[Al Skierkiewicz]

Mike,
I have been thinking about this since I saw your post yesterday. If I am reading this right, you need to know the projection of each blade as it passes a fixed point correct? BTW, I think your first estimate of sample rate was accurate. i.e. 20 turbine blades mounted on a shaft spinning at 15,000 RPM passing a sensor seems like it's in the right neighborhood for 336kHz. At that sample rate, it seems that ultrasonics would not work, Hall effect or other metallic sensors would likely not work either. That leaves optical or some form of radar I think. It seems I read somewhere about an optical interferometer being used in just such an application.