Air gap for VR sensor

[serpentnoir]

I am trying to find out what air gap is needed for the signal from a VR sensor to disappear. I know this may seem like a strange question but I know they are typically installed with 0.03~0.04" gap. Would a 1/4" gap be enough?

[john.p.clegg]

I'd try and get it a lot closer than that if I was you... aim for the 0.035"

John

[serpentnoir]

My question is the reverse of your answer. I am looking at the minimum air gap necessary for the signal to disappear. I know that as I pull the sensor away from the wheel, the signal will get fainter.

[66fb]

I agree, on the face of it, it is a strange question. I think the amplitude of the VR signal also varies with the speed of the tooth passing under it. So, first you'd need to spin at your upper rpm limit and move the sensor away until it "disappears". This point will be as dependent on your install (trigger wheel material, thickness/shape of tooth, sensor/wheel axis alignment, sensor quality and the instrument you are using to detect the VR output) as your location will be to time of sunrise.

Hope this helps

[serpentnoir]

The reason for the question is actually quite simple. I am using a Ford VR sensor to detect cam position on a GM V8. GM put holes in the cam gear to reduce weight and inertia. I don't want the edges of the holes to affect the signal. One trigger tooth will be welded on the gear and I'm trying to figure out how tall to make the trigger in order to keep the sensor away from the "holes".

[66fb]

I can see where that could be a problem. An alternate solution (if needed) might be to add a bit of signal conditioning -depending on what characteristics your trigger signal needs to have. What does the circuit you are feeding this signal to need for an input?

Just curious, are you doing this sensor/pickup in the front cover of the engine?

[serpentnoir]

The circuit is Ford EEC-V.

And yes the sensor is going in the existing hole on the front timing cover of a GM LS2 V8. GM has a Hall effect sensor in that hole.