Looking at your system location via Google Maps, it seems to support the likelyhood that the streetcar is responsible for the field jumps you are seeing, in conjunction with not-so-good magnetic opacity of your older magnet (i.e. how much your magnet is attenuating external magnetic field changes).
While it is impossible to remote-diagnose this for certain, I am seeing that you are located in the center of a loop formed by the tram line, and would think that you might even be able to directly correlate the portion of the tracks that a streetcar needs to be on in order for the field to fluctuate.
I would also think that you will be able to observe the same frequency behavior on all the other magnets as well, just significantly attenuated by 1-2 orders of magnitude and therefore easy to miss. You would need to run synchronized experiments on each system with sufficient resolution to confirm this. I am pretty sure that your magnet manufacturer would be able to predict the approximate frequency fluctuations based on the 300 MHz performance and the specific magnet opacity characteristics that only the manufacturer would know.
If you need to run unlocked, this article here might be helpful:
Efficient compensation of low-frequency magnetic field disturbances in NMR with fluxgate sensors. <
http://dx.doi.org/10.1016/j.jmr.2005.02.018>
Best Regards,
- Knut Mehr
> On May 29, 2015, at 5:00 PM, Ron Crouch <roncrouch1_at_mac.com> wrote:
>
> In a previous life I once traveled to Paris to sort out similar issues in a lab with a 500 and 600 sitting beside each other. The 500 was fine and the 600 behaved badly in a fashion similar to what you describe. The subway ran under the building so it was the likely culprit. After a few false starts it was found that a nearby FM radio station switched power massively with a schedule close to the subway.. midnight power went down 6 am back up. Our problem was the lock frequency in the 600 matched the radio station! Better shielding on the VT setup fixed the issue.
>
> Since you see issues with lock off I doubt a similar case in your case but thought the mystery story worth repeating. Best luck with a solution and please let us know the answer!
>
> Best,
>
> Ron Crouch
>
> On 5/29/2015 2:17 AM, Christophe Farès wrote:
>> Dear AMMRLers,
>>
>> I've seen some amazingly fast and helpful crowd-problem-solving on the AMMRWe oneL network lately, and so I thought I would share my own issue hoping for a similar response ;)
>>
>> We have a relatively newly installed AVIII Nanobay 300MHz system (with an older ultrashield magnet) used in open-access for routine 1D NMR. The 2D experiments are however plagued with horrible T1-noise streaks and we identified some major field instabilities as the most probable source of the problem. If we run a 1D 1H continuously without lock, we see erratic field jumps of up to +/-30 Hz! Curious however is that this phenomenon does not seem to occur completely randomly. For instance: it seems that there are periods of 5-8 minutes every 25-35 minutes where they are more intense. And nights between approx 11pm and 4am, the interferences are almost completely gone. To illustrate what I mean, I've attached a printout of the 2d stacks (each column represents 2048 1D 1H measured every 2 seconds)...
>>
>> This is not observed on 400, 2x 500 and 600MHz spectrometers sitting only a few tens of meters away.
>>
>> Of course, the night relative calmness and "regular" more intense periods made us look into public transport schedules. The closest streetcar stop is 400m away, but the schedule correlates quite wellwith this phenomenon (for instance, the first one runs at 4:30, intervals are 20-30 minutes).
>>
>> So my questions are: what could be causing these disturbances and how? And of course, what can we do about it?
>>
>> best regards
>>
>> Chris
>>
>
> --
> Ron
>
Received on Sat May 30 2015 - 14:45:34 MST