Donghui:
I just read your ammrl message concerning magnetic pulses. We have some of
this here
too where the lock is affected and the monitors momentarily dim. We have a "hood
project" going on one floor above where arc welding is being used. This is most
certainly our cause. I discussed this recently with Peter Ziegler at Bruker and
he confirms that this is a major source of this problem. The ground leg for the
welder is the building frame, so currents are passing through the frame of
the building when a weld is made, causing field pulses in various rooms. I
would check
for any arc welding activity anywhere in your building (it doesn't have to
be closeby
to your nmr).
Jim
James E. Van Epp, Jr.,Ph.D.
Department of Chemistry
Brown University
324 Brook St.
Providence, R.I. 02912
401-863-3069
401-863-2594 FAX
e-mail: James_van_Epp_Jr@brown.edu