We noticed that whenever the sample changer was doing something the
interference went away. The explanation was that the sample changer CPU was
regularly polling the front panel switches, and when the BACS was idle this
polling had a constant time period which generated an interfering frequency;
when the BACS was doing something IRQs were breaking into the loop changing
the time period thereby making the frequency incoherent. I believe a change
in firmware on the sample changer to vary the frequency of the switch
polling fixed the problem.
So to test this out, set your O1P and SW to zoom in on a spike, set
a short recycle delay (eg 0.1s) and acquisition time (eg. 0.5s), start GS,
enter the acquisition window (ACQU), display the transformed spectrum
(DSPPK), press the RESET button on the BACS to make it do something whilst
observing the intensity of the noise spike. If the spike changes then you
_may_ have this problem.
Cheers,
Graham
-- Dr Graham Barlow BP Amoco Chemicals 100/04, Sunbury, TW16 7LN, UK Tel: +44 1932 764236 Fax: +44 1932 762177