Hi Carl,

I’m having a similar stability problem as Evan and also just ran with a CO2 trap, although the problem developed after I switched back to the water trap.  Are you suggesting that the CO2 trap might be causing the instability?

Bye for now,

Jennifer McKay
Assistant Professor (Senior Research)
Stable Isotope Lab Manager
CEOAS, Oregon State University
Corvallis, Oregon 97331

On Jan 16, 2018, at 8:28 AM, Carl Johnson <[log in to unmask]> wrote:

Hi Evan,

I'm not sure about your noise (it does look electrical to me), but in reading your post something else caught my eye that I'd be careful of.

Specifically, the use of a water trap *upstream* of soda lime trap might be counterproductive. I have a recollection of a soda lime trap not working when it dried out: the reaction relies at one stage on the dissolution of CO2 into a wet layer at the surface of the soda lime pellets.


On 2018 Jan 16 11:02, Evan Baker wrote:
Hello all, can anyone help us diagnose this issue?

We're seeing cyclic noise in the signal coming from our Delta Plus XL.

The noise is in the form of a voltage drop at regular intervals (every few seconds). The size of the voltage drop increases as the signal intensity increases. All of the cups have this issue, although the size of the voltage drop is different for each one and seems to move from cup to cup. The noise is present even with the Delta closed off from the EA.

Our setup: Carlo Erba NC2500 --> Conflo II --> Delta Plus XL

Here are pictures of the bad signal:
Scan results: http://tinypic.com/r/63vhp1/9
Reference N2 results: http://tinypic.com/r/262wnbo/9
Zoomed in: http://tinypic.com/r/28qwz60/9

The regularity of the noise makes us think this must be an electrical issue. However, we first saw this problem after adding a CO2 trap to the EA. We used soda lime as the absorbent and placed the CO2 trap between two water traps. The coincidence of the trap change and the noise makes us think this could be a contamination issue. The CO2 trap has since been removed, but the issue persists. To make things more confusing, the noise will occasionally disappear completely and the system will be stable for a few days at a time.

We greatly appreciate any suggestions!

-Evan Baker
Laboratory Manager
Stable Isotope Laboratory
North Carolina State University

Mr. Carl G. Johnson
Research Specialist
Dept. of Marine Chemistry and Geochemistry
123 Fye Laboratory, MS#4
Woods Hole Oceanographic Institution
Woods Hole, MA 02543-1543

Tel:  508-289-2304
Fax:  508-457-2164
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