Twinnie:
Hang on Lefty, are you just saying that SG can be determined simply by having two pressure sensors take a differential reading from fixed points? Because that would be much more simple (though far less sexy) than my idea. I could even attach the sensors to rod or something, the way I could move them from one bin to another providing I used the same type.
That is one method used in the process control industry, so yes. However one usually uses a single differential pressure sensor instead of two psig single port pressure sensors as the measurement range is usually small and using two different sensors would bring in calibration variations into the differential measurement. Again this method only works if the liquid level is always higher then the higher pressure tap, and there is no stratification of the composite liquid being measured. Also your sensor must be rated for liquid service and many of the inexpensive pressure sensors are for air/inert gas service only, so check the datasheet carefully.
I could even attach the sensors to rod or something,
Immersing the complete sensor(s) assembly including lead wires leaving is rather unorthodox and probably fraught with problems? Pressure taps are usually drilled into the side of the the vessel being measured. Both sensor leads should route down below the lower pressure tap level such that any trapped vapour bubbles will migrate up and back into the process being measured.
Lefty