DETERMINING THE RESONANCE PARAMETERS FOR MECHANICAL OSCILLATORS

• US 20100324852A1
• Filed: 06/02/2010
• Published: 12/23/2010
• Est. Priority Date: 06/23/2009
• Status: Active Grant

• Current Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Original Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Inventors: Yablon, Dalia G., Mathez, Yvonne, Cheng, Chung-Min, Schilowitz, Alan M., Akehurst, George, Wolf, H. Alan, Alvarez, Manuel S.
• Granted Patent: US 8,676,543 B2
• Time in Patent Office: Days
• US Class Current: 702/104
• CPC Class Codes: G01D 1/00 Measuring arrangements giving results other than momentary value of variable, of general application G01D3/00 takes precedence; in tariff metering apparatus G01D4/00; transducers not specially adapted for a specific variable G01D5/00
• CPC Class Codes: G01D 15/00 Component parts of recorders for measuring arrangements not specially adapted for a specific variable
• CPC Class Codes: G01H 13/00 Measuring resonant frequency
• CPC Class Codes: G01N 17/04 Corrosion probes
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

The prior art describes the application of mechanical oscillators for the measurement of corrosion and/or deposition. Mechanical oscillators employ the use of resonance parameters, frequency and the quality factor Q, for the measurement of corrosion or deposition. However, the prior art does not consider the required precision for measuring frequency or Q in the presence of noise to make these measurements. In particular, the ability of the mechanical oscillator to measure small amounts of metal loss or deposition is not only dependent upon the mechanical design but is limited by the precision in determining the resonance frequency and Q. The present invention discloses methods for measuring these resonance parameters with a high precision in the presence of noise. This degree of precision is required to maximize the utility of these devices as sensitive probes for corrosion and deposition (fouling) measurement. All of the embodiments described herein employ curve fitting consistent with modeling the mechanical oscillator as a simple harmonic oscillator. This curve fitting procedure, combined with averaging and utilizing signal processing parameters to mitigate noise effects, adds considerable precision in measuring resonance parameters.

Claims

1. A method for determining the resonance parameters (f, Q resonance frequency and quality factor) for a mechanical oscillator in the presence of noise comprising:

a) exciting the mechanical oscillator in the environment that produces the noise causing an excitation;

b) determining a response to said excitation; and

c) determining f and Q from said response with multiple measurements and curve fitting and averaging.

2. The method of claim 1 wherein said response is a function of frequency and/or time.

3. The method of claim 2 wherein response is a function of frequency.

4. The method of claim 2 wherein response is a function of time.

5. The method of claim 1 wherein the determination of step b) is accomplished with a digital computer

6. The method of claim 1 wherein step a) is produced by flow of the environment.

7. The method of claim 1 wherein step a) is produced by an external source (signal generator).

8. The method of claim 6 wherein f and Q are determined from the steps of determining a fast fourier transform of amplitude as a function of frequency, wherein said f and Q are determined from averaging the fast fourier transform run multiple times.

9. The method of claim 7 wherein f and Q are determined from the steps of terminating said external source so that the amplitude of said oscillator decreases from which amplitude as a function of excitation frequency is determined repeating this step so as to obtain an average value off and Q.

10. The method of claim 7 wherein f and Q are determined from the steps of terminating said external source so that the amplitude of said oscillator decreases, obtaining f from the crossing of the amplitude of zero and Q from the decline of the amplitude, repeating the above steps to obtain an average value for f and Q.

11. The method of claim 10 wherein f and Q are determined from the ringdown signal

12. The method of claim 9 wherein f and Q are determine from the frequency sweep signal

13. The method of claim 1 applied recursively to determine f and Q as a function of time

14. The method of claim 7 where the starting frequency is determined using the method of claim 6.

15. The methods of claim 9 wherein the method of claim 8 is used as an estimate of the resonance parameters for selecting the excitation frequencies.

16. The methods of claim 10 wherein the method of claim 8 is used as an estimate of the resonance parameters for selecting the excitation frequencies.

17. The methods of claim 11 wherein the method of claim 8 is used as an estimate of the resonance parameters for selecting the excitation frequencies.

18. The method of claim 7 where the signal generator excitation frequencies are algorithmically selected to minimize the required number of frequencies.

19. The method of claim 15 wherein the signal generator excitation confirms or refutes peaks in the fast fourier transform as the oscillator resonance.