>Hi
>I have found the same periodic fluctuations, which occur as a sine wave.
>Have had no explanation from Europa regarding it, so it's a mystery to me
>also. Let me know what you find out. I also have a 20/20 coupled to
>ANCA-SL.
>
>kris
>
>
>
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I had the same problem at the University of California, Riverside,
when I was there.  The period was about 20 minutes.  The source of
the problem was traced to the laboratory air conditioner, which
cycled on and off every 20 minutes or so and blew directly on the
collector electronics housing.  The solution was to place a blanket
over the collector housing--a K-Mart "blue light" special did the
job nicely for $5.  It was thought that the relatively large change
in resistance with temperature of the ion beam electrometer feedback
resistors was the culprit.

Tyler Coplen