Chagrin:
Docedison:
You stated thhat there would be a "Dry Tube" and Lefty mentioned that Air will compress but a liquid won't... so your returned data is anyones guess.I would disagree with Lefty as well; using a dry tube as the OP describes will give a valid reading.
You are free to disagree, but that in itself doesn't make me or you wrong or right. I gave my reasons why it will not work and you just say it will regardless but state no technical reason or description of how it can be made to work, so there we are.
Not sure if I can come up with a good real world example but I'd start by pointing out the millions of homes in the world with private water wells that rely on a pressure tank half-filled with air and read the water pressure from the top of that column of air. Should the air bladder in that pressure tank burst and all air be lost from the tank it doesn't result in any change to the water pressure in the home. Well, the water pump starts cycling more frequently but that's another issue ...
The issue is he seems to want to be able to measure the water level of a vessel by sensing the head pressure of the water, not the vessel air pressure above the water level, and I assumed it would be a simple vessel only under atmospheric pressure. Those are two different measurements requiring different sensor protection and mounting methods. If it's a pressurized vessel that one wants to measure the liquid vessel then one needs to use a two port differential pressure sensor with the sensor mounted at or below the bottom of the vessel with the high pressure lead (which will be liquid packed) sensing the total vessel + liquid head pressure and the low pressure lead running to the top or above the vessel which will cancel out the vessel pressure resulting in just the pressure difference created by the head pressure of the liquid. This low side 'dry' lead is subject to condensation buildup resulting in liquid gradually filling up the dry leg and causing an error in the true level measurement. Measuring the vessel pressure above the water level can be done with a pressure sensor mounted higher then the vessel and of course the liquid level cannot reach the sensor, but this measurement in no way tells you the level of the liquid in the vessel.
There is a method to read liquid level above a vessels height using a 'dip tube' attached to a 'dry lead' mounted higher then the vessel. It's one of a very few methods of determining liquid level in underground buried vessels, but it requires an adjustable air pressure regulator to be able to force air bubbles into the 'dip tube' at the liquid levels highest possible level. What one is reading is the back pressure changes that result from the height of the liquid level in the vessel. It tends to not be a real accurate method but can be made to work. Texmate: Programmable Meter Controllers, Panel Meters, and Bargraphs
Lefty