AFM measurement/backpressure (was Turbo speed sensor)

[mike mager]

The quotations are getting complicated here (or I just need some sleep?).

>From: "Mike (Perth, Western Australia)" <erazmus at wantree.com.au>
>Reply-To: diy_efi at diy-efi.org
>To: diy_efi at diy-efi.org
>Subject: Re: AFM measurement/backpressure (was Turbo speed sensor)
>Date: Wed, 08 Mar 2000 22:17:05
>
>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.

Excellent point!;  I have read of it, but I don't know what type of VR 
sensor they had.

>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 ?

Wow!  A shot-peener spins more slowly than a compressor!  A radial mounting 
would do, but that would be a permanently drilled hole.

I mainly just wondered why nobody had mentioned that, with certain (I don't 
remember which) books mentioning it;  the application may have been 
laboratory only.  Definitely sounds interesting, at the least.  Aircraft 
engines have turbine tachometers, BTW.

Mike

>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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