Dear David,

I've been through a similar experience with my DeltaS while working
at the University of Heidelberg. Not only were isotope ratios T
dependent but my peak centre moved with changing temperature which
even affected dual inlet measurements. In fact, the peak centre
change with temperature was so reproducible that I could tell the
room temperature without consulting a thermometer (after plotting a
calibration graph just for a laugh).

First solution was to draft insulate the analyzer array, remove back
and front panels, and then place a 20" blade oscillating fan at the
back of the instrument. Eventually, The University agreed to move my
instrument in a spec built room (air conditioning plus humidity
control, the works).

In contrast to Europa Scientific instruments (safe the Hydra) all
Finnigan machines use an electro- magnet and, hence, a magnet current
controller. These are the most T sensitive parts in a DeltaS. Even
the oscillating fan solution could not prevent the early demise of
one magnet current controller.

After relocating into the new climate controlled lab everything was
fine on the T front. Everything except the fact that we were now at
the end of power supply line, i.e. behind lifts, X-ray dept.,
kitchen, sterilisator unit. Now isotope ratio were dependent on the
time of the day and the instability of the supplied voltage (at times
below 200V instead of the required 230V). Just by looking at the CO2
background and the 45/44 trace I could tell when which unit in the
Children's Hospital started to work.

So, solution number two: routing our power supply from another
distribution point where we were the only user.

Anyway, for your temperature problem you will have to bite the bullet
and fork out some monies for a good climate control unit (air
conditioning without humidity control might work but you are apt to
end up at either extreme point humidity-wise, too dry or to humid
neither of which the instrument takes too kindly to).


All the best,
                          Wolfram




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Dr. W. Meier-Augenstein
Lecturer/Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
Small's Wynd, DUNDEE  DD1 4HN, United Kingdom

Tel.: +44-(0)1382-34/5124, /4968
      +44-(0)468 -314563
Fax:  +44-(0)1382-34/5514

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URL: http://www.dundee.ac.uk/AnatPhys/wma/wolfram.htm
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