Monday, November 12, 2007
Testing a Magnet for Field Drift
One can test a magnet for drift by measuring a spectrum unlocked with multiple scans using a very long recycle delay. The entire spectrum will shift between scans according to the magnet drift, therefore you should have as many multiples of the spectrum as the number of scans. In the figure below, the drift rate for a 500 MHz wide bore magnet was measured. A 16 scan 1H spectrum was acquired for CHCl3 in acetone-d6 without locking. The recycle delay was 1 hour. The resonance shifts to lower frequency as a function of time. One can also see that the shim currents (either the cryoshims or room temperature shims) have drifted over the course of the measurement accounting for the broadening and multiplicity at later times.