Nitrox/Oxygen Analyzers

[Meng_Tze]

.....
But does that really matter? Hummm, not really. What you're trying to do is to determine 'do I have air or Nitrox in my tank and what is the percentage of O2 (within 1%) (in the case of technical shops that might include determining if you have pure O2 and Trimix, also). The resolution tolerance of the readout on an analyzer is only 1.0% anyway which means it's only accurate to that 1 percent.

You are right there.

Most display readouts have a 2%-3% tolerance, then there is the tolerance of the actual cell; usually 1% at 1Bar. And if you have analogue components in the voltmeter circuit (an oxygen checker actually is just a volt meter and most still have analog components.... you end up with a huge error. The thing is the 'relative error' between two measuring points.

You calibrate at one point and call that something (say 20.9% O2), then you measure the gas to be dived. If the relative error between the points is less than a few % points, you are fine.

Measuring 34% when the actual gas is 32% is no issue. Measuring 36% when the gas is 50% is an issue......

 

[bullshark]

The O2EII is the best analyzer on the market. I have used one for about six years, analyzed hundreds of tanks. It works perfectly every time.

FYI the O2EII comes with a handy card that very accurately predicts O2 concentration at various temperature/humidity combinations in tabular form. Generally, if your on a boat in the tropics the answer is 20.5 or 20.6. To calibrate, just pop off the sampling dome and wave it around for a few seconds. Dial in the calibration value and you're done. Wave it around a little to make sure its set. This is especially important when new as all O2 sensors tend to be a little jumpy until they've had some exposure. Using this method I have never failed to get 20.9 when cross-checking with a tank of EAN21.

The sampling dome is what makes the O2EII so excellent. Due to a tiny inlet orifice and a large outlet, it is impossible to elevate the PO2 artificially which is what happens in virtually all the units that connect to a tank or inflator hose.

The air-tight sensor plug is also a special feature. It greatly extends sensor life.
Tip: When using the O2EII, place the dome against the valve, give it a quick shot (on/off) and then wait. The dome holds a significant amount of gas that will keep reacting with the sensor. Once it stops climbing, then give it a slow hiss, and when it stops climbing again you're done. Average time to test a single tank: less than 30 seconds for the first, then less than 10 for each additional tank. The dome is already full and the sensor is already "hot" so all you need is a few seconds of slow hiss to flush and re-fill.

BTW just about any O2 sensor will cost $100 to replace. This is chicken feed. Have you checked out what it costs to go diving?

safe diving,

bullshark