Recommendation for a scuba oxygen analyzer

[Scared Silly]

I have had really good luck with the Analox EII02. Get the sensor saver cap and you will find the sensors will last 4 years or more. Sensors are consumable and "wear" out regardless. Their price has seemed to come down recently. BTW even if shops have their own analyzer it is worth having your own - especially at dive resorts when 6 other people all want to analyze their cylinders and there is only one to be had. I also have a pressure checker and a CO detector.

 

[jgl51]

I just purchased a Palm O2 analyzer. Oh big surprise when reading the manual (should have read it before purchasing...):

For measurement of O2 >30% (basically all Nitrox diving) NEVER use air for calibration (but 100% O2) !!

(The problem I never have access to 100% O2 when diving....)

Now I have used several analyzers up to now for Nitrox diving and always used ambient air for calibration.

Can someone explain why not use air for O2 measurements above 30%? What happens if I do (significant, life threatening error)?

I wrote the manufacturer but still await a reply !!

 

[Oldbear]

This topic comes up about every 6 months...I myself started a thread asking the same thing about 3 or 4 years ago. I was recommended the Analox O2II and I bought one. At that time I had to buy my own case, now they come with a Pelican case for a few extra $$$...well worth the extra change.

I still have my original analyzer and use it frequently...and the best part is mine analyses O2 in both Imperial and Metric so I can use it worldwide.

 

[jgl51]

This topic comes up about every 6 months...I myself started a thread asking the same thing about 3 or 4 years ago. I was recommended the Analox O2II and I bought one. At that time I had to buy my own case, now they come with a Pelican case for a few extra $$$...well worth the extra change.

I still have my original analyzer and use it frequently...and the best part is mine analyses O2 in both Imperial and Metric so I can use it worldwide.

Do you also need to use 100% O2 for calibration for measurements of O2>30%??

 

[tursiops]

I still have my original analyzer and use it frequently...and the best part is mine analyses O2 in both Imperial and Metric so I can use it worldwide.

?? I hope you are joking......

---------- Post added March 29th, 2015 at 11:00 AM ----------

OD

I just purchased a Palm O2 analyzer. Oh big surprise when reading the manual (should have read it before purchasing...):

For measurement of O2 >30% (basically all Nitrox diving) NEVER use air for calibration (but 100% O2) !!

(The problem I never have access to 100% O2 when diving....)

Now I have used several analyzers up to now for Nitrox diving and always used ambient air for calibration.

Can someone explain why not use air for O2 measurements above 30%? What happens if I do (significant, life threatening error)?

I wrote the manufacturer but still await a reply !!

The reason to use 100% O2 for calibration is for gases with a high percentage of O2...you want to calibrate against a known gas closest to your unknown gas. Air is much closer to recreational Nitrox (<40%) than is 100% O2.....so use air.

But beware that you do not necessarily set the analyzer to 20.9 when calibrating to air; the correct percentage depends on the temperature and especially the humidity of the air. You may need to set the analyzer to 20.7 or 20.6, for example. I believe the unit you have automatically assumes 20.9, so you have two options: (1) use a tank full of air as your calibration source (low humidity, probably low temp), or (2) subtract 0.2 or 0.3 from your unknown-gas reading after you've measured it.

People will say, don't worry about 0.2 or 0.3.....but what happens if you calibrate to room air (with the auto 20.9 calibration) then measure 32.6 with your unknown gas? Do you set your computer to 33%? Actually, the unknown gas may actually be 32.3 or 32.4....so rounding down to 32% makes more sense. People will say that 32% and 33% are the same, not to worry, they are within 1%. But, not really; they have different MODs and NDLs, for example.

If in doubt, for recreational diving, many folks always round DOWN (on their computer) to a lesser percentage O2, so they are tracking their N2 exposure conservatively, but round UP (in their head) to the higher percentage for the MOD they plan to use. So, in the example, you auto-calibrate (assuming 20.9) to room air, measure something between 32% and 33%, then set your computer to 32% and use the MOD for 33% for your dive, i.e. 107 ft. In truth, I would just hold my dive to 100 ft to add some additional MOD conservatism too, but would know that I've got another 10 feet or so if I need it without breaking any PPO2=1.4 limits.

For technical diving, it is a different game....higher O2 percentages, thus the need to seriously track O2 and PPO2 levels....and more care is likely required.

 

[jgl51]

?? I hope you are joking......

---------- Post added March 29th, 2015 at 11:00 AM ----------

OD

The reason to use 100% O2 for calibration is for gases with a high percentage of O2...you want to calibrate against a known gas closest to your unknown gas. Air is much closer to recreational Nitrox (<40%) than is 100% O2.....so use air.

But beware that you do not necessarily set the analyzer to 20.9 when calibrating to air; the correct percentage depends on the temperature and especially the humidity of the air. You may need to set the analyzer to 20.7 or 20.6, for example. I believe the unit you have automatically assumes 20.9, so you have two options: (1) use a tank full of air as your calibration source (low humidity, probably low temp), or (2) subtract 0.2 or 0.3 from your unknown-gas reading after you've measured it.

People will say, don't worry about 0.2 or 0.3.....but what happens if you calibrate to room air (with the auto 20.9 calibration) then measure 32.6 with your unknown gas? Do you set your computer to 33%? Actually, the unknown gas may actually be 32.3 or 32.4....so rounding down to 32% makes more sense. People will say that 32% and 33% are the same, not to worry, they are within 1%. But, not really; they have different MODs and NDLs, for example.

If in doubt, for recreational diving, many folks always round DOWN (on their computer) to a lesser percentage O2, so they are tracking their N2 exposure conservatively, but round UP (in their head) to the higher percentage for the MOD they plan to use. So, in the example, you auto-calibrate (assuming 20.9) to room air, measure something between 32% and 33%, then set your computer to 32% and use the MOD for 33% for your dive, i.e. 107 ft. In truth, I would just hold my dive to 100 ft to add some additional MOD conservatism too, but would know that I've got another 10 feet or so if I need it without breaking any PPO2=1.4 limits.

For technical diving, it is a different game....higher O2 percentages, thus the need to seriously track O2 and PPO2 levels....and more care is likely required.

Thanks for the detailed and interesting reply to my question.

The "Nitrox" mix is used mostly either to extend the dive and / or during deco stops.

I have read about the influence of temperature, pressure (altitude) and humidity on the reading. Pragmatically we perform these analysis outdoor in various conditions. In addition the calibrating gas is under pressure. Therefore based on your discussion one need to "reduce" MOD as we will never be able to correct accurately for all these parameters??

You are correct regarding the palm there is no adjustment of whatever measurement is made (calibration or gas analysis).

Thanks again.

 

[M-diver]

I have Palm O2 analyzer and I noticed the directions for calibration in the user manual. I do have both air and O2 usually so not much of an issue but I also checked calibrating on either air or O2 and then measuring mixes 28% to 50% and I can tell that the difference is negligible regardless what I calibrated with. Analytical Instruments make pretty good products, I don't think you will go wrong with the Palm.


Sent from my iPad using Tapatalk

 

[PfcAJ]

People will say, don't worry about 0.2 or 0.3.....but what happens if you calibrate to room air (with the auto 20.9 calibration) then measure 32.6 with your unknown gas? Do you set your computer to 33%? Actually, the unknown gas may actually be 32.3 or 32.4....so rounding down to 32% makes more sense. People will say that 32% and 33% are the same, not to worry, they are within 1%. But, not really; they have different MODs and NDLs, for example.

1% doesn't matter at all. None of this scuba stuff is that precise since physiology is involved.

 

[geoff w]

Analox FTW! I've been in lots of dive shops with nitrox and boats / resorts that supply nitrox, and finally broke down last year and bought my own personal analyzer. Last year in Palau the boat's analyzer wasn't working right so they used mine. The sensor saver cap is great for extending the sensor, but it needs to acclimate to ambient air for a few hours before producing reliable / repeatable readings

 

[jgl51]

I have Palm O2 analyzer and I noticed the directions for calibration in the user manual. I do have both air and O2 usually so not much of an issue but I also checked calibrating on either air or O2 and then measuring mixes 28% to 50% and I can tell that the difference is negligible regardless what I calibrated with. Analytical Instruments make pretty good products, I don't think you will go wrong with the Palm.


Sent from my iPad using Tapatalk

Interesting feedback.

Probably the Palm O2 manual was written by lawyers...

I must say that until now I have never seen divers either at the fill station or on boats calbrate their analyzers with O2. (sometime they do not even calibrate... an other topic!!).

---------- Post added March 30th, 2015 at 09:43 AM ----------

Analox FTW! I've been in lots of dive shops with nitrox and boats / resorts that supply nitrox, and finally broke down last year and bought my own personal analyzer. Last year in Palau the boat's analyzer wasn't working right so they used mine. The sensor saver cap is great for extending the sensor, but it needs to acclimate to ambient air for a few hours before producing reliable / repeatable readings

Palm O2 manual says 15' to 20'. Few hour sseems very long. May want to check if sensor not at end of its life.