Electrical measurement of oil quality

• US 6,459,995 B1
• Filed: 05/04/2000
• Issued: 10/01/2002
• Est. Priority Date: 05/07/1997
• Status: Expired due to Term

• Current Assignee: Lubrigard Limited
• Original Assignee: Lubrigard Limited
• Inventors: Collister, Christopher John
• Primary Examiner(s): Hilten, John S.
• Assistant Examiner(s): Vo, Hien
• Application Number:
  US09/423,478
• Time in Patent Office: 880 Days
• Field of Search: 702/23, 702/24, 702/25, 702/104, 733/04.C, 73/540.1, 73/540.2, 73/540.5, 73/614.4, 73/616.1, 73/614.3, 324/665, 324/670, 324/678, 324/689, 324/655, 324/668, 324/663, 324/682, 324/683, 324/675, 324/76.79, 324/662, 324/664, 324/671, 340/620, 340/439, 340/450.3, 340/618, 340/631
• US Class Current: 702/23
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/2888 Lubricating oil characteristics, e.g. deterioration lubricating properties G01N33/30

Abstract

Method and apparatus for measuring oil quality based on the permittivity of the oil comprising a capacitive or radiative sensor for exposure to the oil, and an oscillator circuit including the sensor, wherein the oscillator circuit comprises a LC or crystal oscillator which provides an output signal, the amplitude of which is dependent upon the lossiness of the Tan δ of the oil, and a measuring device that responds to the amplitude of the output signal as a measure of oil quality.

Claims

1. Apparatus for measuring oil quality based on the permittivity (dielectrical coefficient) of the oil comprising a capacitive sensor for exposure to the oil, and an oscillator circuit including the sensor, characterised in that the oscillator circuit comprises one of a LC or crystal oscillator and provides an output signal, an amplitude of which is dependent upon a lossiness Tan δ

of the oil, and a measuring device that responds to the amplitude of said output signal as a measure of oil quality.

2. Apparatus as claimed in claim 1, in which the oscillator circuit is such that it draws a current which changes with the lossiness Tan δ

of the oil and gives a measure of oil quality.

3. Apparatus as claimed in claim 1, in which the amplitude is substantially inversely proportional to Tan δ

.

4. Apparatus as claimed in claim 1, in which the sensor is incorporated in a sensor head adapted for fitting to one of an engine, machine filter or probe so as to be exposed to said oil.

5. Apparatus as claimed in claim 4, in which the oscillator circuit is incorporated in the sensor head.

6. Apparatus as claimed in claim 4, in which a temperature sensor is incorporated in the sensor head and produces a temperature output signal which is passed to the measuring means so as to allow temperature compensation in the output signal.

7. Apparatus as claimed in claim 6, in which the measuring means incorporates a processor and memory that incorporates a look-up table of temperature compensation values that are accessed by the processor according to the output signal and temperature output signal received by the processor.

8. Apparatus as claimed in claim 4, in which the sensor is mounted at the end of a long hollow flexible probe suitable for insertion into an orifice for testing oil.

9. Apparatus as claimed in claim 1, in which the measuring device includes a calibrator which is operable to cause a baseline value of the output signal to be saved in memory for reference in determining oil quality from subsequent values of the output signal.

10. Apparatus as claimed in claim 9, in which the memory is such as to retain stored values when power is disconnected.

11. Apparatus as claimed in claim 10, in which multiple sequential values based on the output signal are stored in the memory for subsequent downloading.

12. Apparatus as claimed in claim 1, in which the measuring device includes a display that displays an indication of oil quality.

13. Apparatus as claimed in claim 1, in which the output signal is suitable for interfacing with a data bus.

14. Apparatus as claimed in claim 1, in which the sensor comprises one or more capacitor plates pierced with openings to facilitate ingress of oil.

15. Apparatus as claimed in claim 14, comprising a pair of concentric capacitor plates.

16. Apparatus as claimed in claim 1, in which the sensor is intended to radiate into the oil dielectric medium like a short antenna or dielectric probe.

17. An oil bypass filter for attachment to an engine incorporating apparatus as claimed in claim 1.

18. A method of measuring oil quality based on the permittivity of the oil using an oscillator circuit including a capacitive sensor, characterised in that the sensor is one of a LC or crystal oscillator circuit and provides and output signal, an amplitude of which is dependent upon a lossiness Tan δ

of the oil, and it is used to give a measure of oil quality.