Hi,
I am fighting with a funny effect.
Sometime the lock level of one of our spectrometers jumps
between 1 and 40% of the maximum lock level.
Sometime you can observe this here:
http://www.org.chemie.tu-muenchen.de/people/rh/status/html/pat.html
After a short investigation this was clearly due to changes
of the X shim. I got the old lock level nearly fully back if I change the
X shim current by about 300 units.
The expected failure was a faulty SCB-R. I replaced this during
this week, but this didn't really solve the problem.
As a first surprise I observed a "coupling" between Z6 and X.
If I changed Z6, this influenced the X shim. But even more
I still observe the sudden lock level changes. I believe, they are
smaller, but this might be a wrong conclusion, because this might
be a statistical effect. The observation time was not too long.
As an additional effect not mentioned yet, the lock phase changes
by 180 degree sometimes after deuterium gradient shimming.
This effect is observable for seconds or minutes and disappeares
itself.
I assume, that all described effects are due to the same reason.
One assumption is the ground plate of the shim system, which might
become wet in the past. I will look for this next time, but unfortunately
this machine is equipped with a cryoprobe. But maybe the probe itself
causes the effects described above. I never heared about this
but I wouldn't exclude it. There is a correlation between the
installation of the repaired probe and the appearance of the above
mentioned effects.
Actually I am simply looking for further ideas.
Thank you very much for every hint.
Rainer Haessner
Received on Fri Jan 27 2006 - 15:52:20 MST