You'll find a lot of commercial sensors under the keywords "non-invasive ultrasonic level measurement" respectively "non-invasive ultrasonic level switch"
This is great stuff. I'm going to put together something which uses these principles. Why didn't i think of this method of fluid level measurement before ?
thanks chief
I didn't see this link before, I looked there and I think this is what I really need,
but in this link it states that I should get sonometer 30 system and I can't use only ultrasonic sensor.
I don't need sonometer 30 controller, i want those data in my controller, do you think it is feasible ?
I didn't post the link, but it's one of the very first google hits for "non-invasive ultrasonic level measurement".
I just wanted to show that this kind of measurements is feasible and utilized in industrial instrumentation.
You can either buy commercial instruments or design it on your own. I don't know your electronics and physics and mechanical engineering skills and can't estimate your chances to manage the design.