The following table is used to record weekly (7-10 day) nitrogen fills for the NMR.
The actual table is printed landscape on 8.5" x 11" paper with sufficient space in the columns to cover the 11" portion of paper and enough additional rows to fill the 8.5" section of paper.
Multiple copies of the table have been placed in a binder titled "Liquid Nitrogen Fill Log" that stays in the NMR room.
The all columns are filled out by me on the day I perform the liquid nitrogen fill.
NO LONGER NECESSARY WITH MOVE TO NEW BLDG (A predrier, installed for the air supply, is vented daily (using a series of timers and a solenoid switch) and the weekly accumulation of water/oil is measured and entered in the "Filter mL" column.)
The room temperature, NMR field, helium vent rate, and % liquid helium are recorded weekly.
The portable liquid nitrogen dewar provides up to three fills of the NMR magnet dewar and the "Fill #" column represents the current fill number from the portable dewar. This has provided data to recognize problems with the portable nitrogen dewar (e.g. incomplete fill or abuse by the cryogen distributor).
The nitrogen level of the magnet dewar is measured using the thumping rod and both the starting and ending depths (in cm) are recorded each week.
Each fill is timed, including the time for each turn of the fill knob on the portable dewar (up to 3/4 full turn max); generally I fill for 4 minutes each at 3/8 and 1/2 turn of the fill knob, then after the fill is complete at 3/4 full turn of the fill knob, I turn it back to only 3/8 turn open in order to "top off" the magnet dewar.
The last column is checked-off only when the fill-port cap has been reattached to the top of the nitrogen fill tube on top of the magnet. This ensures that this cap is not left off, which would lead to icing of the nitrogen fill tube leading down into the magnet dewar.
I was strongly encouraged by my predecessor to include the back-up checker columns and the nitrogen fill cap column to the log sheet; I no longer utilize the back-up checker, although this is a good idea.
NITROGEN FILL LOG SHEET
Begin Date _______________ 20____ End Date_______________ 20____
Date |
Day |
ID |
Room |
NMR |
% He |
He Vent Rate |
# Days Between Fills |
Fill # |
Start cm |
End cm |
Total min |
.375 t min |
.50 t min |
.75 t min |
N2 Cap |
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Liquid Nitrogen Fill Procedure