Dear BUMers,
I should review the solution of my question posted a few months ago
concerning the VT stability.
The solution was rather simple:
Proper setting the spectrometer input reducing valve. There was fluctuation
of pressure in the VT unit, which caused the temperature fluctuation.
Since our compressor produces pressure in the range 5-7 bar (which is a
little too low), the reducing valve must be set somwhat below this range.
After a few months I can say that even pressure as low as ca. 4.5 bar is
sufficient tu run the spectrometer.
For me it is still mystery, how the spectrometer could be working several
years in the same set up without problems (or who could change setting of
the reducing valve).
I have collected suggestions of Jeff de Ropp, Phil Denison, Carl Bridge,
George T. Furst.
In addition Michael Engelhard was right that it was not a software problem.
Many thanks to all.
The original question is in the bottom.
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Carl Bridge:
Your problem maybe due to a low gas flow to the probehead. Can you confirm
that the flow at the input of the probehead is OK!. Maybe there is a fault
with the flow control valves within the BVT or possibly a kink in the tubing
somewhere inside the console or the loom of cables to the probehead. You
should try using different gas flow settings in the EDTE window as this will
bring in different valves and may show that one of the valves is faulty.
There are 4 valves inside the BVT which when used in different combinations
achieve the different gas flows. The table below may help you to find which
valve is not working.
Decimal combination Combination ABCD Flow rate (l/h)
0 0000 0
1 0001 135
2 0010 270
3 0011 400
4 0100 535
5 0101 670
6 0110 800
7 0111 935
8 1000 1070
9 1001 1200
10 1010 1335
11 1011 1470
12 1100 1600
13 1101 1735
14 1110 1870
15 1111 2000
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Phil Denison
Is 'adaptive tune' turned on in the edte 'Control' menu? I have found
problems if it is not turned off.
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Jeff de Ropp:
We had a similar problem and fixed it by replacing the probe heater. I know
that sounds unlikely but that's what solved the problem for us.
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George T. Furst:
I have seen similar problems on our Avances it is usually corrected by
replacing the Eurotherm in the VT unit . On one case it was caused by the wt
of the air pulling the probe dewar down a bit so that air flow was not very
efficient.
>Dear BUMers,
>We have a problem with stabilisation of temperature using BVT 3000 on
Bruker
>Avance 500 system.
>It was working nicely about 8 years.
>The problem is:
>Arrival to the temperature set in "edte" has become very slow. Usually,
>"self-tuning" the feedback loop fixed this in the past, but it does not
help
>now, no matter what actual temperature is set.
>In addition, in the medium-run (say minutes), we see +-0.1 K fluctuation
of
>sample temperature and accompanied variations in heater current.
>We see the problem on two probes with different thermocouples (T and
>BTO2000), so it is not related a particular thermocouple nor to the wire
>connecting the thermocouple and the BVT.
>To me, it is seems rather as a sofware problem, that the "self-tune"
routine
>does not work properly or the BVT unit does not accept the results.
>Did anybody observe anything similar? And better, does anybody knows the
>solution?
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