HI Ken
it looks like you now got about 0.3 degree over your sample based on the 59Co information.
What is your airflow setting? if it is 535 l/h you can easily set it to 640 l/h and this
will reduce the temperature gradient further.
The BVT3000 has a bank of valves to set the airflow. The different flows are generated by
combinations of them being open. The flow rates are not including any back pressure from
all the parts between the valves and the probe. This means at the probe you have quite a
bit less flow.
Our latest generation of instruments uses massflow controllers to regulate
the gasflow. This means you get the requested flow irrespective of backpressure.
Regards
Clemens
On 1/12/2024 1:44 PM, Kenneth Sharp-Knott wrote:
Topline: Bruker was right from the beginning. The issue was a problem with
the VT gas flow stemming from a malfunction in the BVT3000.
After replacing every inch of tubing to the console and from the VT unit to
the probe trying to find a leak, blockage or kink, I noticed that the float ball
in my BVT 3000 did not drop when it was turned off. Fortunately, I have lots of
old instruments with BVT3000's and swapped them out.
Turns out the old unit was obstructing the flow in some way. The flow did
increase/decrease, but was evidently less than 100%. I was unable to tell a
significant difference but clearly, there was one. First clue after replacement
was that the power required to regulate at 25C went from 1.1% to 0.5%.
After replacing the BVT 3000 and redoing 3D shims I was able to get excellent
lineshape and my D2O samples look excellent. As to the Co59 sample, it still
looks a little misshapen, but I'm getting 50Hz instead of 3-4ppm. Not perfect,
but likely better than it's been in a long time.
I should have probably caught this sooner, but the BVT3000 seemed to be regulating
the flow.
On another note, I think it would be nice to get a flow meter from these kinds of
flow rates. Any suggestions? The only ones I have found are for much lower flow rates.
Thank you all for eventually getting me pointed in the right direction. I've learned
a ton about VT, temperature gradients, convection, Co59 and many other things that
I will employ in the future!
--
Ken Sharp-Knott
Manager of Analytical Services and the NMR Facility
Department of Chemistry
Virginia Tech
(540)267-6502 (Cell)
(540)231-0885 (Office)
--
==========================
==========================
====================
Clemens Anklin Ph.D. Vice President
Bruker BioSpin NMR Applications & Training
15 Fortune Drive NEW Phone: 978-313-5NMR(5667)
Billerica MA 01821 twitter: _at_canklin
web: http://www.bruker.com
e-mail: clemens.anklin_at_bruker.com
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Received on Sat Jan 13 2024 - 06:20:24 MST