On Thu, 18 Nov 2004, Jinx wrote:

>>> Wondered about that last time it happened - surprised that
>>> 2000+ people seem content. I know I am for the time being
>>>
>> Content, huh?  So did you exorcise the demon that was infesting
>> your computer?  If so, how and so on... enquiring minds want to
>> know
>
> Enquiring minds will have to wait. I gave that PC the two-finger
> salute and a grunt for now - too busy (and how) with asm
>
> Here's a PIC-ish question though.........
>
> 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.
> 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 ?

Paste a large round colored dot on a blade (or two opposite) and film the 
device in operation using a strobe running at 25Hz (2 turns = 1 pulse). If 
you use an adjustable aperture on the cctv camera stopper it down until 
you see noise in the dark parts of the image. This makes the electronic 
shutter open up wide and reduces flicker. The angle is deduced by 
measuring the h/v size of the dot after calibrating with still turbine. 
The camera can be mounted off axis in case on axis is not good (how many 
hp for that turbine ?).

Things that mount in fast rotating machinery are hard to make and hard to 
keep calibrated.

Peter
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