip them okay as well (one Centaur, one Record), as will the steel fixie with the NR/SR pista grouppo. Haven't tried it yet with the Mongoose (BMX bike) but if anyone's interested I bet that pig of a steel 3-piece crank will do the trick :)

The secret, as someone else mentioned, is not only for your jurisdiction to set the sensors fine enough, but you also should tip the bike so that the drivetrain (your chain is steel regardless of group) presents a larger "profile" to the loop.

I personally find that tipping the bike right over top of the wire is what does it for me.
Ahhhhh... the CHAIN!!!PdxMark
Jan 22, 2003 2:52 PM
That's what I forgot!!! Even with a total carbon, Ti, etc., there's always a chain.... Now I can sleep tonight... Thank you!
We're suppost to stop at street lights ? :) nmMatt Britter
Jan 22, 2003 2:53 PM
I have so much lead in my @ss that it's no problem nmContinental
Jan 22, 2003 2:54 PM
re: Electric loop stop light sensors - do they work for you?Red Novara
Jan 22, 2003 3:40 PM
excerpted from a bicycle FAQ --(

Can't attest to the physics lesson, but following the suggested rule works for me.

i A traffic loop detects metal objects such as cars and
i bicycles based on the change in inductance that they
i induce in the loop. The loop is an inductor in an LC
i circuit that is tuned to resonate at a certain frequency.
i A metal plate over the loop (like a car) causes the
i magnetic flux to be shorted, reducing the inductance of
i the loop. This causes a change in resonant frequency,
i which is detected and sent to the signal controller. One
i of the ways of testing a loop is to create a loop about 2
i feet in diameter with several turns of wire (connecting
i the ends) and placing the test wire in the middle of the
i traffic loop. The test wire should cause a detection, if
i all is working.

i The same effect is seen with a vertical piece of metal,
i such as a bicycle, but is weaker. Because aluminum
i conducts electricity quite well, aluminum rims help.
i Steel rims are OK. Non-metal rims cannot be picked up at
i all. A bicycle with aluminum rims will cause about 1/100
i the change in inductance of a car.

b Bicyclists should, as a general rule, place their wheels
b over one of the slots to maximize their chance of being
b detected.
i That is where the magnetic field perpendicular to the
i wheels is strongest. Bouncing the bike or moving it back
i and forth does no good. If you have a metal frame,
i another tactic that may work is to lay the bicycle down
i horizontally inside the loop until the light turns green.

i Bob Shanteau, PhD. PE
i Registered Traffic Engineer
re: Electric loop stop light sensors - do they work for you?siclmn
Jan 22, 2003 4:21 PM
Most of the loops in the city of Seattle are marked with an X which is always on the front left or the front right of the loop. You ride your wheel onto the X and wait. Sometimes they work and sometimes they don't.
re: Electric loop stop light sensors - do they work for you?Spunout
Jan 23, 2003 5:35 AM
Ottawa: The loop closest to the curb has yellow dots placed on it, just park your bike on one and the light will go. In fact, there are commuter routes/bike lanes that have their own signal loop to chang the light. THat is sweet.