Feynman's sensor, by contrast, directly measured the concentration of oxygen in the sensor, which gives the same result every time once the sensor is at equilibrium with the environment.
Just think of a thermometer.
If it removes heat as it measures it (consumes oxygen) then it will measure everything too cold if the system can't replace the heat that's removed (this is like having an insulated thermometer).
If your thermometer replaces heat as it removes it it solves this issue.
When is this an issue for a thermometer? If your thermometer is too large in terms of heat capacity for the objects you're measuring the temperature of.
That hits a bit close to home!
The dissolved oxygen sensor (the Clark electrode) was invented by Dr. Lee Clark at Antioch University (Yellow Springs, OH) and commercialized by YSI in the 1960s. A friend of mine worked at YSI from the late 60s thru the 80s on biosensors (glucose and lactic acid, using the Clark electrode as the basis) and worked directly with Dr. Clark.
Carl Feynman was born in 1962, according to what I'm reading, so if he was 14 that would have put this story in the time period early in the commercialization of these sensors.
Some good background:
https://derangedphysiology.com/main/cicm-primary-exam/respir...
https://www.anaestheasier.com/the-clark-electrode/
I'll have to hit my friend up to see if he knows anything about this. I'm certain he'd get a kick out of reading this, if nothing else.
> Do you have a similar speaking cadence as your dad? I can almost hear this in his voice.
I experience the same. Wonder if Carl asked chatGPT to write it in Richard Feynman style? :/
I troll; Regardless, it made me happy to hear Richard in Carl.
Some people around here really do think that way about Elon Musk.
They don't have any deep ideological commitment or overt cruelty, they just don't care enough. They justify themselves with claims such as "it's the way things are," "not my role," "everyone does it", or that it doesn't really make a difference.
But if everyone on X that doesn't explicitly support fascism and Nazism stopped using it, it would make an immediate difference. X would turn into something more like Truth Social.
By adding a third electrode to replace the oxygen every time one is smashed, you maintain a perfect balance and eliminate that suction. Because the room stays full, the sensor no longer relies on the speed of the oxygen rushing in; it simply measures the steady state of the oxygen already there. Even if gunk gets on the window, the sensor won't be starved of a reading. It might take a few extra seconds for the levels to settle, but the final number will be 100% accurate because the sensor is no longer emptying its own room to get a count.
The big gain comes from a change in how you interpret the presence of electrons.
The older approach converted oxygen to electrical current, the magnitude of current flow relating to magnitude of oxygen depletion. The assumption built into that approach is that low oxygen depletion levels meant low oxygen levels, but that wasn't the only potential cause, because it ignored variation in the permiability of the membrane.
The newer approach equates current flow to oxygen concentration, as the system doesn't deplete the concentration any longer. The permiability of the membrane in this setup only contributes to a longer initial delay as the inner chamber comes to equilibrium with the surrounding concentration.
By keeping the state of oxygen inside the probe constant and replacing consumed molecules you now can measure almost instantly.
Edit: I think I get it now, it's a chemical reaction. By applying a voltage with some polarity to the 3rd electrode you can run the reaction in reverse. Still very hard to achieve because you have to make sure the reactions happen at the same rate with the same efficiency, which is far from trivial. This must be a very high end sensor for all this effort to make sense.
The sensors must be consumable with a certain lifetime.
What does "adds back an oxygen molecule" mean?
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.
Elaborate and you'll find the issue with this setup.
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.
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.
1: as in, one with detailed knowledge in some specialized field (as of science or literature)
Mainly I take issue with the person I replied to implying "I don't understand the solution, therefore there must be some functional issue with the solution."
(A quick google brings up this document which describes the principle. No idea if this is the company in the story: https://semeatech.com/uploads/Tech_Docs/AN%20161205.pdf )
At least that's what I assume.
Before, you measured diffusion rate of oxygen and inferred oxygen concentration from that (the concentration outside the chamber is always greater than the concentration inside). Dirty membranes etc all changed the rate of diffusion, which caused issues.
After you measure oxygen concentration directly (the concentration inside and outside the chamber are always the same).