Nitrox lessons $150 bucks--Why?

[VTernovski]

Here is a good article on EAN analysis:

http://www.sportdiverhq.com/analysis.htm

 

[padiscubapro]

VTernovski once bubbled...
Well, one other important thing when analyzing, and which is often omitted or disregarded (also depends on an analyzer) is the flow rate. It should have a specific flow rate, and more 'high end" analyzers will have the flow meter, where some cheaper hand held ones do not. Also, when you calibrate, it is important to know the humidity factor, which determines the starting point of your calibration, it is usually best to first calibrate the unit on a regular air tank that you know has super dry air in it. I usually set it to 20.9, but I know that option is not always available. In the very humid environments (Caribbean) the starting point will be less than that; I think it’s more like 20.6 or so. Please correct me if I am wrong.

The most accurate way to calibrate an alayser is to calibrate it using what you are going to sample with..
calibrate it using a reg with a controlled flow rate on a cylinder containing oxygen compatible air.. set it for 20.9 it doesnt matter where you are the gas from a scuba tank is dry... dont calibrate from ambient air, especially indoors where the oxygen content can be below "normal" content for your altitude..
for example the "normal" pressor for someone at 2000ft altitude is 977 mb, this means, if the meter was calibrated at sea level and brought to altitude it would only read 20.4 for air, while 100% would read 97.7 % This also shows why its important to calibrate where you are going to analyze.. more detail below

now use the same reg and flow rate to check your gas...


oxygen sensors measure PO2 not percentage.. so if there is gas flowing pressure is above ambient... if you use a controlled flow pressure becomes irrelavent, since its "zerod" to a know standard..


lets take a simple example.. standard sea level is defined as 1013 mb, in the carribean normal readings are around 102omb while up in the high northern lattitudes are 1000mb

so 1000mb X 20.9% - .209, 1020mb * 20.9% = .213 as you can see small pressure changes do make a difference, if you zero it to read 20.9 at ambient air, once you start flowing gas you are asserting some increased pressure, how much depends on the flowrate and how restricted the output orafice is..

oxygen sensors are most accurate around calibration point and are "generally" linear, but the error does increase the farther you get away from the calibration point..

small errors near the calibration point extend to larger errors at farther ends.. the calibration sets the slope of the line..
what this means in plain english (the numbers are made up for illustration), say the slope was supposed to be .02, but your calibration made it .01, 20 points away should be a .4, but you would only be reading a .2, 40 points away you should be reading a .8 but you are showing only a .4, so you can see how the error gets amplified...
how does this effect me... well if you calibrated with air, the error at 32% isn't that big, but by 100% it could be several percent off...

 

[Cudabait]

You've already got the compurters. If it isn't a matter of the money, take the course. It's within reason. Obtain the necessary tables in addition to the computers. If you then intend to rent nitrox, your current equipment should suffice up to 40 per cent oxygen. Enjoy.