Molex Connectors

[LFMarm]

I am considering building a cell-checker pressure pot as well. Many thanks for sharing your experiences in this thread.

How do you account from the fact that the vessel initially has air and the fraction of O2 changes as you increase the pressure?
I did some quick calculations below to simulate going from 0 to 38 psi measured by the gauge by adding O2 to a vessel of 1.26 L of volume initially filled with air at an ambient pressure of 820 mbar. The fraction of O2 goes from 21% (air at the beginning) to 81% when reaching 38 psi by adding O2. The pO2 in the vessel is calculated based on absolute pressure and fraction of O2 in the vessel.

 

[LFMarm]

Did some more investigating and happy to share the findings.

Method 1 (most commonly used): linearity check in pure O2

1. Take a reading in air at ambient pressure (this is the point at the bottom-left of the chart, used to extrapolate the expected readings), pO2 ~ 0.17-.21 depending on altitude, temperature, humidity.
2. Flush the vessel completely with O2 at ambient pressure (exhaust valve open). pO2 ~ 0.8-1 depending on altitude
3. Start measuring mV as you increase the pressure in the vessel until you get to about pO2 = 2.0.

This gives a chart similar to the one below (data is randomly generated). You can get to pO2 = 2.0 with a vessel pressure of just 17 psi.

Method 2 (alternative): linearity check in enriched air

1. Take a reading in air at ambient pressure (this is the point at the bottom-left of the chart, used to extrapolate the expected readings), pO2 ~ 0.17-.21 depending on altitude, temperature, humidity.
2. Start filling the vessel with O2 without flushing (exhaust valve closed).
3. Measure mV as you increase the pressure in the vessel until you get to about pO2 = 2.0.

This gives a chart similar to the one below (data is randomly generated). As you can see there are more measurements around pO2=1.0 compared to the previous method. This second method requires getting to a higher final pressure of about 27 psi in order to reach pO2 = 2.0.

Once I build the vessel for testing, I will check which one of the 2 methods is easiest and gives the best results.