Here is the promised summary to question posed wrt VT Unit stability
problems. Have not had time solve problem yet. Will post note if problem
solved.
Lawrence
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We haven't had that sort of problem, but probably the first thing would
be to isolate which part of the air system is causing instability.
You could see if its vt air by just turning the gas flow on the bvt-1000
to 0, if its too high, it could cause the sample to rattle. Turn off
the spinning air and air mounts to see if they have any effect.
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Interesting problem. I wonder what type of VT unit you have. At first I
thought maybe the field drift was messing you up but I guess it isnt.
Is the temperature gauge stable? Maybe you have too much air flow. Does
the air compressor supply air only to the supports or does it go to the
VT unit as well. Our VT-2000 works great down to 100k.
Waiting to hear how you solve it. I get multiple peaks if I forget to
turn the drift to zero.
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Perhaps you should put a pressure transducer on the air line and monitor the
system.
The transients may be not detectable with the standard gauges.
You may have a small pinhole leak or a regulator failing.
You might want to contact a Company called Vlier that I used to use.They
make a variety of anti-vibration and isolation products.I used them for
large telescope
and optical mounts and they preformed very well.
A vibration analyser will isolate your problem and help detect it's
source. Hewlett Packard has an excellent product line in this field. You
might want to contact your local rep and see if there is anyplace you can
borrow one or have it demonstrated.
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I believe your air flow is probably too high. Lower air flow is better even
though it will increase your equilibration time. I've run many temperature
studies both at very high and very low temperatures and have had no
problems with any kind of drift. You may want to make sure that your
compressor supplying the air is not cycling during your experiment and
causing the problems you are seeing.
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Most of AC-spectrometers are equipped with B-VT1000 ~ ER 4111 VT
temperature controller. Please, look for the "Instruction Manual" and open
page "VT unit, Security ampli". Find capacity C11 in the scheme and read
nominal: 47 microFarades. After that open controller and you can see that
only 4.7 uF capacity is installed. We have changed this C11 capacity to
27 uF and have no problems with temperature stability now.
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Numare Spectralab, Inc.,
10 Summit Avenue, Unit 6, P.O. Box 96,
Berkeley Heights, NJ, 07922-0096,
Telephone 908-665-0066
Telefax 908-464-4192
Name: Lawrence Byrnes
E-mail: numare@cnj.digex.net (Lawrence Byrnes)
www: http://www.cnj.digex.net/~numare/
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