Method and apparatus for the debris particulate characterizaion in lubricants

• US 20030132740A1
• Filed: 10/28/2002
• Published: 07/17/2003
• Est. Priority Date: 02/16/2000
• Status: Active Grant

• Current Assignee: Kaiku Process Solutions Limited
• Original Assignee: Kaiku Limited
• Inventors: Stone, Richard, Dowdeswell, Richard Mark, Amrani, Mohammed El Hassan
• Granted Patent: US 6,949,936 B2
• Time in Patent Office: Days
• US Class Current: 324/71.4
• CPC Class Codes: G01N 33/2858 metal particles

Abstract

The present invention relates to an apparatus and method for measuring a particulate characteristic of a particulate-containing fluid, in particular for monitoring the particulate content of lubricating or hydraulic fluids in a mechanical system in order to diagnose component failure.

Claims

1. A method for measuring a particulate characteristic of a fluid, said method comprising the steps of:

applying an electrical signal at one or more frequencies to the fluid, wherein the one or more frequencies includes the resonant frequency;

measuring an impedance quantity characteristic of the fluid at the one or more frequencies; and

deducing the particulate characteristic from the measured impedance quantity.

2. A method as claimed in claim 1 wherein the fluid is a liquid.

3. A method as claimed in claim 1 or 2 wherein the fluid is a lubricating fluid or hydraulic fluid.

4. A method as claimed in any preceding claim wherein the particulate characteristic is selected from the group consisting of (a) the presence or absence of the particulate (b) the extent of the presence of the particulate (c) a change in the presence of the particulate and (d) the extent of a change in the presence of the particulate.

5. A method as claimed in any preceding claim wherein the particulate characteristic of the fluid is a physical indicator of the status of a static or dynamic system in which the fluid is present.

6. A method as claimed in any preceding claim wherein the particulate characteristic is the presence or absence of a particulate in the fluid.

7. A method as claimed in any preceding claim wherein the particulate characteristic is the amount of a particulate in the fluid.

8. A method as claimed in claim 7 wherein the particulate characteristic is the particle size distribution.

9. A method as claimed in any of claims 1 to 5 wherein the particulate characteristic is a change in the particle size distribution.

10. A method as claimed in claim 1 comprising the steps of:

measuring at the one or more frequencies the impedance quantity characteristic of the fluid at a time t₂;

measuring at the one or more frequencies the impedance quantity characteristic of the fluid at a time t₂;

deducing a change in the characteristic of the fluid between time t₁, and t₂; and

correlating the change in the characteristic of the fluid with a change in the fluid environment.

11. A method as claimed in claim 1 comprising:

measuring the impedance quantity at a number of discrete times over an extended temporal range.

12. A method as claimed in claim 11 comprising:

measuring the impedance quantity continuously so as to provide real time analysis of the fluid environment.

13. A method as claimed in claim 1 further comprising the initial steps of:

applying an electrical signal at one or more frequencies to a calibrant fluid;

measuring an impedance quantity at one or more

correlating the measured impedance quantity with a particulate characteristic of the calibrant fluid, wherein the particulate characteristic of the calibrant fluid is known.

14. A method as claimed in claim 13 wherein the calibrant. fluid is a fluid containing a known particulate.

15. A method as claimed in claim 13 wherein the calibrant fluid is a fluid containing a particulate at a known particulate concentration.

16. A method as claimed in claim 13 wherein the calibrant fluid is a fluid containing a known particulate distribution.

17. A method as claimed in any preceding claim wherein the electrical signal is applied to the fluid at a single frequency and the impedance quantity of the fluid is measured at that single frequency.

18. A method as claimed in claim 17 wherein the single frequency is at or near to the resonant frequency.

19. A method as claimed in any preceding claim comprising:

applying an electrical signal to the fluid at each of a plurality of frequencies in a frequency range; and

measuring an impedance quantity at each of the plurality of frequencies in the frequency range.

20. A method as claimed in claim 19 wherein the plurality of frequencies in the frequency range are sufficient in number to generate an impedance spectrum characteristic of the fluid.

21. A method as claimed in any preceding claim wherein the impedance quantity is a dissipation factor.

22. A method as claimed in any preceding claim wherein the electrical signal is a time varying electrical signal.

23. An apparatus for measuring a particulate characteristic of a fluid comprising;

electrical signal applying means adapted to apply an electrical signal at one or more frequencies to the fluid, wherein the one or more frequencies includes the resonant frequency;

measuring means for measuring an impedance quantity characteristic of the fluid at the one or more frequencies; and

means for deducing the particulate characteristic from the measured impedance quantity.

24. An apparatus as claimed in claim 23 wherein the electrical signal applying means is adapted to apply a time varying electrical signal to the fluid at one or more frequencies in a frequency range.

25. An apparatus as claimed in claim 23 or 24 comprising at least two electrodes capable of being positioned in direct or indirect electrical contact with the fluid.

26. An apparatus as claimed in any of claims 23 to 25 wherein the electrical signal applying means comprises a probe adapted to be inserted into a mechanical system so as to enable measurement of the impedance spectrum characteristic of a fluid within the mechanical system.

27. An apparatus as claimed in any of claims 23 to 26 wherein the measuring means comprises an impedance analyser.

28. Use of an apparatus as defined in any of claims 23 to 27 for diagnosing failure of a mechanical system.