>Greetings,
> We keep accurate records of Helium Fills and Nitrogen fills on our
>magnets. Only one magnet lets us measure the 'actual' helium level, the others
>require us to monitor gas flow levels. Recently we had a Preventative
>Maintenance visit from the company that we have our service contract with.
>When they asked if we had any problems, I mentioned that the helium hold time
>appeared to be down. The field however did not appear to be drifting and the
>shims appeared to be stable. We agreed that I should continue monitoring the
>magnet.
> Well, as you can guess the magnet quenched three weeks later.
>Fortunately, or unfortunately, it occurred over the weekend. I am not sure
>what could have been done to prevent the magnet quench but the important lesson
>is that the magnet boil off rates and hold times should be carefully monitored.
> Looking at our log we realized that the hold time had been slowly decreasing
>for a number of months, but only during the past couple of months had it been
>so dramatic as to be noticeable.
> I have reviewed the logs of the other two magnets and they seem to be
>behaving normally. The bottom line is that one should spend a few minutes
>reviewing the log books for five or six months to determine if there are
>problems with the magnets.
>
>Bob Dudley
>Proud Owner :-( of a quenched 300 widebore magnet.
>
>
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Hongjun Pan, |Ph. D. NMR Spectroscopist |
Department of Chemistry |(409)845-8993 |
Texas A&M University |(409)845-4719(FAX) |
College Station, TX 77483-3255 |pan@chemvx.tamu.edu |
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