O2 analyser is a must or not????

[Mark Vlahos]

Thank's to all of you!!!! Really help me to make my mind... I'll buy an O2 analyser!!!

Buy one, make one from a kit, or obtain the parts yourself and make one, it's all good.

Purchase of a complete analyzer is the easiest but costs the most.

Getting a kit and putting it together your self is next down the price ladder.

Getting all of the parts separately affords you the most options for specific features like a 10 wind pot instead of a 1 wind pot. This option will almost certainly cost the least for a basic model.

I built my own with a 1 wind pot and later changed to a 10 wind pot, what a huge difference in ease of use. I will never choose a 1 wind pot again.

Mark Vlahos

 

[E Rick]

Thank's for the links!

 

[Puffer Fish]

Not seen the kit before - thanks, also.

 

[SparticleBrane]

Just to stir the pot a little!

Personally I prefer to calibrate the O2 sensor with either 100% oxygen from a pure O2 bottle, or ambient air. This way I can be pretty sure of what I am calibrating it to.
I don't trust "air" tanks enough to calibrate my sensor to them, especially at a dive shop on a rental tank that they "only use for air"--mainly because of the fact that you don't know what's in them. There's a good bet, however, that what you're currently breathing in ambient air is probably ~20.9% O2.

Example:
Right now my Al80s each have ~1400psi of 32% in them. The next time I'm going to go diving I'm going to just top them off with air because I get free air and on these dives I have no use for 30-40% O2--air is just fine. However, I now don't know "exactly" what is in my tanks unless I analyze them (or do the math). Just as an estimate it will probably be somewhere in the 25% range.

This kind of thing occasionally happens at dive shops--accidentally putting nitrox in an "air only" tank or air in a nitrox tanks. What if this happened and then you calibrated to 20.9 on a tank that somehow had 25% in it? Whoops...


On another note, I can't say that I've ever come across "nitrox mixing" problems. The molecules mix themselves through diffusion almost instantaneously. If you KNOW that you mixed the tank according to the chart and it's reading something waaay off then there's probably something wrong with your O2 sensor or it was not calibrated properly (see above). For me--if I fill the tanks slow enough so that they don't get too heated and throw off the pressure reading by too much then I can be fairly confident with a fill that it's about right, before I analyze it, just by knowing how many psi of xyz gas I put in.

 

[paulithepin]

You can't pick up your tanks from the LDS i use until you analyze the tank! They just won't let you leave without doing it your self! I do trust that they have my interest in mind and proprerly care for their equipment, after all there are a number of LDS's that would love to have my business! BTW MBT Divers in Pensacola is my dive shop of choice!

 

[Charlie99]

I don't trust "air" tanks enough to calibrate my sensor to them, especially at a dive shop on a rental tank that they "only use for air"--mainly because of the fact that you don't know what's in them. There's a good bet, however, that what you're currently breathing in ambient air is probably ~20.9% O2.

Actually, on a hot, humid day, you are breathing more like 19.5% O2.
http://www.sandiasnorkel.com/classes/cla-f_u3.htm

Also, you will get an error caused by having no additional pressure when checking ambient air, but a small amount of additional pressure when checking the nitrox tank (that's why you are supposed to use the same flow rate for the nitrox as with your calibration tank). This error's sign is such that it will add to the error caused by humidity --- the nitrox gas will read higher FO2 than it really is.

Waving the sensor around in air is good for a crude, coarse check. Using a tank of air for calibration will give you a more accurate calibration (and you will know it is an air tank, because of your initial crude ambient air check).

 

[SparticleBrane]

I guess the message here is that if you want to be really really anal--
Buy a small tank, say a 13cf, have it filled with air, and never use it for scuba. If you own your own O2 analyzer then use ONLY that tank to calibrate the analyzer. This way you always know what's in the tank you're calibrating with.

 

[jiveturkey]

I think it's important that the point is made to the OP that as a rule of thumlb, it is safe to use your LDS's O2 analyzer. Having your own is convenient but if you can't trust your LDS to have something so basic as a working analyzer, you shouldn't be getting nitrox or air or regulators or training or advice or anything from them.

 

[RonFrank]

I think it's important that the point is made to the OP that as a rule of thumlb, it is safe to use your LDS's O2 analyzer.

IMO it's likely safer to use the LDS analyzer. I say ths for a couple reasons. First they are more ridgid about changing the sensor than I would likely be. Second, they have more than one. I can use two different analyzers if one is acting up. Third they have multiple air tanks sitting around to do calibration. If my tank does not analyze withing 1%, I generally recalibrate with a second tank of air, and see if I get the same reading. If the second reading is off, than I will ask to try another analyzer.

I guess the point I'd make is that having the luxury of multiple analyzers, and multiple tanks of air is something I would not have at home. Heck, if I'm not comfortable with the air I also have an option of bleeding a tank down, and refilling it so I KNOW that it has air only in it.

 

[LG Diver]

There's no "additional mixing" that takes place in the tank after the fill. It happens during the fill. If there were additional mixing, then you wouldn't be able to take the tank from the shop right after filling. It would be too dangerous if the mix were off. Nitrox mixing is supposed to result within 1% of the requested mix. Even 1% is too much though. I prefer less than .5%.

As for owning your own analyzer, when I first got Nitrox certified, I didn't own one, but I also didn't dive Nitrox very often. I now dive Nitrox almost exclusively and do own my own analyzer. I will also probably be building a 2nd one this summer. It's a nice thing to have when you're diving it all the time. Even though I do mark the mix, I like to verify right before the dive, especially my deco mixes. So basically, figure out how often you'll be diving Nitrox and decide whether it's worth it or not to buy the analyzer.

This happens to me every time I get a Nitrox tank from the LDS. They analyze the tank while it's hot as soon as they've mixed it, and put a sticker on it and rack it. I walk in and ask for xx% Nitrox. They go to the rack, pull something that's labeled as being in that range and I take it back to the analyser (the very same analyser they used when they filled it). The measurement I get is guaranteed to be off by at least 1% from their original measurement, and it's been off by as much as 3% on occasion.

The only explanation I can think of for why some people see this and others don't is that some LDS's use partial-pressure blending while other's use a membrane system. In a membrane system the mix would enter the tank at the specified blend and no mixing is required.

Edit- I'm guessing that filling tanks from banked Nitrox would also result in an accurate reading instantaneously, since the blend has mixed in the bank.