Lpc2000

--- In lpc2000@yahoogroups.com, Onestone <onestone@...> wrote:
>
> I thought the commercial systems used phase shift to determine distance?
> 
> Al

I believe the phase shift approach is used to measure distance moved,
not absolute position.  Laser interferometry (counting interference
fringes or counting wave nulls) has been around for many years.  We
used it to calibrate the optical encoders on numerical control
equipment way back in the late '60s.

Richard