Hi All,
We have a 200 MHz Varian Gemini 2000 which is used for our undergraduate
students. About 3 weeks back I did a He fill. The day after the fill
there was some construction going on in the Department (some serious
jack hammering) and I noticed that the flow rate was at 20 instead of
3.5-4 (which has been the case for the last couple of years). I
immediately released the pressure by opening the fill port and there was
quite a large plume of Helium that came out. After closing the valve I
kept on monitoring the drift of the field. Initially it was high (around
8-10 Hz every hour) then it stabilized to about 4 Hz every hour.
Yesteday I noticed that the flow rate was again up to 8. The line shape
looked quite unacceptable and the shims had obviously changed quite a
bit. I called up Varian and they suggested that there was a possibility
of icing inside. They also suggested using a stainless steel T to blow
He gas into the magnet. I have not done this before and was wondering if
some of the NMR gurus could shed some light. What in your opinion would
be the short term fix and what can I do as a long term fix.
Thanks in advance,
Dipanjan Nag, Ph.D.
Director of Instrumentation
Department of Chemistry
University of Nebraska-Lincoln
Received on Mon Apr 01 2002 - 09:29:50 MST