OVJ Automation not acquiring
Monday, April 24, 2023
Sometimes one will see that after "Submit" the system appears to start the experiment but then silently (no error messages) quits and the experiment disappears.
The most common cause of this behavior is when the system fails to find and lock onto your selected lock solvent. The Study will start, you may see the bottom status indicator flash through "finding lock" and or "Shim...." and then go idle.
(1) First, check the lock "status". If it reads less than 1 or (even single digits sometimes), the lock signal was not found.
(2) Second, heck to make sure the "insert" toggle is depressed. There is no lock signal if the sample has not loaded.
(3) & (4) Engage the Lock Scan toggle and increase "Power" and "Gain" to maximum. If the trace shows only noise (not oscillations or a significant deviation from its 0 level), there is no lock signal being received. It sometimes takes a bit of detective work to determine exactly why.
Eject your sample!
If your sample/solvent total height* is ≤ 40 mm, it could be pushed down lower than the detection area of the probe.
| *NOTE: Indeed, the ideal sample size/volume is 40mm. Any smaller and the top and bottom edges of the liquid distort the magnetic field inside the sample even when its properly centered. Any larger and you are wasting solvent and diluting your sample. |
Alternatively, If the tube was pushed up in the spinner, it may be above the detection area of the probe.
This can happen one of three ways. One, the sample tube is so loose** in the spinner that the eject air pushes it up. Two, you accidentally pull the tube a bit when you place it on the top of the magnet.
| **NOTE: The economy NMR tubes most groups use are ~4.95 mm instead of 5.00 mm and they are not strongly gripped by the spinner's O-ring. This is compounded by finger grease being transferred from the NMR tube to the O-rings and spinner making them slick. Please use kimwipes and alcohol to clean your tubes before inserting them in the spinner. |
Three, something*** stuck in the magnet down-tube could have blocked it from reaching the probe.
| **NOTE: An empty spinner may be trapped in the magnet –usually because the last sample tube was pulled out of the spinner before the spinner was pulled out of the down tube; so the spinner drops down to the probe even with the eject air "on" Ask staff for assistance. |
One final note about spinning. Almost every NMR has some trouble with sample spinning. There are multiple points of failure and in most cases it is not actually necessary. However, "spinning" is so embedded in the system that it cannot be consistently disabled. The good news is that when trying to spin, if it finally fails, automation will continue on, the bad news is that it can take more than 3 minutes to fail.