Testing with a digital meter in this type of circuit is inherently problematic if you are trying to see voltage spikes as you turn the wheel.

You really need an analog (needle) meter to see this type of transient, and that would probably only work if the meter was very sensitive as you'd be measuring voltage not resistance.

I wouldn't expect to see ANY change in resistance as you turn the rotor, because that's not how the circuit works. You might see the readings change because voltage was induced into the circuit, but that's a false reading not reflecting resistance. It would indicate that it was working, however.

It's an inductive sensor so no change in resistance would occur. Now, impedance WOULD change as you spun the rotor, but not DC resistance. Remember, (or learn for the first time) that impedance is a function of frequency while resistance refers to DC. So if one were to put a test frequency through the sensor with a current meter in series, then you may very well see spikes as the rotor turns. Actually, I don't know squat about this particular circuit, but it's doing one of two things: Either measuring inductively generated pulses, or detecting spikes in a provided AC signal through changing impedance. Either way, the only thing an ohm meter will tell you is if the coil has continuity. I would suspect that it uses the latter approach, since you would have no variance in the size of the spike with respect to wheel speed. Inductively generated pulses would get bigger in voltage and smaller in duration as wheel speed increased. But, either method would work......

If you were to hook up an oscilloscope set on high sensitivity, you should certainly see spikes as you spin the rotor. If not, supply the sensor with a 1K test tone, and meter the current swings across the circuit as you spin the rotor.


As far as fixing on of these, they are nothing more than a coil of wire wrapped around either a ferric core or a magnet. I would suspect it's a ferric core and not a magnet, but I've never opened one before. I can't see the need for a magnet. If you can get it apart and repair the broken wire, and get it back in one piece, it should be fine.

-edit-

Actually, I could see the need for a magnet, if it were using inductively generated pulses rather than AC impedance swings. Somthing would have to be magnetized for that approach to work, either the sensor or the little ABS studs on the rotor....

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-tp