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noise in the PAM fluorometer

ABarnet abbarnet at dal.ca
Wed May 26 10:40:08 EST 2004

Help please!

I am having serious problems with noise in a PAM 101/102/103
fluorometer (Walz).  The normal noise in the signal ranges about +/-
0.015V measured at 1.6kHz with the gain/damping/etc settings I'm
using.  This goes through a strange low-frequency sinusoidal pattern
in the signal followed by an increase in the noise to +/- 0.20V
measured at 1.6kHz.  The signal then can either remain noisy, or
slowly decrease in noise back to a normal level on a time scale of
30min to hours.  This noise comes and goes unpredictably and I can not
do anything to induce or get rid of it (ie. wiggle conntections, find
breaks in wires, bad grounds, etc.).

Has anyone seen this problem before or had similar problems with their
instrument?  Any insights?

I have ruled out the posibility that it is stray light into the
photomultiplier detector.  Also, analysis of the output shows the
signal noise is not at a frequency of 60Hz, so I am assuming it is not
electronic interfearence, but I have not totally ruled that out.  I am
in the process of doing things like replacing the BNC cables and
trying to make sure everything is shielded.  I have also verified, by
hooking up a chart recorder, that the output to the computer is what
the PAM is telling it.

Thanks for your input!

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