Hi, Wei:
Your situation is not too bad. We have an exactly same magnet as yours. Ours
drifts 9 - 10 Hz per hour. According to Varian's specifications, the magnet
drift is 10 Hz/hr. So nothing can be complained, because it's just passed
the specification. What you can do is that to change the lock frequency
every three months.
By the way, our other four magnet drifts are about 1Hz/hr or less.
Have a good day.
Yuyang
Yuyang Wu, Ph.D.
NMR Specialist
ASL, Chemistry
Northwestern U.
2145 Sheridan Rd.
Evanston, IL 60208
Phone: 847-491-7080
Fax: 847-491-7713
-----Original Message-----
> From: Wei Li 448-7532 [mailto:wli_at_utmem.edu]
> Sent: Monday, April 02, 2001 4:43 PM
> To: ammrl_at_wwitch.unl.edu
> Subject: magnet drifting
Hi Friends,
We had an Inova-500 installed last July. The magnet is actively shielded. I
measured the drifting rate recently, it is always around 5~6Hz. The lock z0
drifted about 400 Dac unit a day. According to Varian and my own
measurement, 3 Dac unit in lock z0 value corresponding to ~1Hz in proton
frequency. In view of this value, the big lock z0 drift is not that
unexpected (5Hz/hr * 24hr/day * 3Dac/Hz =360 Dac/day).
The service manager of Varian claims that it is not a big deal, but I don't
feel comfortable. This kind of drifting would quickly make macros such as
setlk (although I am not using it)useless, since the lock z0 for a solvent
will drift thousands of Dac unit away in a week.
I ask some of you during the ENC, and no one seems to have such a
substantial drift in lock z0 in their systems. Even the drifting rate is
1Hz/hr, in a month the lock z0 should still drift more than 2000 unit a
month, is that true on your system?
So I need help from you, particularly who have Oxford AS magnet and Inova
console:
1. Do you have such a drifting problem with your magnet and lock z0?
2. What is the big consequence, besides resetting lock frequency about
every 4 months (the drifting value will exceed 32k during this length of
time)?
3. What is the typical lower limit for proton frequency when the bandwidth
of the filter becomes a problem, and we have to recharge the magnet? Right
now, our proton frequency is 499.73MHz.
Any suggestions will be greatly appreciated.
-----------------------------------------
Wei Li, Ph.D
Dept. of Pharmaceutical Sciences
University of Tennessee HSC
847 Monroe, Room 327
Memphis, TN 38163
Phone 901-448-7532 (Office) Fax 901-448-6828 (Office)
Phone 901-527-6784 (H)
Received on Fri Apr 06 2001 - 08:56:20 MST