continuous Trimix blending using 2 nitrox analyzers

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For blending the HE first and for making 10/70 the equation regarding the first o2 cell would be pO2 air x (1- %inert gas besides air (for example HE)) or 0.21 x (1-0.70) and that would give you a pO2 reading on the first cell of 6.3% o2. You would then inject o2 after that but before the second cell to bring the reading back up to 10% o2 and analyze the final mix.
 
The Ideal Gas Law is one, but not accurate enough at typical pressures. To do it more accurately is far more complicated than one equation, unfortunately. I suggest you check out the Gas Blender Toolkit.
The two-analyzer method is measuring at ambient pressure at the compressor inlet. You don't have to (and should not) adjust the percentages to account for compressibility. If you make 18/45 (or any other trimix) at the compressor inlet you will have 18/45 when you analyze the cylinder (your analyzer is also at ambient pressure).
 
Thanks for the correction. I didn't initially realize this was being mixed on the fly (before going in the cylinder).

I'm curious as to how much gas is typically wasted from such a blending approach. Presumably some valve is adjusted until the analyzer gives the correct percentage for each stage?
 

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