O2 + CO analyzer choices.

[cool_hardware52]

You can calibrate to pure O2, which is probably (hopefully!) on the boat, but of course this is not optimal because 100% is much farther from 32% than 21% is. Can you take a little pony of air?

Actually, calibrating to ambient air can have an error of almost one percent in high temperature and humidity air.
View attachment 221240

I have a 6 cuft bottle of air for calibration. All analyzers measure PPO2, not the fraction, and calibrating ambient air vs the same air flow and resulting PPO2 will induce some error. Slight maybe, but it's still best to calibrate and sample the unknown using the same process.

I started bring the 6 cuft bottle when it became apparent that nobody on private boat I most often dive off of needed to fill tires…..



Tobin

 

[WarrenZ]

As with most things in diving it is measure with a micrometer, mark in chalk, and cut with an axe. One percent high or low in nitrox is not a show stopper in most recreational diving.

If you are doing the types of diving where one percent error is going to be a problem then you would probally not only have the extra tank of air for calibration but be doing a two point calibration and have a second and possibly third analyzer to check tanks. My redneck calibration I posted earlier will not be as accurate due to humidity as a proper calibration but it is better than no calibration. As you can see in the second picture in the article (side by side test on a set of doubles) there was a slight difference in the two calibrated sensors of .2 percent due to the age of my sensor in my OMS peanut, the sensor is almost 1 year old now. So even with a calibration in accordance with the manufacturer's specs there will be some variation.

 

[Tbar]

You can calibrate to pure O2, which is probably (hopefully!) on the boat, but of course this is not optimal because 100% is much farther from 32% than 21% is.

Unlikely as the O2 does not have a Quick Release to connect, and I would not want to use any of the safety O2 for calibration. Also no O2 at home.

Can you take a little pony of air?
Actually, calibrating to ambient air can have an error of almost one percent in high temperature and humidity air.

As I said "know that using air from a tank is best for calibration on any O2 analyser" but this is not always practical and deviation is not material. (for the recreational diving I do)

I could buy a pony for calibration, but that is expensive and will also need maintenance, we are surrounded by air!

Maybe one of the inflatable mattress pumps may do the job Spinifex Battery Electric Air Pump Black | Anaconda

 

[DiveNav]

..... Being unable to calibrate without a tank of air or gas with known O2 percentage may not be workable.

Actually this is not completely accurate.
What we say in the quick guide is: "You should NOT perform an O2 calibration by just exposing cootwo to ambient air as the gas flow within the device might be insufficient and lead to incorrect results."
And the reason why we say this is because it could take quite some time (5 to 10 minutes) for the ambient air to stabilize inside cootwo as the flow rate is limited (but not zero) and, unfortunately, divers tend to be always in a rush and we are worried that they do not want to wait that long to calibrate cootwo on ambient air. (Note that if cootwo was already exposed to ambient air then it should be OK as there is no more waiting time).
To be more specific ..... one of the issue with existing analyzers is that by having the O2 sensor directly exposed to the outside environment could lead to sensor damages if you get one of those hard to control valves (you open it a tiny bit ... and there is no air ... you open a tiny tiny bit more .... and you get the whole 3440 psi rushing out ... OMG). To mitigate this, cootwo has an additional internal "wall" that further limits the flow rate. The effects of this wall are quite apparent when cootwo is exposed to ambient air (no delta pressure).

So, to summarize, if you want to calibrate cootwo using ambient air you could do it. But you need to:
- position cootwo horizontally and make sure that input and ouput are not obstructed
- if cootwo was in a sealed container or you had just measured a gas different than ambient air then you should wait 5 to 10 minutes before calibrating it.

Alberto (aka eDiver)

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[Anthony A.]

I just purchased an o2 + co analyzer (bw tech microclip) and was wondering how much flow (lpm) is released if using a first stage connected to the tank followed by the analyzer connected to the inflator hose?

Reason i ask is because calibrations on this unit are done using 0.5lpm, which is quite low. If I can forego buying a flow restrictor, that would be ideal. Would the inflator hose act as a flow restrictor as its low pressure and if so, how much?