O2 and CO Analysis

[Rhino]

Just in case you ever get or have gotten negative readings when analyzing O2 with a CO analyzer, here's what I learned when it happened to me. 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 in the O2.

If you have gotten negative or other weird readings when analyzing O2 for CO, what analyzer were you using and do you know anything about the reasons for the readings? If not, 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.

[hunabku]

I get -1 or -2 ppm every time I use my oxycheq CO analyzer. Not sure why.

I'm not worried about it but I don't think I'd be happy if it read -10. If it then reads 0 could it possibly have 10ppm?

[Rhino]

As you all might imagine, when I started getting -10, I broke down every testing step verrry carefully. Everything has been repeated with the same results. Breath bump testing yields -2. My 7 other tanks filled with 32% read 0 or fluctuate between 0 and -1. Both of my O2 bottles were O2 cleaned at different times in different states, but filled at the same location, which is the same location where my other tanks were filled with 32%. Both of my O2 bottles give the same -10 result. I'm confident they don't have 10 ppm CO.

[gschaut]

Is there any chance that you accidentally calibrated (zero'd) the CO detector in a 10ppm CO atmosphere?

My instruction sheet for my Analox states that the instrument must be exposed to a ZERO CO atmosphere for at least 2 minutes before zeroing the meter.

The CO meter is an electrochemical sensor that must be calibrated with each use.

p.s.: when analizing my deco tanks (80% and 100%) I always got a reading of zero (+/- 1ppm) after the meter was properly calibrated and bump tested.

[Rhino]

No chance I'm calibrating in a 10 ppm CO atmosphere.
hunabku, you always get the same minus CO readings regardless of O2 content?
gschaut, do you also get minus CO readings with your other tanks?

[ianr33]

Maybe the monitor has a semiconductor sensor? Sensor resistance goes down in CO but increases in oxygen!

http://en.wikipedia.org/wiki/Carbon_...#Semiconductor

[BUNIT]

There is a certain "model/vintage/style" of Thermo pro valve that always gives me really f'd up O2 readings (with any analyzer I have) unless I take the yoke plug out. I've ran into alot of them. No other pro valve does this. Always makes me do a double take.

[mbaker]

I have seen this with my oxycheq analyzer also. O2 seems to give me negative readings in the range of negative 6-8ppm. Get back on a tank of 32% and reads 0 to -1 or +1. I have not tried to find an explanation for this behavior but figure it is the way the sensors act in elevated O2. Would be nice if the manufacturers could provide an explanation.

[ianr33]

I have seen this with my oxycheq analyzer also. O2 seems to give me negative readings in the range of negative 6-8ppm. Get back on a tank of 32% and reads 0 to -1 or +1. I have not tried to find an explanation for this behavior but figure it is the way the sensors act in elevated O2. Would be nice if the manufacturers could provide an explanation.

Did you read the link in post #6?

[hunabku]

I read the article and seriously doubt any of our handheld CO monitors use a semiconductor sensor.

They require being heated to 400 Celsius which does not play well with pure O2.