AFM measurement/backpressure (was Turbo speed sensor)

[Mike (Perth, Western Australia)]

At 05:28 AM 8/03/2000 PST, you wrote:
>"Mike (Perth, Western Australia)" <erazmus at wantree.com.au> said:
>
>>I really would like to do a turbo speed sensor - so far no reply from
>>the emails I've sent out to distributors - not even a "we don't do it" :(
>
>Turbocharger RPM is also sensed via a variable-reluctance pickup at the 
>compressor-wheel nut;  that is the inlet side, so it won't be quite as hot 
>as the outlet side (we hope).

mmmmm OK, given the compressor speed I was of the opinion the VR type
pickup would just plain saturate at high turbine speeds - whereas the
optical one would give me more bandwidth.

Also I would guess it would be problematic to mount a sensor close
enough to the comp nut given its position, air flow restriction (perhaps
minor) and care to avoid it falling into the comp on high flows etc

As I haven't done anything on this so far I might have another look at
the magnetic pickup then, do you have any ideas of component p/n's or
do you consider the off the shelf VR pickups might be OK from a hobby
outlet like Tandy's etc ?

Tah for that - defintiely worth of another look - thanks :)

I suppose when I next take the turbo out - I could install a small piece
of ferrite into the rim of the comp wheel (rebalance it after of course),
or would this be too risky given the rpm and centripetal forces ?

Has anybody actually used an optical tacho to see what sort of rpm's
the comp wheel does at idle ? And yes I know that getting access is a prob
due to AFM being removed - I'm just asking since I did that on my system
in 'limp' mode (AFM off) yet could idle car and run it (very rich) up
to 2000rpm... At least it let me see if the turbo was OK spinning at idle
after it was re-assembled...

I've been told its around 300rpm - though I didn't have a optical tacho
handy - it looked about the speed of a regular floppy drive though ~`:o




Rgds ~`:o)

Mike Massen         Trading as "Network Power Systems" and "Network Computers"
Perth, Western Australia  Ph +61 8 9444 8961  Fx +618 9264 8229 (fax -> email)
Products/Personal/Client web area at http://www.wantree.com.au/~erazmus
 (Current pics - trip to Malaysia to install equipment in jungle power site)

Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.

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