VR sensor polarity detection

I’m working with a traditional VR (variable reluctance) sensor that is used to measure RPM and serve as an angular reference point of an engine. It produces one pulse once per revolution on an engine that is running at say 240 RPM (or 4 pulses per second). The amplitude of the sensor ranges from about 5 volts (peak to peak) to about 15 volts (peak to peak).

I’m trying to think of a relatively simple/elegant way of determining if the signal coming off the VR sensor is starting on the upslope and going positive first, then going negative, or vice versa. See drawing to get the idea.

Is the data sheet on the sensor of any help?


Paul_KD7HB: Is the data sheet on the sensor of any help?


It's a proprietary Bosch sensor, so not sure there is a datasheet, but the challenge is really a more basic "how does one approach this" kind of issue. The signal from the sensor is like my drawing, as viewed on the scope, and I'm just trying to come up with a non-clumy approach to figure out if it's starting up the upslope or downslope.

If it is a 2 wire sensor ( no idea as no details given except "Bosch") perhaps just swap the 2 wires over if you want positive going pulse first and it's the wrong way around.

Worked for me on a system I worked on.