Richard Feynman Side Hustles
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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.
Serious question: Is Dr. Clark the guy who invented the modern soda can pulltab, too? Someone who lives in YS invented it, and made a kajillion dollars by solving the problem of dangerous, sharp-edged pulltabs littering ... everywhere.
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.
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.
That hits a bit close to home!
> 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.
What does "adds back an oxygen molecule" mean?
Elaborate and you'll find the issue with this setup.
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."
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.
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.
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.
Zinc can do this too. But I like silver, its oxide has decent conductivity.
One of the common arrangements on a basic two-electrode sensor is to have one gold electrode to make contact with the electrolyte, and the electrolyte provides conductivity to a sacrificial silver electrode. With electrolyte exposed to the atmosphere through an oxygen-permeable membrane.
As oxygen makes its way through the membrane, it is consumed by the silver at a steady rate and equilibrium is achieved relative to how much oxygen is in the atmosphere. This generates a steady current which is amplified to move a needle on a gauge, where there are knobs to adjust the meter until it displays the correct amount of oxygen during calibration against a known concentration. And must also be calibrated to display zero when there is no oxygen.
Eventually even if the membrane never gets fouled the oxidized silver builds up in the electrolyte chamber and response deteriorates so maintenance is needed. Remove the membrane, polish the silver, put in fresh electrolyte, new membrane, and re-calibrate.
Adding a third electrode opens up a number of further possibilities.
One of them is the option to use an additional inert gold or platinum contact or a salt bridge as electrical reference against the original gold or silver as the sensor. Plus using a more complex circuit than a plain amplifier, apply controlled responsive current to the sacrificial silver at the same time. So rather than directly amplifying the current produced by different concentrations of oxygen existing in the electrolyte (and waiting for it to equilibrate), instead with 3 (or 4) electrodes the ionic silver concentration in the electrolyte can be maintained electronically in a steady state, and as oxygen permeates, the current required to replace the consumed silver is designed to make a dfferent kind of meter move the needle the same way as above. In this way the oxygen concentration in the electrolyte varies to a much more limited extent compared to waiting for it to be depleted from a high amount to zero before the meter will bottom out.
This can be equivalent to constant-ion electrochemical titration.
Disclaimer: I always like to handle things like this like lives depended on it, because lives depended on it.
You do the best you can. If you can only make inaccurate sensors, make inaccurate sensors. If you can make accurate sensors, make accurate sensors. If they're much more expensive, make both. If your competitor has more accurate sensors, learn how they work.
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).
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.
(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 )
Ergo...
This kind of work has been my primary income for the last 4 years or so. Nowhere near on the same level as Feynman, but I know enough about enough other things that I get a lot of reputational referrals.
sometimes (i'd argue often, actually), you don't even need that. simply having an outside/fresh perspective and the fact that you aren't part of any of the existing groups/silos is valuable.
Having the ideas is easy. Persuading and organization to change is not.
Perhaps it’s a cultural difference between the middle of the 20th century and now.
You can be all over the ball park and people always get their money's worth :)
If you do it where the client can take it to the bank, they will often come back to see what happens with those kind of returns if they actually invest something substantial.