How did MOXIE "know" that it produced 5.4 grams of oxygen? Did it measure pressure rise in a container or just vent it? Did it use an oxygen sensor?

Question

CNN's Perseverance rover just made oxygen on Mars is great and welcome news! While Ingenuity has been achieving one "first" on Mars Perseverance was quietly achieving yet another.

After warming up for about two hours, MOXIE produced 5.4 grams of oxygen. This is enough to sustain an astronaut for about 10 minutes.

Question: How did MOXIE "know" that it produced 5.4 grams of oxygen? Did it pressurize an oxygen gas container and measure the pressure rise? or just let the gas escape into the atmosphere? Did it use an oxygen sensor to verify oxygen?

related and currently unanswered:

The (NASA Insight) team installed MOXIE into the chassis of the Perseverance rover in March 2019.

score 3 · Accepted Answer · answered Apr 23 '21 at 01:41

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Here is a simplified flow diagram of MOXIE

Oxygen production is calculated using the pressure, temperature, and flow sensors in the O2 output leg.

The product gases are exhausted to the Martian atmosphere.

References:

System Modeling, Design, and Control of the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) and Implications for Atmospheric ISRU Processing Plants
Mars Oxygen ISRU Experiment (MOXIE)

answered Apr 23 '21 at 01:41

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I see. From the first reference "...the outlet pressure of the MOXIE gas collection system is constrained by Viscous Flow Control Devices (VFCDs)... effectively temperature-compensated precision apertures... On Mars, MOXIE will electrolyze CO2 at a pressure between 400 and 760 Torr So they maintain a substantial pressure, but keep pumping atmosphere in and letting gas out, monitor the oxygen concentration, and integrate the product of O2 partial pressure times flow rate somehow. – uhoh Apr 23 '21 at 01:52
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I've just asked Is MOXIE's oxygen ready to breathe or is there CO2 and/or CO that would need to be scrubbed? – uhoh Apr 23 '21 at 23:06

How did MOXIE "know" that it produced 5.4 grams of oxygen? Did it measure pressure rise in a container or just vent it? Did it use an oxygen sensor?

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