No, only minus readings I ever get are prior to calibration. Once calibrated, I get 0 +/- 1ppm on "clean" gas mixes from air to 100%. Using the Analox EIICO meter.Originally Posted by Rhino
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No, only minus readings I ever get are prior to calibration. Once calibrated, I get 0 +/- 1ppm on "clean" gas mixes from air to 100%. Using the Analox EIICO meter.
Do not go gentle into that good night.
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.
Ive been considering the analox. Do you need a bottle of calibration air that I've seen sold or is there alternative choice. I read about people using their breath but I assume thats not too accurate.
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You do not need a bottle of what is called "bump gas." Scuba gas analyzers are designed primarily to test for very low levels of CO-like anything more than 3ppm and you don't want to use that gas. You don't "calibrate" the unit and the bump gas that is sold is not intended for calibration. All it is use for is to test that the unit will respond and give an appropriate positive reading within a range. I don't use it, so I don't know what the range is exactly, but I believe the bump gas typically has 10 ppm CO and the unit should read between 7-10 ppm.
You don't need it because a breath can serve the same purpose and this was corroborated by an Analox rep. After zero-ing out the unit, a non-smoker can take and hold a breath for 10-15 seconds, then blow into the unit. The reading should be 1-2 ppm. Just what you need to see that the unit is working. If you are a smoker or someone in the vicinity of your testing is a smoker and you can get him or her to do it, the breath doesn't even have to be held for any length of time and the reading will be even higher. Also, you do *not* want to use or be near an auto exhaust or other CO source because, I believe, way high amounts of CO could damage the sensor. Remember, this is *not* a test that the unit reads X ppm accurately as X ppm, or within a certain margin for error, instead it is just a test that the unit is functioning properly by reading CO when there is even a relatively low level of CO.
After 40 years as a firefighter, I have a permenent blood CO level around 2-3ppm. I do a deep exhale into the meter, and it should read at least 2ppm if it is accurate and sensitive (operating normally). There IS commercial "bump gas" ($$$). We use it in the fire dept to calibrate our multi-gas meters.
Do not go gentle into that good night.
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.
Ya I read all that. What we have uses electrochemical sensors so keep thinking! I see reading about electrochemical that one pole uses oxygen while the other uses CO converted onto CO2. This could help explain why the readings get funky with high levels of O2?
That's interesting. Do you have a link?
I guess CO detection technology has been developed to detect CO in air rather than in pure O2, so it's maybe not too surprising O2 gives weird results.
Edit: Found this description of how electrochemical CO sensors work: http://www.nemoto.co.jp/en/column/09_ecco.html
The potential of an electrochemical cell is governed by the Nernst equation http://en.wikipedia.org/wiki/Nernst_equation it's far too late to wade through that,but yeah, if the O2 concentration changes then the voltage of the cell, and ultimately the CO% readout is going to change.
Last edited by ianr33; 09-08-2013 at 10:19 PM.
I read the electrochemical section on your link in post #6. What you have found is certainly a more in depth explanation. All I can say is that if you can make any sense of the Nerst equation your a far smarter person than that of myself. Thanks for the input.
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