Process variable transmitter with diagnostics

• US 20060036404A1
• Filed: 08/17/2005
• Published: 02/16/2006
• Est. Priority Date: 03/28/1996
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Miller, John P., Eryurek, Evren, Lamothe, Ross C., Wiklund, David E., Kavaklioglu, Kadir
• Granted Patent: US 7,949,495 B2
• Time in Patent Office: Days
• US Class Current: 702/183
• CPC Class Codes: G01F 1/363 with electrical or electro-mechanical indication G01F1/37 and G01F1/38 take precedence
• CPC Class Codes: G01F 1/50 Correcting or compensating means
• CPC Class Codes: G01F 25/10 of flowmeters
• CPC Class Codes: G05B 13/0275 using fuzzy logic only
• CPC Class Codes: G05B 21/02 electric
• CPC Class Codes: G05B 23/0229 knowledge based, e.g. expert systems; genetic algorithms
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

A process variable transmitter with diagnostics based on power spectral density (PSD) analysis of a process variable sensor signal is provided. In one embodiment, the process variable transmitter is a pressure transmitter and the diagnostics are used to diagnose impulse line obstruction or impending obstruction. Other diagnostics are also useful such as diagnosing primary element degradation. The sensor signal is digitized and the digitized signal is transferred into the frequency domain. The power of the frequencies on the sensor signal is examined to provide the enhanced diagnostics. In one aspect diagnostics are generated directly with the sensor PSD data. In another aspect, the PSD analysis is used to tune a filter in order to enhance traditional diagnostic algorithms.

Claims

1. A process variable transmitter for coupling to a process and providing an indication of a variable of the process over a communication bus, the process variable transmitter comprising:

a process variable sensor coupleable to the process to provide an analog indication of the variable;

an analog-to-digital converter coupled to the process variable sensor and providing digital information indicative of the analog indication provided by the sensor; and

output circuitry configured to provide an output related to the process variable;

a microprocessor system coupled to the analog-to-digital converter and configured to calculate power spectral density of the digital information and responsively generate diagnostic information based on the power spectral density.

2. The transmitter of claim 1, wherein the transmitter is a pressure transmitter coupleable to the process via a plurality of impulse lines.

3. The transmitter of claim 2, wherein the diagnostics are indicative of a condition of the impulse lines.

4. The transmitter of claim 3, wherein the diagnostics are indicative of partial plugging of at least one impulse line.

5. The transmitter of claim 4, wherein the diagnostics indicate a time when the impulse lines will become completely plugged.

6. The transmitter of claim 1, wherein the analog-to-digital converter provides the digital information as a plurality of discrete digitized conversion values.

7. The transmitter of claim 6, wherein the discrete digitized values are provided at a frequency of about 22 times per second.

8. The transmitter of claim 1, wherein the digital information includes digital bitstream data.

9. The transmitter of claim 8, wherein the bitstream data is provided at a frequency in excess of about 55 kHz.

10. The transmitter of claim 9, wherein the digital information is transferred to the frequency domain using a Fast Fourier Transform (FFT).

11. The transmitter of claim 10, wherein the power spectral density is computed using a Hanning window size of approximately 65536.

12. The transmitter of claim 11, wherein the diagnostic information is based on an integral of the power of frequencies ranging from about 1 to about 10 Hz.

13. The transmitter of claim 11, wherein the diagnostic information is based on an integral of the power of frequencies ranging from about 10 to about 30 Hz.

14. The transmitter of claim 11, wherein the diagnostic information is based on an integral of the power of frequencies ranging from about 10 to about 40 Hz.

15. The transmitter of claim 11, wherein the diagnostic information is based on an integral of the power of frequencies ranging from about 30 to about 40 Hz.

16. The transmitter of claim 1, wherein the digital information is transferred into the frequency domain using wavelet analysis.

17. The transmitter of claim 1, wherein the diagnostic information is generated based on a comparison of power spectral density information Fi with baseline power spectral density information Fi.

18. The transmitter of claim 17, wherein the comparison includes comparing the deviation in the sum of the magnitudes over selected frequencies.

19. The transmitter of claim 17, wherein the comparison includes comparing the standard deviation of the magnitudes over selected frequencies.

20. The transmitter of claim 17, wherein the baseline power spectral density is obtained during a training session.

21. The transmitter of claim 1, wherein the diagnostic information includes an indication of a fault.

22. The transmitter of claim 21, wherein the fault indication is a local fault indication.

23. The transmitter of claim 21, wherein the fault indication is transmitted over the communication buss.

24. The transmitter of claim 21, wherein the fault indication predicts a future event.

25. A method of predictively diagnosing a process variable transmitter having an analog-to-digital converter coupled to a process variable sensor that is coupled to a process, the method comprising:

obtaining a plurality of digital data from the analog-to-digital converter;

calculating power spectral density of the plurality of digital data;

comparing the calculated power spectral density with baseline power spectral density;

generating a predictive diagnostic output based upon the comparison.

26. The method of claim 25, wherein the plurality of digital data include a plurality of digitized conversions.

27. The method of claim 25, wherein the plurality of digital data includes digital bitstream data.

28. The method of claim 25, wherein the diagnostic output is indicative of a condition of at least one impulse line.

29. A process variable transmitter for coupling to a process and providing an indication of a variable of the process over a communication buss, the process variable transmitter comprising:

a process variable sensor coupleable to the process to provide an analog indication of a variable of the process;

an analog-to-digital converter coupled to the process variable sensor and providing digital information indicative of the analog indication provided by the sensor; and

microprocessor means for generating a process value and for generating a diagnostic output using power spectral density analysis.

30. A method of configuring a digital filter in a process variable transmitter, the method comprising:

a process variable sensor coupleable to the process to provide an analog indication of a variable of the process;

a analog-to-digital converter coupled to the process variable sensor and providing digital information indicative of the analog indication provided by the sensor;

a microprocessor system coupled to the analog-to-digital converter, The microprocessor system providing digital filtering of the analog-to-digital converter using configurable filter characteristics; and

wherein the configurable filter characteristics are chosen based on a power spectral density analysis performed during a training session.

31. The method of claim 30, wherein the filtered digital information is used to provide a process variable output.

32. The method of claim 30, wherein the filtered digital information is used to provide a diagnostic output.