infinityedge

Recipes 

Something along these lines:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&v ed=0CDwQFjAB&url=http%3A%2F%2Fwww.nt.ntnu.no%2Fuse rs%2Fskoge%2Fprost%2Fproceedings%2Fifac2008%2Fdata %2Fpapers%2F2543.pdf&ei=cI35UPrKOIXAigLZ9YGADg&usg =AFQjCNHthPZ0bfCP867eiHfEDfWtMCQ1fQ&bvm=bv.4124887 4,d.cGE

http://www.sciencedirect.com/science/article/pii/S0967066109002329

Basically, face a webcam at the sight glass then use OpenCV to determine where the edge is between liquid and air, then calculate the volume based off of the calibrated pixel location of the interface.

Seems like a fairly straight forward, no touch way to calculate volume with a fairly low cost if you are already using some sort of computer to automate things.

theonetrueruss

Recipes 

should be doable. There are probably a number of ways you could solve it with OpenCV.. line detection sounds like a good choice. I haven't played with the line detection but the other parts that I have used (mostly face detection) were pretty easy to work with. Great library. Good luck!

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TheOneTrueRuss
Fat Messiah Brewing

alien

Recipes 

A coloured float in the sight glass might help if you go this route.

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Magic Smoke brewhouse and grill

Automatic Smoker - Cooler MLT - Counterflow Chiller - Folding Brew Table

infinityedge

Recipes 

If one was willing to use a float, you could wrap IR reflective tape (or paint) around a cylindrical float and use a Wiimote to calculate the position change:

http://arstechnica.com/science/2010/12/scientists-wield-wiimote-to-measure-evaporation/

http://onlinelibrary.wiley.com/doi/10.1029/2010WR009350/abstract

Wiimotes are pretty easy to interface with. The camera outputs the position the top 4 brightest IR points at 1024x768 resolution. Provided the heat source doesn't overpower the sensor, it might be possible to get the sight glasses of three keggles in a single level arrangement covered by one wiimote.

That might be just as cheap and easier than the OpenCV route.... hmmm....