The present model of UVP has been developed for flow in such liquids as:
Some combinations of wall material and liquid are well suited, some not so well suited. The decisive factor is 'acoustic impedance' of wall and liquid (acoustic impedance is product of density and sound velocity of material). If acoustic impedance of wall material and liquid are at least similar, through-the-wall measurement is usually possible without significant problems.
In principle wall acoustic impedance should not be more than twice to three times test liquid impedance.
Generally, the ultrasound is reflected at the interface where acoustic impedance (density x sound speed) changes discontinuously. And thus, when the transducer is set outside the container wall for non-invasive measurement, a combination of liquid and wall is limited as follows:
The following combinations need careful consideration:
The easiest method is the following: fill a beer bottle with test liquid. Then sink transducer into the liquid and pull it out repeatedly. If measurement is acoustically possible, on UVP Monitor screen you will see profile movement corresponding to the transducer movement.
Yes. For example in colagen measurement is impossible. Thanks to its fibrous structure colagen features very high absorption of ultrasound so no echoes return back to transducer. There exist more media like this. Ultrasound measurement in very high absorption media is impossible, in plastic as well.
It is not practical to transmit ultrasound through a cast iron wall (which acoustic impedance is about 30 times the one of water) into water, since the interface would largely reflect incident pulses.
In most cases it is preferable to drill a small 8 mm diameter port into the pipe (4 MHz transducer with 5 mm active diameter) and insert transducer into a pipe flush with its inner surface. The transducer can be sealed with an O-ring. This removes all problems with wall impedance.