Odd Results with CO Analysis

[Rhino2]

Just in case you ever get or have gotten negative readings when using a CO analyzer, here's what I learned when it happened to me. I'm posting in this forum in case anyone else gets similar results analyzing something other than pure oxygen. If a moderator believes this should be posted instead to another forum, please move as you see fit.

According to Patti from Analox, since the reading was a negative reading (-10 actually) and it's obvious that the analyzer wasn't reading a deficit of CO at 10 ppm, I could treat it as effectively no CO. Of course, that advice only came after she interrogated me to determine that I was properly using the analyzer.

If you have gotten negative or other weird readings when using a CO analyzer, for O2 or any other gas, what analyzer were you using and do you know anything about the reasons for the readings? If you've never gotten negative readings, especially with O2, I'd be interested to know what analyzer were you using.

FWIW-It appears that suspected causes are related to the valve, either the solution used to O2 clean it or the O2 compatible lube, and the solution used on the inside of the tank during the O2 cleaning process. My question remains, why didn't I get the negative readings with other tanks that are truly 100% O2 clean, but are routinely filled with 32% nitrox?

 

[knotical]

It also calls into question the algorithm design, and the analyzer itself. I would not use that analyzer again. If it reads -10 when it clearly can't be below zero, what's to prevent it from reading zero when the actual is +10?

 

[ianr33]

What principal do CO monitors work on?

 

[Rhino2]

knotical, what CO analyzer do you use and what results have you gotten with 80%-100% O2 and lower %'s of O2?

In answer to your question, the zero reading in room air, the +2 reading with a breath bump test, and the zero to +1 readings when testing other tanks, I believe, all "prevent" the analyzer from reading zero when the actual is +10. I don't know whether you'll ever have an opportunity to use my CO analyzer, but given those results, along with consulting the manufacturer on this specific point, and the quality of the Analox O2 analyzer (including the one I have been using for more years than I care to mention) and the company, I'm confident my O2 has no CO. And, "no" I am not trying to curry favor with Analox-I did my research like most of us do, paid retail for my products, learned how to use them, use them, and called for support when I have needed to over the years.

 

[knotical]

knotical, what CO analyzer do you use and what results have you gotten with 80%-100% O2 and lower %'s of O2?

I don't have a CO analyzer. I have used some belonging to others. I was speaking primarily from my experience with a variety of instruments in a variety of industries during my times as a technician, scientist, and engineer. When any device gives a clearly bogus result, it becomes suspect. If there is not a clear and compelling explanation of the -10, then your other checks and balances instill less confidence than they might otherwise. Perhaps you could get a similar instrument and run side-by-side comparison tests.

 

[ianr33]

Seems your CO monitor might have a semiconductor sensor:
"Oxygen increases resistance of the tin dioxide while carbon monoxide reduces resistance. The integrated circuit monitors the resistance of the sensing element." In which case CO will give a positive reading, but oxygen would give a negative reading.

Carbon monoxide detector - Wikipedia, the free encyclopedia

 

[MB2013]

At work I have to analyse CO/CO2/02 readings. C0 is either present meaning 1ppm or greater or its not present. You don't get minus C0 readings. I would get the Analyser looked at by Analox if possible or a local service centre. I was thinking about buying an Analox CO Analyser myself. I would appreciate if you could post the outcome on this thread.