TEST MEDIUM, THROUGH-THE-WALL MEASUREMENT

In what kind of fluids can the UVP be used?

The present model of UVP has been developed for flow in such liquids as:

  • Water
  • Organic liquids: Freon, Petroleum
  • Liquid metals: Mercury, Lead-Bismuth-Eutectic
  • Ferromagnetic liquid
  • Polymeric fluid
  • Food materials: Mayonnaise, Ketchup, Coffee, etc.

How is it possible to measure flow in vessel or pipe through the wall?

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.

What kind of materials can be used for the container wall on which a transducer is fixed?

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:

  • Water (1.48 MRay) - Plexiglas (3.15 MRay), PVC (3.27 MRay), thin glass (12 MRay)
  • Freon (1.12 MRay) - thin glass (12 MRay)
  • Mercury (19.6 MRay) - Aluminium (17.3 MRay), Stainless Steel (45.7 MRay)
  • Pb-Bi Eutectic (~20 MRay) - Aluminium (17.3 MRay)
  • Petroleum based ferromagnetic liquid (~1.4 MRay)- Plexiglas (3.15 MRay)
  • Water based thin slurry (1.48 MRay) - Plexiglas (3.15 MRay)


The following combinations need careful consideration:

  • Water (1.48 MRay) - Metal (20 - 50 MRay)
  • Mercury (19.6 MRay) - Glass (12 MRay)

How can the applicability of the method in certain media be tested?

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.

Is there any medium where UVP Monitor fails to measure?

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.

How can I measure water flow in relatively thick cast iron pipe?

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.