Turbo speed sensor going to use optics instead ?

[Mike (Perth, Western Australia)]

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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