Stable Isotope Geochemistry


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Ethan Goddard <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Thu, 5 Feb 2004 14:30:28 -0500
text/plain (100 lines)
Hello again isotopers,

I'm still having trouble w/ my CE NC2500 - no sample CO2 peak elution.
I've tried or tested all of the suggestions that were made after my
first post a few days ago including

- testing and replacing the O2 circuit solenoids (EV1 and EV2,
originals did not measure as shorted - both were in the 550 Ohms range
which by my calculation was right - 24V, 1W)
- confirmed O2 flow through O2 loop circuit and out purge.
- trying the "match test" (no oxygen flare-up at the carrier-combustion
tube junction)
- making sure that retention times were not an issue (removing the N2
peak jumping to focus solely on CO2).
- jacked up the combustion temp to 1020 and 1050 to see if we we just
below the flash combustion threshold
- going "back to basics" confirming flow rates, purge rates, carrier
pressures, temperatures, timing, etc.

In light of the failed match test and new solenoids I turned my
attention to the electronics.  I measured the voltage across the two
contacts of each solenoid plug EV1 through EV5.  When energized they
measured ~17VDC.  The solenoids themselves are spec'd to 24VDC and the
PS1110 PCB is a 24VDC supply board so I'm wondering if I've got a power
supply problem.  Can anyone confirm that the supply voltage to the
solenoids needs to be 24VDC or should 17VDC be sufficient to switch
them on or off?

Also, does anyone have a pdf, or scan-able schematic for the PS1110 and
EVDV boards?  I'd like to take some readings on the test points to make
sure that the boards are functioning properly but I don't have the
drawings.  If someone would be willing to xerox or scan me a copy of
theirs I'd be grateful.

Any and all suggestions are appreciated.


Begin forwarded message:

> From: Ethan Goddard <[log in to unmask]>
> Date: Wed Jan 28, 2004  12:06:15  PM US/Eastern
> To: isogeochem <[log in to unmask]>
> Subject: replacement for Carlo-Erba NA-2500 O2 solenoid valve?
> Greetings isotopers!
> In short, Iím looking for a replacement, or alternate supplier, for
> the O2 solenoid valve for a CE 2500 EA (I believe itís EV2 on the
> pneumatic schematic).  Lead time from the OEM valve manufacturer (FAS)
> is 4-6 weeks and I frankly would like one a bit quicker.  Has anyone
> found a suitable replacement for, or an alternate supplier of, these
> valves?
> As best I can tell the spec on the FAS valve (p/n 01-311P-01-H0) is
> 3-way, direct acting, normally closed
> 0.8mm orifice, 0-8 bar range
> Any help would be greatly appreciated.
> And now for the long versionÖÖ
> Hereís the problem that Iím trying to solve, if Iíve overlooked a
> possible solution Iíd be grateful to hear about it.
> -CE 2500 EA coupled to DeltaXL MS
> -N2 and CO2 reference peaks look great (raw ratio, peak height/shape)
> -N2 sample peaks look good (elution time and peak shape)
> -NO CO2 sample peak elution!!!
> -Hereís what Iíve done so far
> -Check O2 circuit (pressure and flow are ok, 24V signal across
> solenoid triggers ok)
> -Extend run time 3x original CO2 elution time to see if thereís a
> wicked bad flow restriction
> -replace reactors and traps (combustion, reduction, h2o)
> -baked GC column 150į 12 hrs
> -replaced GC column, no change
> none of these steps has resulted in any change.  Iím left to conclude
> that Iíve got pyrolysis generated N2 coming through and no combustion.
>  Iím thinking that either EV2 or EV3 is failing to switch over and
> reroute the O2 loop volume through down sample path.  Hence, Iím
> looking for readily available replacement valves for the O2 circuit.
> Thanks,
> Ethan
> Ethan A. Goddard - USF College of Marine Science
> 140 7th Ave. S        St. Petersburg, FL 33701
> 727-553-1017(lab)     727-553-1189(fax)
> [log in to unmask]