Electrochemical impedance measurement system and method for use thereof

• US 20050104607A1
• Filed: 11/12/2004
• Published: 05/19/2005
• Est. Priority Date: 11/14/2003
• Status: Active Grant

• Current Assignee: Sikorsky Aircraft Corporation (Martin Marietta Corporation)
• Original Assignee: Impact Technologies LLC (Martin Marietta Corporation)
• Inventors: Watson, Matthew J., Brewer, Ryan C., Byington, Carl S.
• Granted Patent: US 7,239,155 B2
• Time in Patent Office: Days
• US Class Current: 324/693
• CPC Class Codes: G01N 27/026 Dielectric impedance spectroscopy electrochemical impedance spectroscopy for measuring corrosion G01N17/02
• CPC Class Codes: G01N 33/2888 Lubricating oil characteristics, e.g. deterioration lubricating properties G01N33/30

Abstract

Disclosed is a method and apparatus for an electrochemical impedance measurement, and in particular circuitry and components employed for such measurements. The system employs an injected broadband AC signal to produce an associated response signal. The subsequent analysis of injected and response signals, considering both magnitude and phase, gives broadband impedance and therefore fluid characteristic information. An embodiment described is relative to a smart oil sensor system suitable for sensing, analyzing and reporting the condition of oil or other liquids used in equipment and machinery.

Claims

17. A method for sensing changes in electrochemical impedance of a fluid, comprising the steps of:

injecting an interrogation signal into the fluid;

detecting, as a response signal, a response to the interrogation signal passed through the fluid; and

interpreting the combined response in interrogation and response signal variations to determine the electrochemical impedance.

1. A method for predicting fluid quality and degradation in a fluid system, comprising the steps of:

measuring a low-powered, broadband, AC impedance for a fluid and generating signals indicative of the impedance;

conducting an analysis of the measured impedance signals to infer a characteristic of the fluid and its constituent components.

2. The method of claim 1, further comprising the step of predicting, in response to the analysis of the measured impedance signals, the fluid quality.

3. The method of claim 1, further comprising the step of monitoring the condition of the fluid in real-time.

4. The method of claim 1, further comprising the step of monitoring the condition of the fluid in situ.

5. The method of claim 1, wherein the fluid is selected from the group consisting of:

fuels, lubricants, coolants and hydraulic fluids.

6. The method of claim 1, further comprising the steps of:

measuring the low-powered, broadband, AC impedance for a plurality of fluid types and generating signals indicative of their impedances;

collecting the signals indicative of their impedances;

storing the signals indicative of their impedances; and

subsequently processing the stored impedance signals to determine at least one characteristic for each of the plurality of fluid types.

7. The method of claim 6, wherein the step of collecting the signals is accomplished using a computing device with a data acquisition capability.

8. The method of claim 7, wherein the computing device is handheld.

9. The method of claim 7, wherein the computing device is embedded.

10. The method of claim 1, further including the step of injecting a broadband signal for impedance measurement, wherein the broadband signal provides an assessment of impedance over a range of frequencies.

11. The method of claim 10, wherein the range of frequencies is at least a decade of frequencies.

12. The method of claim 1, further including the step of injecting a broadband signal for impedance measurement, wherein the broadband signal provides an assessment of impedance over a plurality of frequencies.

13. The method of claim 12, wherein the plurality of frequencies are logarithmically spaced over a range of frequencies.

14. The method of claim 10, wherein the step of conducting an analysis of the measured impedance signals includes comparing an interrogation signal to a response signal, and uses both magnitude and phase changes of the signals in the analysis.

15. The method of claim 11, wherein the analysis step further includes:

assessing the signals indicative of impedance for each decade independently; and

subsequently re-assembling the signals.

16. The method of claim 14, wherein the step of conducting an analysis of the measured impedance signals further comprises:

windowing a portion of the input signal and output response signal for a common time interval;

taking a Fast Fourier Transform of the two signals;

locating the peaks in the frequency domain at each of the frequencies of s the resultants waveform, wherein phase and magnitude signals of the input and output voltages for the signals are then converted into complex values and the impedance of the fluid is calculated.

18. The method of claim 17, further comprising the step of monitoring the condition of the fluid in situ.

19. The method of claim 17, wherein the fluid is selected from the group consisting of:

fuels, lubricants, coolants and hydraulic fluids.

20. The method of claim 17, wherein the electrochemical impedance is used as an indication of fluid quality.

21. The method of claim 17, wherein the interrogation signal is a broadband voltage signal.

22. The method of claim 17, wherein the step of interpreting the combined response includes the step of determining both magnitude and phase changes in the response signals.

23. The method of claim 21, wherein the interrogation signal is created by combining a plurality of discrete waveforms to create a broadband, composite signal.

24. The method of claim 21, wherein the broadband interrogation signal comprises a plurality of logarithmically-spaced frequencies.

25. The method of claim 24, wherein at least one interrogation signal is created for each frequency range of interest.

26. The method of claim 25, wherein each frequency range spans a decade of frequencies.

27. The method of claim 26, wherein the detecting step further includes:

assessing the signals indicative of impedance for each decade independently; and

subsequently re-assembling the signals.

28. The method of claim 26, wherein the formula for generating the interrogation signal, w_D(t), includes

$\begin{array}{c}{w}_D\end{array}$

( t ) = A ·

∑

n = 0 N - 1 ⁢

 

⁢

sin ⁡

( 2 ⁢

π

·

10 ( D + n N - 1 ) ·

t ) ,  

where A is a scaling value used to obtain the desired magnitude, D defines the decade of frequencies spanned by w_D(t), and N is the number of log-spaced signal frequencies.

29. The method of claim 28, wherein the scaling value, A, is selected such that the full dynamic range of a digital to analog converter used to output the interrogation signal, is utilized.

30. The method of claim 21, wherein a scaling value is applied, and where the scaling value is selected such that the full dynamic range of a digital to analog converter used to output the interrogation signal is utilized.

31. The method of claim 17, further comprising the step of using an interrogation signal (V_IN) and a response signal (V_OUT), to compute complex impedances.

32. The method of claim 22, wherein the step of interpreting the combined response further comprises:

windowing a portion of the interrogation signal and response signal for a common time interval;

taking a Fast Fourier Transform of the two signals;

locating the peaks in the frequency domain at each of the frequencies of the resultants waveform, wherein phase and magnitude signals of the input and output voltages for the signals are then converted into complex values and the impedance of the fluid is calculated.

33. The method of claim 26, wherein an impedance of the sample fluid (Z_OIL) is calculated as:

$Z_{\mathrm{OIL}}<br><br>\left(\mathrm{\omega <br><br>}\right)=\frac{V_{\mathrm{IN}}<br><br>\left(\mathrm{\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)-V_{\mathrm{OUT}}<br><br>\left(\mathrm{\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t-\mathrm{\varphi <br><br>}\right)}{V_{\mathrm{OUT}}<br><br>\left(\mathrm{\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t-\mathrm{\varphi <br><br>}\right)}·<br><br>R-Z_{\mathrm{SENSOR}}$

34. The method of claim 17, wherein the step of analyzing the variations in the response signal includes assessing impedance of the fluid over a wide range of frequencies, so as to capture the total impedance response of the system.

35. The method of claim 17, wherein the step of detecting a response to the interrogation signal is accomplished using a computing device with a data acquisition capability.

31-1. The method of claim 17, wherein the response signal is detected as a measured broadband response.

36. A system for sensing changes in the electrochemical impedance of a fluid, comprising:

means for generating an interrogation signal for injection into the fluid;

means for measuring a response to the interrogation signal passed through the fluid; and

means for processing the measured voltage variations in the response signal.

37. The system of claim 36, wherein the electrochemical impedance is used as an indication of fluid quality.

38. The system of claim 36, wherein the means for generating an interrogation signal includes circuitry and associated control logic for generating an interrogation signal

39. The system of claim 38, wherein the means for generating an interrogation signal is further capable of generating such a signal with log-spaced tones.

40. The system of claim 36, wherein the processing means is embedded.

41. The system of claim 36, wherein the means for measuring a response uses a sensor as a transmission channel for the input AC signal.

42. The system of claim 36, wherein a printed circuit board includes said means for generating an interrogation signal and said means for measuring a response to the interrogation signal.

43. The system of claim 42, wherein the printed circuit board includes:

an isolated power supply;

instrumentation amplifiers, filters, and low-level analog circuitry, all of which are placed on a board; and

unused portions of the board are filled with grounded copper.

44. The system of claim 41, wherein the sensor includes an electronics housing, at least a portion of which is electrically conductive so as to provide shielding against electrical noise.

45. The system of claim 44, wherein the sensor further includes at least a pair of flat-plate electrodes made of a conductive material.

46. The system of claim 41, wherein the sensor further includes at least one set of electrodes having a geometry, selected from the group of geometries consisting of:

parallel lines;

parallel plates;

parallel wires;

a point source and plate; and

combinations thereof.