The Ultrasonic Flow Measuring Principle — Transcript

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1. 0:16The most diverse substances are transported and  distributed in piping systems every single day.
2. 0:23They can include solvents and chemicals,  vegetable oils in the food sector,
3. 0:30coolants in primary industry  or petrochemical products.
4. 0:36The fluids flowing through pipes often have  completely different properties. Therefore,
5. 0:42different principles are  required for their measurement.
6. 0:46One principle is flow measurement based on the  differential transit time method using ultrasound.
7. 0:55The basic physics of this principle can be traced
8. 0:57back to the English physicist and  Nobel prize winner Lord Raleigh.
9. 1:02His book "Theory of Sound“ – published
10. 1:05in 1877 – describes the propagation  of sound waves in solids and gases.
11. 1:13Here is how this measurement method works.
12. 1:20Inside the ultrasonic flowmeter, pairs of sensors
13. 1:24are fitted across from each  other in the measuring tube.
14. 1:28Each individual sensor can alternately transmit  and receive an ultrasonic signal. Simultaneously,
15. 1:35the transit times of these signals are measured.
16. 1:39The ultrasonic signals are  generated with piezoelectrical
17. 1:44crystals applying a voltage. Conversely,  a piezoelectric crystal creates a voltage,
18. 1:50when an ultrasonic signal impacts the sensor.
19. 1:55By increasing the number of sensor pairs  it is possible to accurately detect and
20. 2:00mathematically compensate for flow profile  distortions over the entire pipe cross section.
21. 2:07When there is no flow condition, the signal transit  times are the same – upstream and downstream.
22. 2:14Once the fluid starts to flow in  the measuring tube, the ultrasonic
23. 2:18signals are accelerated in the direction  of flow and decelerated against the flow.
24. 2:24As a result, the ultrasonic signals now  have different transit times – less time
25. 2:30in the direction of flow and  more time against the flow.
26. 2:34Therefore, the differential  transit time measured by the
27. 2:37sensors is directly proportional  to the flow velocity in the pipe.
28. 2:43Together with the known tube cross-section,  the actual flow volume can then be calculated.
29. 2:50The greater the flow velocity,
30. 2:52the greater the measured time difference  between the two ultrasonic signals.
31. 2:59For ultrasonic flow measurement, the sensors don’t  necessarily have to be fitted into the pipe wall.
32. 3:07With a clamp-on system, for example, the sensors  are fastened directly onto the outside of the
33. 3:14pipe. They can be retrofitted at  any time without interrupting the process.
34. 3:21With clamp-on sensors, the ultrasonic signal  is passed directly through the pipe wall and
35. 3:27into the fluid. The signal continues through the fluid, is reflected on the opposite pipe
36. 3:33wall and then measured by the second sensor – in  this example with a two-traverse installation.
37. 3:40The clamp-on design is unique because flow rates  can be measured in very large pipes up to 4
38. 3:47meters in diameter. This possibility increases the areas of application,
39. 3:53for example in the water  and hydroelectric industries.
40. 4:03Flexible mounting, process  safety and cost-effectiveness
41. 4:07are the distinctive advantages  of ultrasonic flow measurement.
42. 4:18For all applications, we have the right solution.
43. 4:23Endress+Hauser – your single-source  supplier for measurement technology!