we have a problem with unstable sensitivity on our Delta plus. During 12
hours the signal drops down from 4500mV (m/e44) to 1300mV. When we refocus,
we only have to turn the potentiometer "symmetry" and get the previous
signal back. It is sufficient to change the potentiometer-position from 7 to
3 and back when the drop of sensitivity occurs again.
Sometimes the machine is stable for several days and in other cases the
signal drops (or sometimes rises) during hours.
We have cleaned the source and changed the filament and the source-magnets
with no effect.
Our electronic-workshop checked the potentiometer "symmetry" ok. We measured
the adjusted voltage on the potentiometer. It stays at 104,7V although
sensitivity drop occurs.
Does anybody have any idea what the cause might be?
Dr. Jens Dyckmans
Centre for Stable Isotope Research and Analysis (KOSI)
University of Göttingen