Gas analyzers and partial pressure

[dray_gnv]

When I analyze nitrox after fills at my dive shop, I either screw an attachment into a valve with a hose running to the analyzer or hold the unit’s sensor close to the valve opening as I open it a bit. Either way, the pressure of gas hitting the sensor isn’t just 1ATA. Are these analyzers sophisticated enough to measure gas pressure along with O2 percentage? Otherwise how do they get an accurate reading?

 

[dray_gnv]

When I analyze nitrox after fills at my dive shop, I either screw an attachment into a valve with a hose running to the analyzer or hold the unit’s sensor close to the valve opening as I open it a bit. Either way, the pressure of gas hitting the sensor isn’t just 1ATA. Are these analyzers sophisticated enough to measure gas pressure along with O2 percentage? Otherwise how do they get an accurate reading?

Nvm. Partial pressure isn’t absolute percentage.

 

[tursiops]

What the extra pressure does is push N2 molecules through the analyzer's membrane along with the O2 molecules that are supposed to be the only ones going through the membrane. Both the O2 and the N2 molecules dissociate in the acid of the galvanic cell, and it gives too high a current, thus you think you have a higher O2 percentage than you really have. Flow limiters in the hose keep the pressure from being too high, and give the same pressure from the air tank you used to calibrate your analyzer as the pressure you get when you analyze a Nitrox tank. Use the flow limiter if you have one; don't just blow gas onto the galvanic cell.

 

[crofrog]

When I analyze nitrox after fills at my dive shop, I either screw an attachment into a valve with a hose running to the analyzer or hold the unit’s sensor close to the valve opening as I open it a bit. Either way, the pressure of gas hitting the sensor isn’t just 1ATA. Are these analyzers sophisticated enough to measure gas pressure along with O2 percentage? Otherwise how do they get an accurate reading?

Are you diving extremely hypoxic mixes?

If not 1% probably isn’t going to make a huge difference

 

[inquis]

Either way, the pressure of gas hitting the sensor isn’t just 1ATA

Calibration should have a comparable pressure/effect, so it's pretty well compensated. That said, a flow limiter makes for very consistent measurements.