Speed and Ref Sensor data dump... :)

[Tom]

I posted some of this on that "other" board a while back, but wanted to start building up the tech info here. I did a ton of R&D on these sensors and how their signals look pre and post conditioning, and a few interesting tid-bits emerged....

I'll start with this video, showing my test set-up and how the gap and speed affect the pulse signal....

[Tom]

While testing, I kept noticing two recurring blips after the reference sensor pulse on the scope. When I'd spin the motor in the normal direction, the blips would come just after the reference pulse, but if I spun the flywheel backwards the same blips would appear just before the reference sensor pulse. They behave just like the primary pulse, just smaller. Among other things, that means the get bigger as the RPMS go up. I got up to over 2 volts peak to peak at about 800 rpm. I'm guessing at redline, they'd be a good multiple of that. After scratching my head a while, I finally realized the ref sensor was picking up the two pins on the flywheel that are there for the third diagnostic sensor (the one many people remove as useless). I can spin the flywheel by hand and watch the signal blip as those two pins pass below the sensor. The DME has no problem with them obviously, but I can't help but wonder if they are causing some of the trigger problems people experience with stand-alone systems? The modern VR sensor conditioning chips are "adaptive" and are pretty good at differentiating phantom pulses (especially the MAX9926 chip), but still. Those chips can detect pulse in the millivolt range, so seems possible they'd be fooled. I can't say for sure if it's causing anyone issues, but if I were experiencing triggering issues with the stock sensors on a stand-alone system, I'd sure remove those two pins and see it if helps....! They don't do anything, and removing them is free, so worth a try...

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I'm planning to take mine out and replace with a non-ferrous material of similar weight, on the assumption (?) that the flywheel is balanced with these installed. I'm wondering if this might also help with the starter kick-back issue many of us experience...