Nitrox Analyzer

[ScubaBunga]

I looked at analyzers and ended up building my own-similar plans can be found online. Just a sensor, arduino, and a few other parts. Sensor was the most at around $60. I was able to add a few additional features like calibration from air or 100%O2, a lock when results stabilize, and display of MOD with ability to change PO2 between 1.3 to 1.6. Then 3d printed a sensor cap and tank adapter, as well as getting the LP inflator adapter. I looked at CO sensors too and have yet to find one with proper resolution under $300!

 

[CuriousRambler]

<snip>A 1ppm reading could be operator error, especially use the bag approach, but when you call the dive is a personal call. Many countries have lower maximums allowed, but 10 ppm is probably safe enough. Yes, I have seen readings over 5 & 10 ppm and I have turned boats.

Thanks for the info! I hope you didn't take my post as argumentative, I just genuinely don't have a clue here, and you've clearly dedicated some energy to educating yourself, so I'm curious about your experiences.

What's an "average" tank read? You say 1ppm could be operator error, so is it pretty normal for you to see 1-2ppm and not worry, unless you start seeing >5? If/when you do see contamination, is it pretty consistent from tank to tank, i.e. compressor/fill station issues that contaminated a batch of tanks, rather than one-sie two-sies that are no good?

I guess for that matter, what's your meter read if you set it on a table in your hotel room? I assume that'll vary depending on location?

Forgive my ignorance...what is bank, stick and blend?

Bank would be big tanks pre-filled with a 32% or whatever, just waiting to be dumped into scuba tanks.

Stick is a "kleenex" term for a mixing device where you essentially have a constant calculated flow of pure O2 dumped into the intake of your compressor to yield the correct EAN mixture as output.

Blend is when you take a low/empty scuba cylinder, dump in a calculated amount of pure O2 into the tank, then top off with compressed air to reach your target mix.

 

[DandyDon]

What's an "average" tank read? You say 1ppm could be operator error, so is it pretty normal for you to see 1-2ppm and not worry, unless you start seeing >5? If/when you do see contamination, is it pretty consistent from tank to tank, i.e. compressor/fill station issues that contaminated a batch of tanks, rather than one-sie two-sies that are no good?

Tanks should test at zero every time and it gets boring when you keep getting zeroes - until you get your first reading. If I get any digits, I start reviewing my handling, asking around if anyone else has a CO tester (or in my actual case, try one of my others I do currently carry three models on trips), etc. If I get any digits on two different units, I ask the operator to have a stern talk with his fill station. If I get 5-10ppm, I start thinking about declining the dive depending on depth possible. If I got an 80 ppm reading like grf88 mentioned, I'd be tempted to go talk with the fill station owner myself, then report here on SB. If an overheated or otherwise malfunctioning compressor will let that much in, what else could it be letting in?

And no, just because the first 6 tanks on a boat checks at zero is no assurance that the next tank won't hurt or kill someone. Too much can change too quickly in a compressor.

I guess for that matter, what's your meter read if you set it on a table in your hotel room? I assume that'll vary depending on location?

I seldom notice it over zero. Hotel rooms seldom have CO alarms tho, while all hotels have water heaters, etc.

Blend is when you take a low/empty scuba cylinder, dump in a calculated amount of pure O2 into the tank, then top off with compressed air to reach your target mix.

But let me leave the building before that. Pure oxygen is scary!

 

[CuriousRambler]

Thanks for your insights, @DandyDon ! I haven't had any experiences myself, so it definitely helps to understand what people are seeing/doing for real, as I consider buying my own meter.

 

[DandyDon]

There are others on SB who know more than I do, but they have their reasons for being less vocal.

 

[NTJB]

I maybe should have qualified my post with Most O2 units require calibration before each use. Units like the OxySpy will let you know if calibration is required and can hold calibration for a period of time.

Gotcha, thank you. I will probably go with the Oxycheq Expedition units.

Tanks should test at zero every time and it gets boring when you keep getting zeroes - until you get your first reading. If I get any digits, I start reviewing my handling, asking around if anyone else has a CO tester (or in my actual case, try one of my others I do currently carry three models on trips), etc. If I get any digits on two different units, I ask the operator to have a stern talk with his fill station. If I get 5-10ppm, I start thinking about declining the dive depending on depth possible. If I got an 80 ppm reading like grf88 mentioned, I'd be tempted to go talk with the fill station owner myself, then report here on SB. If an overheated or otherwise malfunctioning compressor will let that much in, what else could it be letting in?

And no, just because the first 6 tanks on a boat checks at zero is no assurance that the next tank won't hurt or kill someone. Too much can change too quickly in a compressor.



I seldom notice it over zero. Hotel rooms seldom have CO alarms tho, while all hotels have water heaters, etc.


But let me leave the building before that. Pure oxygen is scary!

Very helpful! So you are saying that, if you get anything other than a 0, you would not dive that tank? I'm just trying to figure out if there's any "acceptable" amount of CO in a tank...

 

[DandyDon]

So you are saying that, if you get anything other than a 0, you would not dive that tank?

No, but if you get the Oxycheq CO and get any digits, you'll have reason to question your own handling of the unit vs the quality of the air. I take more risks in life than I would suggest anyone else, but I'd dive a tank with 5 ppm from that unit. I'd dive 10 ppm on a shallow dive. But I would have a discussion with the operator.

If I get any digits, I start reviewing my handling, asking around if anyone else has a CO tester (or in my actual case, try one of my others I do currently carry three models on trips), etc. If I get any digits on two different units, I ask the operator to have a stern talk with his fill station. If I get 5-10ppm, I start thinking about declining the dive depending on depth possible. If I got an 80 ppm reading like grf88 mentioned, I'd be tempted to go talk with the fill station owner myself, then report here on SB.

 

[ScubaBunga]

Has anyone built their own CO analyzer? I’ve found some SPEC sensors that seem to have the proper range.

 

[W W Meixner]

This is what I currently use. Small rugged and come with an adapter to use off the BC inflator hose if your rig is already setup. Because we sometimes just top up tanks in the field it comes in handy. Also use it to check tanks when I am shore diving in the islands. Yes most shops have them but I just like to double check as it never hurts. As far as I know, CooTwo is no longer in business and they made a pretty good O2/CO analyzer. @DandyDon seems to be the go to CO guy.

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BF...

Me too...I wouldn't leave home without mine...

I'm a Tobermory regular from July through Sept...busy weekend mornings...there may be as many as 50 divers in the shop in queue waiting to use the shop analyzer...of which there is only one...

Having my own analyzer is a much better option...for $250...and sensor life in the 48 mo range...from my perspective it's a sound investment...

As well...with the rebreather...I'm checking mix as part of assembly checklist procedures...which is either at home...or at the hotel...

DGX maintains stock of both the AII Palm...and replacement sensors...

W.M...

 

[stuartv]

The Analox O2 analyzer is the one I have seen the most of (by far) out in the field.

I got my own Analox after a trip to Hawaii where the shop I booked through met me at the dive boat with my tanks of Nitrox. The DM that brought the tanks did not have an analyzer with him. The boat did not have an analyzer. I had to choose between diving unanalyzed tanks that were allegedly Nitrox 32, or diving other tanks that were air. I used the tanks of air. And bought my own analyzer as soon as I got home.

Sometimes, dive charter logistics mean that you don't have any opportunity to analyze your tanks until you are on the boat and have already left the dock. Analyzing your tanks is too important (to me, anyway) to RELY on the boat having a working analyzer that is in good shape. That is why my Analox is in a small, waterproof Pelican case that I can have in my dive bag when I get on the boat. When I analyze, I will use my own. If I get questionable readings or mine is dead, then I will hope the boat has one and use that. If mine was dead and the boat didn't have one that worked, I honestly don't know what I would do (besides be royally pissed).

My Analox was a shop demo model and I don't know for how long. I keep it in a small Pelican box, and with the "sensor saver" cap in it. I periodically checked calibration against pure O2, to confirm the sensor was still good and it lasted me almost 4 years. And I have no idea how old it really was when I bought it. So, it analyzed tanks for me over probably 200 - 250 dives. The replacement was a bit over $100, if I recall correctly.

I have never tested for CO. I know I should. I just have not yet gotten off my wallet and bought an analyzer for that.

But, from what I have read, the amount of CO that will hurt you is somewhat dependent on the depth you dive to and, therefore, the actual amount of CO in your lungs. At 100' there will be twice as many CO molecules in your lungs as there were when you were at 33'. Hopefully, it's just 2 times zero.

My gut is that 3 ppm is fine for any kind of normal depth (even to 200'). Over 10 and I wouldn't dive it (which begs the question of why I have not bought an analyzer yet!). Over 5 and I would only be likely to use it if the dive were going to be pretty shallow.

One thing that I *think* about the Palm O2 analyzer is that it can only be calibrated to air. I could be wrong about that. If so, somebody please correct me.

If that IS correct then that means a couple of things:

The correct calibration for atmospheric air is frequently not 20.9. Depending on barometric pressure, ambient temperature, and ambient humidity, it can be as low as maybe 20.1 (I don't have my calibration chart in front of me). For me and where I live, it's often 20.5. So, the only way to really be sure of the Palm calibration is to calibrate it using a scuba tank that is KNOWN to be air. That will (should) be perfectly dry (i.e. no humidity) air and can be used to calibrate to 20.9.

In contrast, the Analox comes with a chart so you can see what the correct value is and then calibrate to that. And, if you are going to be analyzing tanks with high O2 content (above 50%), you can calibrate the Analox to 100% using a tank that is KNOWN to be pure O2. That will then give you a (likely) more accurate reading on this high O2 gases.

How much does all of that matter for normal recreational diving (i.e. Nitrox that is 40% O2 or less)? Probably not really a whole lot. The Palm calibration might be off by 1/2 a percent or so. Given how "rough" NDL calculations are anyway, having your computer set for a mix that is 1% off from the "correct" setting is not likely to kill anyone (unless they were going to die with a correct Nitrox setting anyway) or get anyone bent.