Level sensing
Hi guys,
In my game - Hydrocarbon Applications, level sensing is pretty important.
Depending on how stable the density of your fluid is, pressure is an easy way to do it - however, if you have pressure in your head space it will blow the level measurement out. Sounds like if the fluid is at 95C then it will be under pressure. Pressure still works, but you need a differential pressure sensor, or measure both pressures.
Then, if your fluid becomes more dense due to less alcohol, then your level sensor will tell you that you have more fluid than you have.
It seems your tube is clear, i.e glass or plastic. My suggestion is to use a capacitive level sensor. There is probably a capacitive level sensot in the fuel tank of your car, and you don't know about it.
Basically two parallel "probes" go from top to bottom in the fluid. There is a capacitance between the two probes, and this capacitance changes with the fluid level. Commercial versions that go in fuel and oil tanks cost thousands of dollars.
You could make the two probes from two parallel wires attached to tour tube. You can make a circuit with op amps that converts capacitace to voltage for input to the picaxe. Or, you can let soemone else do all the brainwork. You can buy a chip that converts capacitance to I2C, which you can read from a Picaxe 18X or 28X. You can get the breakout borad from Sparkfun
http://www.sparkfun.com/commerce/product_info.php?products_id=7918
If you don't want actual level, just that it gets to a level, you can use this sensor with the circular probe it comes with, attached at the strategic point to the side of your plastic tube.