Turbo speed sensor going to use optics instead ?

[Seth]

I have no idea, but I wonder what the response time is for your
detector? Can is cycle on/ off at ~1/20 millisecond (assuming 10 blades
at 120,000 rpm). Not trying to shoot holes in your plan, but it might be
worth looking into. I have usually seen the tip of one blade painted
white for an optical tach in compressor wheels.  That might mean a
rebalance with the paint? I don't know.

-Seth

"Mike (Perth, Western Australia)" wrote:
> 
> At 10:24 AM 9/03/2000 +0100, "Espen Hilde" <mwichstr at online.no> wrote:
> >Take the compleate turbocharger and fix the wheel so it stands still.
> >Drill trou the cower so you hit near the outer edge of the compressor
> >wheel, turn the wheel 180 deg. drill trou the wheel once more to have the
> >balance fixed.Or offset the hole closer to senter if you dont want 2 pulses
> >
> >for each rpm.Glu the optical sensor in the back hole and your laser on
> >front cower.Maybe you have to clean the sensor once in a while....
> 
> OK - have given this some thought (and a short visit to my w/shop),
> decided its not a good idea to mess around with the comp wheel which in
> any way upsets balance or structural integrity - will also save me
> doh in the event the balance does get upset.
> 
> So,
> This is what I've decided to do for the fist attempt:-
> 
> a.      Cheap laser pointer
>         positioned to glance off or reflect off the blades
>         This could be axially mounted or better would be where the
>         beam is interrupted by the blades directly.
>         (Changing the batteries could be a pain ;-)
> b.      Sensor mounted in comp cover but, behind a tube (1/4")
>         so the surface is away from any dust/oil,
>         ie. tube at r/angles to stream, sensor mounted at end of
>         tube about 1" away from edge of comp cover.
> c.      CPU to trigger counter or time between pulses, depends
>         on number of reflections/edges detected. CPU can use
>         time between pulses at low speed or count in gate time for
>         high speed - with upper lower limits. Such as alarm if
>         wheel stops and alarm/solenoid if wheel above preset rpm.
> d.      Calibrate with infra-red optical tacho instrument
>         and adjust laser/sensor position to suit multiple of
>         sensed speed (given number of edges etc).
> 
> The other way which came to mind was passing an AC field through the
> comp wheel and using a variable reluctance pickup - that way I wouldn't
> need to drill the comp wheel - I think the optical one looks best...
> 
> I'm interested in any other suggestions,
> 
> tah,
> 
> :) mike
> Perth, Western Australia
> 
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