What is Minus 3 ppm of Carbon Monoxide

You are probably right, the zero air was not completely scrubbed of CO or your detector circuitry may not be calibrated properly.

horace40,

-3 PPM of CO, or of anything else, IS a philosophical concept...

Did you "test" the ambient air?

With respect to "the super dry air from the purifier" drying out the electrochemical sensor, how long was the sensor exposed to this air? How old is the sensor?

Most CO sensor circuits I've seen have built in temperature and humidity compensation circuitry, so I would lean more towards a contaminated zero gas.

What is the composition of your zero gas? (i.e., pure N₂, or filtered "air")

Did the meter respond properly to "bump" / "span" gas (i.e., CO of a known concentration)?

What is the composition of your "bump" / "span" gas? (i.e., is the CO added to pure N₂, or to filtered "air" )

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Just my $0.02...

Most testers I have used calibrates the CO at its maximum safe limit (where the alarm will activate) with a calibrated gas source. It is then Zero calibrated with the ambient air. If this is done in a contaminated environment such as a smoke filled space, it will give false readings such as your -3ppm.

This will not change the Alarm level. It will only change the scale and accuracy of quantitative readings. Always ensure it is zero calibrated in fresh air.

Yes a room where people are smoking is contaminated by carbon monoxide. Carbon monoxide is cumulative in the lungs and will eventually starve your blood cells of oxygen. You will die

Carbon monoxide can also be produced with any incomplete burning, or inefficiently operating motor

Thanks - Techno and The Jman.

This happened years ago when we were at the bottom of the learning curve. We found that, at the ppm levels we are looking at, ambient air is too contaminated to be used as a zero reference. Those were the days when we first came across the anomaly - and as the meter was calibrated by the mftr we took the 'direct' meter readings at face value.

We now use the air from the purifier at the start of the test for a zero reference. At the top end, and numerous intermediate points, we calibrate with a known amount of (zero air) injected (by a micro-syringe) with a known amount of pure CO.

This gives us a calibration chart of ppm against the scale reading of absorbence at the wave number for CO. This technique is limited to bench testing during design and development - it is too long winded for production quality control - where we use simple direct reading meters calibrated to an accuracy good enough for the purpose.

However, the original concept of air with -3ppm of CO in it - still lingers in the mind.

Thanks for taking an interest.

Simple answer- it's all relative......to your reference.

I think someone like Einstein said that.

Then theoretically.... If you had a chemical environment of a limited chemical A that was reactive to CO, and chemical A could absorb 3 ppm CO, it would be possible.

Unfortunately, in this case you would have to test for chemical A to produce these numbers. I don't think your machine could do this.

techno,

You say "If you had a chemical environment of a limited chemical A that was reactive to CO, and chemical A could absorb 3 ppm CO, it would be possible."

But you can't react with or absorb something that ISN'T THERE.

So yes, you could theoretically go from a 3 PPM ambient CO concentration to a ZERO concentration in the presence of "chemical A", but you can't go from 1 PPM to -2 PPM, or have a "negative" gas concentration, at least not in reality.

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Just my $0.02...

If chemical A was "capable" of absorbing 3 ppm CO it is effectively -3ppm CO

"If chemical A was "capable" of absorbing 3 ppm CO it is effectively -3ppm CO"

NOT if there is less than 3 PPM of CO to absorb.

I would possibly say that "chemical A" is Potentially -3 PPM CO, not effectively

correct

You said " NOT if there is less than 3 PPM of CO to absorb"

If there is only 1 ppm to absorb -3 + 1= -2ppm

If there is 2ppm to absorb -3 + 2 =-1ppm

if there is 3ppm -3 + 3 = 0 ppm

if there is 4ppm -3 + 4 = 1 ppm

If Meter A measured the amount of chemical A and mathematically calculated the amount of CO it can absorb; output could be in form of "-ppm CO" once all chemical A is gone it would read 0ppm CO any more CO would change to the +ppm. I guess it would have to use a CO sensor for + CO

Oh well, Chemical A is only theoretical. No sense getting worked up over imaginary chemicals.

or is it?

• http://www.springerlink.com/content/r44784225285258l/
• or a room full of spider plants http://www.earthwitchery.com/pollution.html

Thanks again.

It is like the story of the empty cafe. Two people entered and had a meal. Three people left. Thus the next time someone goes in it will be empty.

A previous location measured total chlorides going out the door and the limit was in the ppm range. The FTIR analyzer measured a spectrum of chloride species and we used that to determine our total chloride content. Some of them read negative values most if not all of the time and I spent three solid hours arguing with my boss that we needed to normalize the negative values to zero since there couldn't be less than 0 ppm of anything and that a negative value in the sum would mask other chloride species increasing in concentration. Needless to say, we still sum the negative values into the total!

Don't you just hate when the "boss" who does not understand a process makes a stupid decision just because he would rather trust a machine then a person, or he has some other political agenda.

Quite so!

Doesn't -3ppm signify that the calibrating process was off by at least 3 ppm, and probably a little more, to account for the ambient concentration at the site, before starting the calibration?

Yes, I thought that has been clearly established.

Don't get caught up in all the banter.