Absolute property measurements using electromagnetic sensors

• US 20050127908A1
• Filed: 10/12/2004
• Published: 06/16/2005
• Est. Priority Date: 10/10/2003
• Status: Active Grant

• Current Assignee: Jentek Sensors, Inc.
• Original Assignee: Jentek Sensors, Inc.
• Inventors: Goldfine, Neil J., Grundy, David C., Schlicker, Darrell E., Washabaugh, Andrew P., Zilberstein, Vladimir A., Lyons, Robert J., Shay, Ian C., Tsukernik, Vladimir, Windoloski, Mark D.
• Granted Patent: US 7,696,748 B2
• Time in Patent Office: Days
• US Class Current: 324/240
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G01N 27/9046 by analysing electrical signals

Abstract

Methods and apparatus are described for absolute electrical property measurement of materials. This is accomplished with magnetic and electric field based sensors and sensor array geometries that can be modeled accurately and with impedance instrumentation that permits accurate measurements of the in-phase and quadrature phase signal components. A dithering calibration method is also described which allows the measurement to account for background material noise variations. Methods are also described for accounting for noise factors in sensor design and selection of the optimal operating conditions which can minimize the error bounds for material property estimates. Example application of these methods to automated engine disk slot inspection and assessment of the mechanical condition of dielectric materials are presented.

Claims

1. A method for accounting for conductor thicknesses in a sensor having at least one conductor acting as a drive to create a field for interrogating a test material and terminals for conductor connection to electrical instrumentation, said method comprising:

forming a layered model of a sensor conductor geometry and the test material proximate to the sensor, the model including mathematical expressions that describe the physical behavior of the sensor and interactions with the test material;

dividing cross-sectional thickness of the drive geometry into multiple layers;

assigning source values across each layer of the drive; and

relating the source values to terminal values that can be measured with the instrumentation.

2. The method as claimed in claim 1 wherein the sensor is an electromagnetic sensor.

3. The method as claimed in claim 2 wherein the field is a magnetic field.

4. The method as claimed in claim 2 wherein the field is an electric field.

5. The method as claimed in claim 1 wherein the source is an electrical current.

6. The method as claimed in claim 1 wherein the source is an electrical voltage.

7. The method as claimed in claim 1 further comprising:

sensing the created field with at least one additional conductor.

8. The method as claimed in claim 7 wherein the drive and sense conductors are in the same plane.

9. The method as claimed in claim 7 wherein the drive and sense conductors are in different planes.

10. A method for measuring electrical impedance comprising:

passing an excitation signal having a frequency, amplitude, and phase set by a signal generator controlled by a master microcontroller into a test circuit;

creating a first reference signal with a second signal generator that has the same frequency as the excitation signal;

combining said reference signal with at least one electrical signal from the test circuit using a data acquisition channel that contains a microcontroller; and

transmitting acquired measurement data to a host computer for processing and storing measured values.

11. The method as claimed in claim 10 further comprising:

switching a phase of the reference signal between 0 and 90 degrees.

12. The method as claimed in claim 10 further comprising:

creating a second reference signal that is 90 degrees out of phase with the first reference signal.

13. The method as claimed in claim 12 further comprising:

adding at least one additional data acquisition channel so that in-phase and quadrature-phase components of the test circuit signal can be determined in parallel.

14. A method for calibrating a sensor comprising:

placing a sensor proximate to a reference material; and

measuring the response of the sensor as the sensor is moved over the surface of the reference material for one or more operating conditions.

15. The method as claimed in claim 14 wherein the sensor is a magnetic field sensor.

16. The method as claimed in claim 14 wherein the sensor is an electric field sensor.

17. The method as claimed in claim 14 wherein the motion is constant in one direction.

18. The method as claimed in claim 14 wherein the motion is a back and forth dithering motion.

19. The method as claimed in claim 14 wherein the sensor has a least one linear array of elements.

20. The method as claimed in claim 19 wherein the motion is in a direction parallel to the array of elements.

21. The method as claimed in claim 20 wherein the response for each element is measured over the same test material location.

22. The method as claimed in claim 14 wherein the operating conditions are with and without a shim.

23. The method as claimed in claim 14 wherein the operating conditions are at multiple frequencies.

24. The method as claimed in claim 14 wherein the motion is translation.

25. The method as claimed in claim 14 wherein the motion is rotation.

26-32. -32. (canceled)

33. A method of using an eddy current sensor array comprising:

(a) placing an engine disk on a turntable having a pneumatic cylinder;

(b) placing a shuttle inside an engine disk slot, the shuttle containing a flexible eddy current sensor array that conforms to the slot material surface and a balloon behind the sensor;

(c) measuring the sensor array response as the shuttle is scanned through the slot;

(d) rotating the engine disk to the next slot position after scanning the slot;

(e) using a single motor to control both the disk rotation and shuttle scanning;

(f) deflating the balloon prior to entry into the slot;

(g) repeating steps (b) through (f) for each slot;

(h) timing operation so that all of the data is recorded automatically,

(i) converting the sensor array response into electrical conductivity and lift-off data; and

(j) displaying the conductivity and lift-off data.

34. The method as claimed in claim 33 wherein the data is displayed as an image or a C-scan.

35. The method as claimed in claim 33 wherein the data is displayed as a plot or a B-scan.

36. The method as claimed in claim 33 further comprising:

placing a sacrificial coating between the sensor and the slot material surface.

37. The method as claimed in claim 35 wherein the lift-off data provides a diagnostic for wear in sacrificial coating.

38. The method as claimed in claim 33 further comprising:

calibrating the sensor array response with a reference measurement in air.

39. The method as claimed in claim 33 further comprising:

calibrating the sensor array response with a reference measurement on a reference material.

40. The method as claimed in claim 33 further comprising:

normalizing the sensor array response using measurements in the center of a slot.

41-93. -93. (canceled)