Hello all.

I am using a new delta plus and am struggling to find hydrogen on it
  (dual-inlet mode). I fill the bellows, and have looked for a peak with
  BDAC value around 1000; I have tried retuning the source, but to no avail.
 The instrument has been used with the precon for N2O, where it worked just
  fine. Specifically what I've done is:

  1) close SGE and look at background on cups 3,2,and 1 using B-scan (a
  little water, N2, nothing else) (I can't figure out how to do a B-SCAN
  using cups 7 and 8, which would be more useful in this case...)
  2) put Oztech standard H2 into inlet A1 and into bellows (pressure
  increases in bellows to >100) (I've tried 2 different standard bottles to
  rule out bad gas)
  3) leave source tuning as was for CO2; adjust BDAC from 10 to 3000 in
  ACON-D, INST-control
  4) I find a very large peak (>10V) in cup 7 (mass 2) at around BDAC 2500;
  small peak (0.2 V) in cup 7 at BDAC 1300; but at no point during the scan
  is there ANY change in the voltage on cup 8 (mass 3) - it stays constant at
  0.001V
  5) changed source tuning settings to match values given for old (returned)
  delta plus for HD mode (I don't have a record of source tunings used for
  HD during install); repeat step 3, result same as item 4
  6) when I get a peak (the large one at BDAC 2500 and the small one at BDAC
  1300), I've looked at the peak shape - cup 7 has a peak shape, cup 8 is
  always a flat line.
  7) I've done a baseline check to see if the amplifiers are working: the
  baselines (source off) for cups 7 and 8 are around 185, voltage readings
  are -10 and -8 (respectively). With the source on, baselines are 210 and
  185, voltage readings +8 and -8. So, turning the source on does not change
  the baseline in cup 8, but does slightly change it in cup 7. I hope this
  doesn't mean there's anything wrong with the amplifiers on cup 8... ???

  I'm assuming that I still don't have the right combination of BDAC, HVDAC
  and source settings (X1, extraction, etc.) to find the right signal. What
  procedure should I use to try to find the correct settings? I assume there
  are standard starting points, and that one simply tweaks the knobs in a
  particular order to find the right settings. Or, maybe not! Is there a mass
  calibration procedure for HD? In short, what do you do with a new
  instrument to find the HD peak?

Thank you in advance for your help,

Jonathan

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Jonathan Horton
Research Associate
Department of Biology
Virginia Polytechnic Institute
  and State University
Blacksburg, VA 24060-0406
phone: (540) 231-8713
fax: (540) 231-9307
email: [log in to unmask]

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