Lubricating fluid condition monitor

• US 5,754,055 A
• Filed: 01/04/1996
• Issued: 05/19/1998
• Est. Priority Date: 01/04/1996
• Status: Expired due to Fees

• Current Assignee: Alliant Techsystems Incorporated (Northrop Grumman Corporation)
• Original Assignee: Mission Research Corp (Northrop Grumman Corporation)
• Inventors: Catoe, William, Bollen, Michael W., Folen, Vince, McAdoo, John H., Volkening, Fred
• Primary Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US08/582,646
• Time in Patent Office: 866 Days
• Field of Search: 324/553, 324/602, 324/603, 324/630, 324/633, 324/636, 324/637, 324/639, 324/647, 340/603, 340/627, 340/631, 73/61.42
• US Class Current: 324/636
• CPC Class Codes: F01M 11/10 Indicating devices; Other safety devices
• CPC Class Codes: F16N 29/04 enabling a warning to be given; enabling moving parts to be stopped
• CPC Class Codes: G01N 22/02 Investigating the presence of flaws
• CPC Class Codes: G01N 33/2888 Lubricating oil characteristics, e.g. deterioration lubricating properties G01N33/30

Abstract

A lubricating/hydraulic fluid condition monitor in which a coaxial microwave resonator is placed in a fluid conduit to determine changes in the chemical properties and debris concentration is disclosed. Microwave radiation is applied to the resonator for measuring the resonant frequency and resonator Q. An externally powered electric or magnetic field is used to alternately align and misalign debris in the fluid while the resonator properties are being measured. A logic unit automatically generates tables of resonant frequency and Q versus resonator mode and external field strength. This set of tables constitutes a fingerprint of the fluid condition. By matching the fingerprint against a set of fingerprints taken under known conditions, the condition of the fluid is determined. Changes in the fluid'"'"'s dielectric constant caused by oxidation or the presence of water, changes in the concentration and size of conducting particles from bearing wear, and changes in viscosity all affect the fingerprint; and thus, can be monitored in real time. In a variation of the invention, a lumped-circuit resonator printed on a microwave circuit board is used as the sensor. In a further variation, a transmission-line resonator printed on a microwave circuit board is used as a sensor. In yet another variation the resonator is a lumped circuit waveguide structure through which the fluid flows. In still another variation, time domain reflectometry is used in a transmission line having one end immersed in the fluid.

Claims

1. A system for monitoring the condition of lubricating/hydraulic fluid comprising:

a lubricating/hydraulic system having lubricating/hydraulic fluid flowing in a conduit;

a microwave stripline resonator immersed in the fluid flowing in said conduit;

said microwave stripline resonator comprised of a loop inductor and interdigitized capacitor;

microwave oscillating means connected to said microwave resonator to apply microwave frequency radiation to said resonator;

means of r applying a varying electric or magnetic field to said lubricating/hydraulic fluid;

detecting means detecting changes in microwave radiation build-up within said microwave resonator;

logic means connected to said detecting means to analyze said changes in s aid microwave radiation;

said logic means determining the chemical and physical properties of said lubricating/hydraulic fluid from said changes in microwave radiation;

whereby said lubricating/hydraulic fluid monitoring system provides advance warning of deterioration of mechanical parts and helps pinpoint failure when it occurs.

2. The system according to claim 1 in which said capacitor has a capacitance of approximately 1 pF.

3. The system according to claim 1 in which said inductor is a 1 mm loop inductor.

4. The system according to claim 1 in which said microwave resonator has a resonant frequency of approximately 5 GHz.

5. The system according to claim 1 in which said logic means determines the dielectric constant of said lubricating/hydraulic fluid.

6. The system according to claim 1 in which said logic means determines concentration of conductive particles in said lubricating/hydraulic fluid.

7. The system according to claim 6 in which said logic means determines the concentration of conductive particles in said lubricating/hydraulic fluid from a data base made by comparing measurements made with said system to measurements made with well established laboratory instruments.

8. The system according to claim 6 in which said logic means determines the concentration of ferromagnetic particles in said lubricating/hydraulic fluid.

9. The system according to claim 8 in which said logic means measures the concentration of ferromagnetic particles in said lubricating/hydraulic fluid from a data base made by comparing measurements made with said system to measurements made with well established laboratory instruments.