Forwarded: Re: Airflow measurement - again...

[kleenair at ix.netcom.com]

Hi Andrew,

Thanks for the explanation.  This is my first exposure to LDA, so I have 
no idea how sensitive the system is.

1)  How would the system determine the direction of travel of the 
particles?  More importantly, how does it detect direction changes in 
dynamic flow, or what kind of errors are caused by turbulance and eddies 
in the air flow, etc.?

2)  Do you think this is applicable to inside the manifold, or on the air 
inlet ducting somewhere.  It seems the laser lenses might be hard to keep 
clean.

Thanks for the input.

Best Regards,
Mazda

RABBITT_Andrew at mv8.orbeng.com.au wrote:
> 
> LDA requires particles in the air-stream to work.  Fortunately the
> dust present is enough.  The system works by intersecting two laser
> beams at the point you want to measure the velocity.  At the
> intersection, the two beams form interference bands.  As particles
> travel through the intersection, they reflect pulses of light at each
> constructive interference fringe.  A photo-detector senses this
> reflected light.  The frequency of the detected pulses is directly
> related to the speed of the particle, which is related to the flow
> velocity.  Note though that this is not a MASS flow detector
> 
> Andrew Rabbitt