Hello, I want to make/buy a sensor that can tell the concentration of water in alcohol, and/or water in xylene (benzene with two methyl groups).
Is this something that is already out there, for Arduino, or is there a way to build this that anyone can think of?
One way I thought to do this was to use a column of alcohol in a hot dog shaped glass "bubble" and place it in a hollow plastic tube, it will rise or fall as the concentration changed. I could use simple buttons at the top and bottom that the bubble would hit when critical concentrations are reached. This seems like it might work but it is quite messy and I would need to find buttons that could be fully submerged without being destroyed.
I also see a lot of reference to moisture detectors, but I doubt they would be able to tell the difference between alcohol and water.
You must look for the differences in the mix e.g. the specific (?) mass of water = 1.0 kg/liter. Alcohol is lower. So by measuring the weight of a given volume you can derive the ratio.
Another option might be to determine the optical breaking index, but I think that is far more difficult and maybe not within range.
Another option might be the electric conductivity, but that would only work when using pure water and pure alcohol. Not suitable for determine the % alcohol in beer or wine.
How would you normally test these? The moisture sensors that I've read about are typically for testing soil moisture, so not expected to be precise, and they rely on testing the conductivity of water in the soil. I had a bit of a google and found that in the alcohol case, that it's pretty much non-conductive, and while water will conduct I'd think at low concentrations you're not guaranteed a reliable response. Your method with testing specific gravity might be more the go, but again would it be sensitive enough to do what you want?
For the Xylene question, would water sit on the bottom rather than mixing, so you could use a test like the water alarms in fuel tanks - where a float that sinks in xylene but floats in water sits on the bottom until water lifts it and you sense the movement?
Weight is a good idea! I'm not sure if it will be accurate enough though, I want to be able to measure it in at least 1-5% increments. I'll get my hands on some 100% etoh and try this out.
The fuel tank water alarm is also a really good suggestion, kind of like my glass bubble idea but way better.
The other problem is finding parts that can be fully submerged in any liquid, let alone xylene.
I'll tinker around with this and if I find anything interesting I'll come back and post about it.