ELECTROCHEMICAL IMPEDANCE MEASUREMENT SYSTEM AND METHOD FOR USE THEREOF

• US 20080054914A1
• Filed: 05/14/2007
• Published: 03/06/2008
• 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: Byington, Carl, Watson, Matthew, Brewer, Ryan
• Granted Patent: US 7,504,835 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

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

injecting a broadband signal for impedance measurement, wherein the broadband signal provides an assessment of impedance over a range of frequencies and where the range of frequencies is at least a decade of frequencies;

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, wherein the analysis further includes

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

subsequently re-assembling the signals; and

storing at least one characteristic of the fluid.

2. A method for predicting fluid quality and degradation in a fluid system, comprising:

injecting a broadband signal for impedance measurement, wherein the broadband signal provides an assessment of impedance over a range of frequencies and where the range of frequencies is at least a decade of frequencies;

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, wherein the analysis 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, and

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; and

storing at least one characteristic of the fluid.

3. A method for sensing electrochemical impedance of a fluid, comprising:

injecting an AC broadband, composite interrogation signal consisting of multiple frequencies overlaid upon each other within a composite waveform into the fluid;

simultaneously measuring both the interrogation and fluid response signals;

interpreting the combined response in the composite interrogation and response signals to generate the electrochemical impedance of the fluid; and

storing data representing at least the electrochemical impedance of the fluid.

4. The method of claim 3, further comprising measuring the impedance of the fluid in situ.

5. The method of claim 3, wherein the fluid is selected from the group consisting of:

fuels, lubricants, coolants and hydraulic fluids.

6. The method of claim 3, wherein the electrochemical impedance is used as an indication of fluid quality.

7. The method of claim 3, wherein interpreting the combined response includes the step of determining both magnitude and phase changes in the response signals.

13. The method of claim 3, wherein the impedance of the fluid (Z_OIL) is calculated as:

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

14. The method of claim 3, wherein 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.

15. The method of claim 3, further comprising applying a scaling value to the composite interrogation signal, wherein the scaling value is selected such that a full dynamic range of a digital to analog converter is used to output the composite interrogation signal.

16. The method of claim 3, further including determining the type of fluid contamination.

17. The method of claim 3, further including quantifying at least one level of contamination within the fluid.

18. The method of claim 3, wherein at least one composite interrogation signal is created for each frequency range of interest.

19. The method of claim 18, wherein interpreting the combined response further includes:

assessing the signals indicative of impedance for each range of frequencies independently; and

subsequently re-assembling the signals.

20. The method of claim 18, wherein the formula for generating the interrogation signal, w_D(t), includes

$w_D$

( 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.

21. The method of claim 3, 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 is utilized for each range of the composite interrogation signals to output the composite interrogation signals.

22. The method of claim 3, wherein 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; and

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.

8. A method for sensing electrochemical impedance of a fluid, comprising:

injecting an interrogation signal into the fluid, wherein the interrogation signal is a broadband voltage signal comprising a plurality of logarithmically-spaced frequencies, and where at least one interrogation signal is created for each frequency range of interest;

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

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

storing data representing at least the electrochemical impedance.

9. The method of claim 8, wherein each frequency range spans a decade of frequencies.

10. The method of claim 9, wherein the detecting step further includes:

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

subsequently re-assembling the signals.

11. The method of claim 9, wherein the formula for generating the interrogation signal, w_D(t), includes

$w_D$

( 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 wD(t), and N is the number of log-spaced signal frequencies.

12. The method of claim 11, 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.