For what it's worth, the only times I have seen an oscillating lock signal
was when the lock power was too high. Since this happened after a fill,
could there be a blockage or oscillation in the N2 boiloff lines?
On Mon, Jan 8, 2024 at 12:42 PM Kenneth Sharp-Knott <kknott_at_vt.edu> wrote:
> There appears to be more at work here than originally thought...
>
> I believe this all started after a routine refill of the Prodigy N2
> dewar.
>
> Shims are terrible. Far worse in D2O with very broad lines. The
> Lineshape standard will sometimes meet specs, but samples in D2O are
> consistently bad. This is both with topshim and after attempting to
> manually correct the shims.
>
> I have 3D shimmed repeatedly. This system, an Avance II 500MHz, generally
> needs convection compensation. My usual topshim sequence has been 'topshim
> convcomp ordmax=6 tuneaz'.
>
> The Bruker engineer took a look remotely and didn't find evidence of a
> dirty probe or cracked insert. He suggests the issues are related to an
> oscillating lock level and blames the oscillation on convection. He
> suggested a blockage in the VT gas. I have traced the line and there is no
> blockage, kink or break in the line. I have removed the line and can feel
> VT gas flow which in increases and decreases normally with the VT Gas Flow
> setting.
>
> By lock oscillation, I mean that the lock level will be steady and then
> increase or decrease 5-10% over a maybe 20 seconds and then stabilize.
> This happens repeatedly to varying degrees.
>
> Does anyone have any suggestions for a cause for this lock oscillation?
> Video attached. Lock is ON.
>
> 30mg Sucrose in D2O - red is usual - blue is current state.
>
> Lineshape Std 0.3% Chloroform in Acetone
>
>
> Ken Sharp-Knott
> Manager of Analytical Services and the NMR Facility
> Department of Chemistry
> Virginia Tech
>
> (540)267-6502 (Cell)
> (540)231-0885 (Office)
>
>
>
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Received on Mon Jan 08 2024 - 10:04:11 MST