> I need to measure the variable angle (19-32deg) of a turbine
> blade in real time. Turbine is spinning at ~ 3000rpm. There's a
> mechanism optically measurable by the PIC, but the only room
> that seems available for the PIC is on the end of the turbine shaft.
> Which is doing ~ 3000 rpm. According to
> 
> http://microvet.arizona.edu/Courses/MIC328/Waynes%20World/AppendixE_centrif.
> html
> 
> I could expect ~ 100g at 1cm from the axis of rotation. Ooo-er.

I found that value hard to believe, but running through their example
and applying the corrections for scaling, I also get 100.8 G.
I had NO idea it would be so high. (1000=>3000 RPM factor 9,
10cm =>1cm factor 0.10  G=ohmega^2*r

> If I used a 10F (or 12F DIP) at the centre of rotation this would
> get the g-forces down considerably (maybe 20g ?). For the PIC
> at least. There's still the problem of an LED/receiver surviving >>>
> 100g. Luckily this doesn't have to be for extended periods, only
> long enough to characterise thrust per angle under various conditions,
> but I worry about the cumulative effect on bond wires etc
> 
> Any other suggestions ?

Measure and calibrate whatever shaft, control arm, lever is
used to change the angle. Instead of mearsuring angle directly,
measure the control input.

Use magetics instead of optics to measure the shift?
Have it change the frequency of an oscillator (LC) that you
mount shaft center, and pick up the emission from a non
rotating location?

Can the measurement be made from a stationary point?
e.g. distance measuring Optocoupler? You'd get a 50Hz
waveform but presumably you could trigger from some
sort of shaft index.

What about imaging using strobe lighting?

How about using a laser diode to illuminate a mirror surface on the
control arm/lever/whaterver, and look at the timing change
in the control reflection relative to shaft position?

I'm bascially saying find a way to NOT have to mount the PIC
(or anything else) on the shaft.

Presumably if you are doing a profile, you have some way
of controlling angle while the turbine is running, so measure
that input.


Robert

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