Comment by boxed
Comment by boxed 2 days ago
Because then it doesn't alter the side of the membrane where it does the reading (plus one minus one equals zero). That makes the measurement more accurate.
Comment by boxed 2 days ago
Because then it doesn't alter the side of the membrane where it does the reading (plus one minus one equals zero). That makes the measurement more accurate.
You're not really making things clearer.
What does "adds back an oxygen molecule" mean?
It means you do an electrochemical reaction that releases an oxygen molecule, like the original explanation said. It doesn't really matter what reaction it is, but it could for example be electrolysis, where you split 2x H2O into 2x H2 and 1x O2.
The point is this reaction is reversible. In one direction, you end up with fewer O2 molecules than you had before. In the other direction, you end up with more.
Yeah, how do you add the oxygen molecule, and how do you know when you have to do that?
Elaborate and you'll find the issue with this setup.
How do you add the molecule? Well, you're not just dealing with single-digit numbers of molecules. Have an oxygen tank with a flow meter for example, open the valve to release the required volume of oxygen. The ideal gas law tells you how many molecules you let out.
How do you know when you have to do it? The sensor tells you how many oxygen molecules you consumed, as a proportion of the current flowing. So just let oxygen flow into the tank at the same rate as you're consuming it. Which you know because the device literally measures how much oxygen it is consuming.
I think the real issue is that the explanation in the tweet is from a physics perspective rather than an engineering one, which means it reads like it was implemented with impossible magic.
>open the valve to release the required volume of oxygen
Mega LMAO. I can assure you this is not what's going on, at all. Also, if you release oxygen in gas form into the liquid you're going to run into a zillion other problems.
One of the golden premises of measuring things is to avoid altering what you're measuring, lol.
The issue here isn't the setup, it's with people understanding it.
Specifically, if you assume a partial pressure of Oxygen and of all other gases on the electrode-side of the diffusion membrane, then you'll only see a certain number of "ionization events" per time, and you're limited in how much electrical signal you get by how fast oxygen can diffuse across the membrane. This is likely driven by maintenance of a partial pressure within the membrane. However if you re-ionize the oxygen that you deionized, then the partial pressure is much closer to equilibrium, and therefore the partial pressures are only dependent on the amount of oxygen outside of the membrane instead of being dependent on both the ionization rate and the recovery rate through the membrane. It probably makes the calculation a lot faster and more closely dependent on the environmental presence of oxygen which is what you want.