CAVITATION DETECTION

• US 20100269574A1
• Filed: 07/25/2008
• Published: 10/28/2010
• Est. Priority Date: 07/27/2007
• Status: Active Grant

• Current Assignee: The United States of America As Represented By The Secretary of Commerce
• Original Assignee: The United States of America As Represented By The Secretary of Commerce
• Inventors: Zeqiri, Bajram
• Granted Patent: US 8,696,321 B2
• Time in Patent Office: Days
• US Class Current: 73/61.790
• CPC Class Codes: F04D 15/0088 Testing machines
• CPC Class Codes: F04D 29/669 especially adapted for liquid pumps F04D29/18 takes precedence
• CPC Class Codes: F05D 2270/333 Noise or sound levels
• CPC Class Codes: G01N 2291/02433 Gases in liquids, e.g. bubbles, foams
• CPC Class Codes: G01N 29/02 Analysing fluids using acoustic emission techniques G01N29/14 ; constructional or flow details for analysing fluids G01N29/222; optoacoustic fluid cells G01N29/2425
• CPC Class Codes: G01N 29/14 using acoustic emission techniques echo of particles G01N29/046; measuring mechanical vibrations or acoustic waves in solids in general G01H1/00
• CPC Class Codes: G01N 29/28 providing acoustic coupling , e.g. water impedance matching G10K11/02
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency
• CPC Class Codes: G01N 29/4436 with a reference signal amplitude comparison G01N29/48
• CPC Class Codes: Y10T 137/7759 Responsive to change in rate of fluid flow

Abstract

There is disclosed an apparatus and method for detecting cavitation in fluid machines, for example pumps (100). In one embodiment a piezoelectric gasket (102) is used as a sensor to sense cavitation. In some embodiments highpass filters (302), (501) are used to detect ultrasonic acoustic signals in about the MHz range. If the energy in the MHz range is excessive then cavitation is deemed to be occurring and the speed of a motor (110) may be reduced in proportion to the degree of cavitation deemed to be occurring. In another embodiment (FIG. 5) the energy in the MHz range is normalised against the energy in the kHz range. Other sensors (600, 701) are also disclosed.

Claims

1. A system for detecting and controlling the occurrence of cavitation during operation of a fluid mechanism, comprising:

an acoustic sensor;

a highpass filter having a cut-off frequency greater than or equal to 1 MHz for filtering a signal from the acoustic sensor;

a first detector for providing a signal indicative of the energy in the highpass filtered signal from the acoustic sensor;

a reference receiver for receiving a reference value signal;

a comparator for comparing the signal from the first detector with the reference value signal and providing an indication if the signal from the first detector exceeds the reference value signal; and

a controller operable to control an operating condition of a fluid mechanism to reduce cavitation in the event that the comparator indicates that the signal from the first detector exceeds the reference value signal.

2. A system according to claim 1, comprising an amplifier to amplify the signal from the acoustic sensor.

4. A system according to claim 1, wherein the highpass filter forms part of a bandpass filter comprising a lowpass filter.

5. A system according to claim 4, wherein the lowpass filter comprises an upper response frequency of the acoustic sensor.

6. A system according to claim 4, wherein the cutoff frequency of the lowpass filter section of the bandpass filter is 5 MHz or 20 MHz.

7. A system according to claim 1, comprising:

a lowpass filter for filtering a signal from the acoustic sensor; and

a second detector for providing a signal indicative of the energy in the lowpass filtered signal from the acoustic sensor,

wherein the reference receiver is arranged to receive the signal from the second detector as the reference value signal.

8. A system according to claim 7, wherein the lowpass filter has a cutoff frequency of at most one of IkHz, 1OkHz, 10OkHz and IMHz.

10. A system according to claim 1, wherein the controller comprises a motor controller and wherein the motor controller is operable to reduce the speed of a motor in the event that the signal from the first detector exceeds the reference value signal.

11. A system according to claim 10, comprising a motor.

12. A system according to claim 11, comprising a pump connected to the motor, wherein the acoustic sensor is located relative to the pump to sense cavitation occurring within the pump.

13. A system according to claim 1, wherein the acoustic sensor comprises a gasket comprising a piezoelectric material.

14. A system according to claim 13, wherein the piezoelectric material comprises a polymer piezoelectric material.

15. A system according to claim 14, wherein the gasket comprises PVDF.

16. A system according to claim 13, wherein the gasket is located at an inlet to a pump.

17. A system according to claim 1, wherein the acoustic sensor comprises an acoustic rubber coupler, one or more polymer piezoelectric layers and a grip portion.

18. A system according to claim 17, wherein the acoustic rubber coupler comprises rubber having a Shore hardness in the range 10 to 20.

19. A system according to claim 1, wherein the acoustic sensor is provided in a recess in a casing of a pump.

3. (canceled)

9. (canceled)

20. An acoustic sensor comprising a gasket comprising a polymer piezoelectric material.

21. An acoustic sensor comprising an acoustic coupler, one or more polymer piezoelectric layers and a grip portion.

22. A pump having an acoustic sensor provided in a recess in a casing of the pump.

23. (canceled)

24. (canceled)

25. (canceled)

26. A method of detecting and controlling the occurrence of cavitation in a fluid machine, comprising the steps of:

receiving a signal from an acoustic sensor that is acoustically coupled to the fluid machine;

high pass filtering the signal from the acoustic sensor by means of a high pass filter having a cut-off frequency greater than or equal to 1 MHz;

providing a signal indicative of the energy in the high pass filtered signal from the acoustic sensor;

comparing the signal indicative of the energy with a reference value signal and providing an indication if the signal indicative of the energy exceeds the reference value signal; and

controlling an operating condition of a fluid mechanism to reduce cavitation in the event that the comparator indicates that the signal from the first detector exceeds the reference value signal.