Thanks everyone for your input. This
has been a very productive discussion for me.
I think I can conclude that the 4-20 mA
signal is not be suitable for my application. Even if I am able to
eliminate the noise or mitigate it through averaging the "range
accuracy" of the AI card is not adequate.
aeastet, I take your point that the
laser unit is probably averaging the raw data before transmitting it
over the serial port, giving the impression that the data is free of
noise. I hadn't considered this.
For future applications I will use a
rough rule of thumb that a 4-20mA signal is good for transmitting
signals with a resolution accurate to about 0.3% (0.049/16) of full
scale. My application requires an accuracy of at least 0.06%
(1/1600) of full scale which appears to be way outside the
capabilities of a 4-20 mA signal.
I can also conclude that the resolution
of a device does not imply a level of accuracy.
