Get the Thermo people back out and make them put their instruments to
specifications that are reasonable. I am hearing more about sloppy C-
service than not.

Marilyn

> Hello All,
>
> We are experiencing some persistent problems with our Delta XP.  We had it
> serviced a few weeks ago by Thermo (Source cleaned, pump oil changed etc.)
> and now we can't get it back into spec.  The linearity for all reference
> gases is poor and fails spec every time (increasing the pressure of the
> ref
> gas changes the isotope ratio significantly) but the precision/stability
> is
> very good with std devs across 10 on/off gas pulses being in the region of
> 0.03 per mil or better for both carbon and oxygen measurements of carbon
> dioxide.
>
> We tried
> *
>
> 	replacing the filament in the old source,
> *
>
> 	further cleaning the ceramics,
> *
>
> 	and have recently changed the source for an entirely new one, but
> this hasn't fixed the original problem.
> *
>
> 	We've purged the gases through the conflo,
> *
>
> 	and blanked off the dual inlet side of the instrument...all without
> success.
> Our linearity for carbon in CO2 at the moment isn't as bad as it has been
> and is around 0.1 per mil per volt for carbon measured across a 10 volt
> range (but outside the spec of 0.066 per mil per volt).
> Prior to the service we commonly observed excellent linearity - for CO2
> consistently better than 0.06 per mil per volt.
>
> We had a problem with the electronics (source board) a while back and had
> this replaced, so in theory that should be fine....measuring the voltages
> off the board didn't reveal any problems.
>
> I've seen some of you have had similar problems before and wondered if you
> have any more ideas? Any suggestions would be very gratefully received as
> we're rapidly eliminating possibilities.
>
> Thanks in anticipation for your help,
> Claire
>
> Claire M Lock
> Forensic Researcher
> T: +44 (0)1959 892180
> F: +44 (0)1959 892656
> E: [log in to unmask]
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Dr. Marilyn L. Fogel
Geophysical Laboratory
Carnegie Institution of Washington
5251 Broad Branch Rd., NW
Washington, DC 20015 USA
Phone: 202-478-8981
FAX: 202-478-8901
Website: http://fogel.ciw.edu