Re: Method for detecting Ethanol in solution?
- From: Gregg <nospam123gcrume@xxxxxxxxxxxxxxx>
- Date: Fri, 15 Jun 2007 10:34:21 GMT
aubrey wrote:
On Jun 13, 4:36 pm, Evan <crawling.ch...@xxxxxxxxx> wrote:Just an FYI.....
Hi all, coming from an electronics/engineering background so I
apologize if there's an easy answer to this, I haven't come across it
yet...
I'm interested in being able to sense/measure alcohol fermentations
in
a hobby situation, say home brewing or winemaking, where normally one
would have to open the vessel and take samples in order to see
specific gravity via floating hydrometer or hand held refractometer.
There are a number of problems involved, one being tha the solution
of
course is not just alcohol and water, there are many other chemicals
present, as well as sediment, yeast and other things that impinge
upon
clarity (Which I think would preclude the near-IR sensor that I saw
someone mention in this group's archives)
I have not seen any comercially available sensor that measures
ethanol
in solution directly; i was thinking perhaps capacitance or
resistance
could reliably be an indicator, but as I mentioned before there are
acids among other things present which I'm sure would render that
kind
of reading useless.
The only thing resembling a lead I have is using infrared to observe
the CO2 bubbles leaving the air-trap on top of the sealed vessel; if
I
could get a reasonable estimate of the volume per bubble I think I
could work backwards through fermentation chemical formulas to arrive
at the portion of alcohol being produced. Now i'm wondering if I
could find some sort of sensor that does ethanol vapor (e.g., a
breathalyzer type sensor) and expose it to the CO2 exhaust from the
fermentation and get a reliable reading there, then i would just have
to make some correlation between the reading in the vapor and what is
in the emitting solution.
Any thoughts would be greatly appreciated; I'm sure there's a good
way
to do this, just have to find it...
Would you be willing to develop a method not for yourself, but for the
whole hobby community, i.e., a product?
There was literature involving optical fibers run through turbid
solutions published back in the 70s. Even though the light is totally
reflected, the wave function extends out into the solution, and the
absorbance spectra was acquired, if I remember the articles after 20
years.
I do happen to have at hand some near IR spectra of a water and an
ethanol sample from specimens that were handy, i.e., perhaps
contaminated. These specimens show absorbance for water at 972 nm,
and ethanol at a couple of peaks, including 908 nm. I haven't checked
these values against literature.
I would try to find a couple of diodes that emit at those two
wavelengths, run them through a fiber in the solution, and monitor the
absorbance. There is plenty of mischief to keep you busy as an
engineer, e.g., modulating the signal (in old language and technique,
"chopping") to eliminate stray light and electronic DC drift. Finding
the right length of fiber to give good sensitivity.
Sounds like fun. Also, every town in Minnesota seems to be building a
corn to ethanol plant. May be a good project to know a lot about.
They make hand held Raman units that can read through glass or from a distance of 10's of feet.
I don't think those units are cheap........
Not as much fun as building something that works.
Gregg
.
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