Analox analyzer

[GlennL]

So I have an analox nitrox analyzer. I have noticed that it is dead on when calibrated with an air cylinder. However, if I am toting around nitrox I really won't have an air cylinder. This created the necessity to adjust for humidity. I have a humidity gauge at home and I can use it at home for the calibration offset. My question is, how do I accurately calibrate for humidity when I am traveling/ on the dive boat? Do you have recommendations for an accurate humidity gauge I can throw in my dive bag?

 

[lermontov]

So I have an analox nitrox analyzer. I have noticed that it is dead on when calibrated with an air cylinder. However, if I am toting around nitrox I really won't have an air cylinder. This created the necessity to adjust for humidity. I have a humidity gauge at home and I can use it at home for the calibration offset. My question is, how do I accurately calibrate for humidity when I am traveling/ on the dive boat? Do you have recommendations for an accurate humidity gauge I can throw in my dive bag?

When the absolute humidity increases the percentage concentration of the other constituents including oxygen decreases. so the Nitrox may be slightly hotter if you calibrate the analyser in surrounding air, but at 80% humidity and 90F it its only 20.2% so put you EAN DC settings 1% higher *(if it reads 32% set it at 33%)

 

[tbone1004]

So I have an analox nitrox analyzer. I have noticed that it is dead on when calibrated with an air cylinder. However, if I am toting around nitrox I really won't have an air cylinder. This created the necessity to adjust for humidity. I have a humidity gauge at home and I can use it at home for the calibration offset. My question is, how do I accurately calibrate for humidity when I am traveling/ on the dive boat? Do you have recommendations for an accurate humidity gauge I can throw in my dive bag?

First off, great question and always good to see people thinking about stuff like this. That said, your answer is basically what @lermontov said. The deviation isn't that much, though I argue you should never calibrate from an air cylinder and instead calibrate to ambient. The reasoning for this is that you are almost never 100% sure what is actually inside of said cylinder. +1% isn't going to make a significant change in your decompression, so accuracy of +.5% is about all I care about on an analyzer

I do disagree with him though about setting the computer higher. In scuba we always need to round towards safety.
With nitrox that means rounding the MOD up, and the EAD down. In the case of the analyzer reading say 32.3%, you would base your MOD on 33%, in this case 107/127 for 1.4/1.6, and you would tell your computer that you are breathing 32% which lowers your NDL a bit, but it is rounding to safety.

Any humidity in the air assists this safety rounding for decompression by giving the appearance that you are breathing a less rich mix, so it isn't something that I would calibrate for

 

[lermontov]

. In the case of the analyzer reading say 32.3%, you would base your MOD on 33%, in this case 107/127 for 1.4/1.6, and you would tell your computer that you are breathing 32% which lowers your NDL a bit, but it is rounding to safety.

yes this would be better-this covers any discrepancy with NDL

 

[NAM001]

In most cases this is not a problem.
1. if you get a tank of 32 it will probably be 32 and change. you round up for MOD and down for NDL. anyway no problem
2. If yo have a humidity issue it will not raise the reading much no problem whether you are exact or not.
3. If you are using 32% and you are not going to MOD then there is no problem whether the reading is exact or not.

I have a small 6 cu ft tank of cal gas. I get the 32% tank and I check it with my checker. and I also check the cal gas with the shop checker. Cal gas should be 20.9 Or any value really. Just so you know what it is. It could be 36% just so you cal your checker at the test gas value.

Now the shop has checked you test gas and your tank. Now you check your test gas with your tester and then the tank of 32%. On site you now know what your test gas is and cal accordingly before testing your tank on site. There are those that are concerned about oxidation of the inside of the tank lowering the O2 content. I don't worry about it cause I refill the test tank a couple of times a year just to do a gas change.

 

[tbone1004]

In most cases this is not a problem.
1. if you get a tank of 32 it will probably be 32 and change. you round up for MOD and down for NDL. anyway no problem
2. If yo have a humidity issue it will not raise the reading much no problem whether you are exact or not.
3. If you are using 32% and you are not going to MOD then there is no problem whether the reading is exact or not.

I have a small 6 cu ft tank of cal gas. I get the 32% tank and I check it with my checker. and I also check the cal gas with the shop checker. Cal gas should be 20.9 Or any value really. Just so you know what it is. It could be 36% just so you cal your checker at the test gas value.

Now the shop has checked you test gas and your tank. Now you check your test gas with your tester and then the tank of 32%. On site you now know what your test gas is and cal accordingly before testing your tank on site. There are those that are concerned about oxidation of the inside of the tank lowering the O2 content. I don't worry about it cause I refill the test tank a couple of times a year just to do a gas change.

cal gas should ideally be O2 since that is going to be the most accurate gas that you'll have access to provided it comes from lOx if possible or supplied tanks from the gas suppliers. These have been vacuumed and filled, so you know they're going to be as accurate as possible. It also gives you an ideal of any voltage limits from the cell itself since you can do a two point calibration

 

[NAM001]

cal gas should ideally be O2 since that is going to be the most accurate gas that you'll have access to provided it comes from lOx if possible or supplied tanks from the gas suppliers. These have been vacuumed and filled, so you know they're going to be as accurate as possible. It also gives you an ideal of any voltage limits from the cell itself since you can do a two point calibration

Dont you think that positiion is a bit extreem when we are using ambient atamosphere as a cal gas ???

If i have a shop that bulk stores nitrox or is constant blending and their inline meter says 32.3, and i check the tank and it says 32.1 then a 6 cuft tank of the 32.3 is as good of a cal gas as anything. There is a point where high precision has no place. When yo take a tank of 32 to 80 ft there is no need to be exact on the O2 content. +/- 1 is good enough.

 

[tbone1004]

Dont you think that positiion is a bit extreem when we are using ambient atamosphere as a cal gas ???

If i have a shop that bulk stores nitrox or is constant blending and their inline meter says 32.3, and i check the tank and it says 32.1 then a 6 cuft tank of the 32.3 is as good of a cal gas as anything. There is a point where high precision has no place. When yo take a tank of 32 to 80 ft there is no need to be exact on the O2 content. +/- 1 is good enough.

quite possible, but if you're going for a cal gas, it may as well be one that you know dead nuts is spot on. Me personally? I will either do single calibration to air, or dual calibration to air+o2

 

[stuartv]

quite possible, but if you're going for a cal gas, it may as well be one that you know dead nuts is spot on. Me personally? I will either do single calibration to air, or dual calibration to air+o2

How do you do a dual calibration on an Analox? There is only one adjustment knob.

 

[tbone1004]

read up on cell linearity. Not sure if the analox will give you mV's, but if it does, you can do your own two point calibration based on the mV's