I want to measure liquid level in very small tubes - 5 mm diameter, 10 mm depth. The type of liquid can vary. I'm considering an ultrasonic approach. From what I've read, I need a bistatic transducer configuration to eliminate the dead zone. Would you know of any transducers that would work in this application?
Since you are working with liquid, a closed top transducer would be advised. Bi-static is indeed a good solution since the depth is small (10mm). Since the diameter is also small, a high frequency (200kHz - 1MHz) transducer is also recommended, since they have a varry narrow angle.
However, actually using 2 transducers for a 5mm area is sadly unpractical. A transducer alone is twice that diameter. So perhaps a mono-static option is also a solution.
The question is also where you will position your transducer, is the measurement through the air or from underneath the tube. You could research that which approach is better. If you put a transducer underneath the tube and measured the distance from the water to the air, that can also be used to measure the level.
Also, depending on the types of liquid, you could receive varying results. Water has a different density than let's say Gallium (in liquid form).
So the advice is as follows: Research existing solutions for ultrasonic level measurement in which a mono-static ultrasonic transducer is used. And check the solutions where the position of the ultrasonic transducer is underneath the tube/glass/tank etc.
-Side note: You can't just place it underneath, you need to glue it with a kind of silicon glue, so the ultrasonic vibrations can be transferred. Regular glue stiffens the setup, which dampens the vibrations.
