Stable Isotope Geochemistry


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Howard Sanford <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Wed, 11 Feb 2004 12:32:56 -0500
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My Delta Plus is currently in the semi-dreaded no signal in second cup
state. I know how to get the signal back. Either start a run with no peak
center, or just restart the software. Either of these will re-initialize
the hardware and get the signal back. Simply turning the source off and on
will not get the signal back. However, I'd really rather study the
situation and try to figure out exactly what is happening, as I have no
critical samples right now, and this has happened twice within the last 50
samples I've run. How can I check the actual output from the detectors? The
detector board stat? What should I even look at?

Perhaps I should give you some background on my system and what I've done
and noticed so far.

My system is a Delta Plus, GPIB interface, installed 2000. I have 5 cups
(don't ask), 1 and 2 are both narrow and seldom used. My universal cups are
in positions 3, 4 and 5. Standard wide narrow wide configuration.
Continuous flow only. Originally had 2 Conflo II's, control selectable by
an external manual switch. Recently added GasBench/Precon. Initially it was
a NT 4.0/ISA GBIP system. Currently XP/PCI GBIP ( I know, not supported,
but seems good so far). I've lost signal in the second cup at the beginning
of a run with Iso NT 1.2, 1.5, and now 2.0, 4 different software installs,
2 different computers, 3 different GPIB cards (2 ISA and one PCI) and 3
different OS installs (NT4 FAT32, NT4 NTFS, and XP). As has been stated by
Finnigan themselves, this appears to be a MS hardware problem, not software
or computer/interface hardware. After the last bout of posts on this
subject and Gilles excellent computer setup procedure, I decided to
'rebuild' my NT box from the ground up. Seems like it couldn't hurt and if
he had never seen this problem with all the systems he has I figured it was
more than worth a try. Maybe there really is some software/computer connection.

I had many spare parts, so I pulled the original hard drive out of the
original computer that came with the instrument (Gateway E4200 PIII 450).
This had REAL/32, NT 4.0 SP 5, and had seen ISODAT 7.5, Iso NT 1.2 and 1.5,
SP 1.7. It was also FAT 32. Rather than reformat this, I put in another
hard drive (not new, but compleletly wiped) and started fresh with NT 4.0
installed with NTFS. This would also allow me to instantly go back to my
old semi-stable system by simply swapping hard drives if necessary. This
system was prestine. ONLY Finnigan's software, Isodat NT 1.5, SP 1.8. No MS
office, no network (while running the instrument), no other applications.
Even managed to find the correct Intel IDE bus mastering drivers, which
even Gateway hadn't installed on the original system. Installed EVERY NT
update (I had to reboot about 20 times to get everything!) as of Nov 2003.
At the time I only had the original 8-bit ISA GP-IB card, so I used this.

This system seemed stable, though during the install of my GasBench and
Precon in Dec, it lost signal in the second cup (cup #4) during a GasBench
run. Well, this had happened every 500-1000 runs, so I just took it on the
chin. Then 3 weeks ago during a Conflo/EA sequence it happened again, about
only 200 runs later. Again, maybe just a fluke, and I really needed to
finsh, so I restarted the software, reweighed the lost sample and kept going.

Then this last week I had a chance to try an XP box with a PCI GPIB card
(National Instruments 2.1 XP drivers) and Isodat 2.0, sp 1.35. Everything
seemed to be going fairly well. Ran several std on-off sequences, both with
the GasBench and a Conflo, and had no problems. The I start a regular
EA/Conflo sequence. On the second sample, the middle cup went dead. I
stopped the run before it wasted my EA sample, and now that's where I'm at.
The software returned no errors. This was a nitrogen only run, and I long
ago abandoned peak centering before every run for nitrogen only sequences.
If the cup gets 'lost' and you try a peak center, it stops the whole
sequence with the error peak center not found. If you don't have to peak
center, the sequence will continue, and you only lose one sample. As I
said, with the next hardware initialization the signal will come back.

Oddly, one thing I have encounted is that if I'm doing Carbon only runs,
the signal tends to be lost after the peak center. The time I lost signal
with the Gasbench and the next time on the EA I was running carbons, and I
do peak center for those. I wasn't watching the peak center, but the file
recorded finding a normal peak center, but then proceded to only acquire
cups 3 and 5. Every time I've seen this happen with nitrogen, it gets lost
before the peak center, and the sequence aborts. A clue perhaps?

Another thing I've noticed is that this is happened more (3 times since
December) since I added the GasBench and Precon than it has for the last 2
years with only Conflos. Another clue?

Anyway, if anyone made it this far, thanks for your attention.


Howard Sanford
North Carolina State University
Dept. of Soil Science
Box 7619
3114 Williams Hall
Raleigh, NC 27695