Diagnostic device for use in process control system

• US 20080103629A1
• Filed: 12/20/2007
• Published: 05/01/2008
• Est. Priority Date: 06/21/2005
• Status: Active Grant

• Current Assignee: ABB Research Ltd. (ABB Limited)
• Original Assignee: ABB Research Ltd. (ABB Limited)
• Inventors: Scholz, Wolfgang, Milanovic, Raiko, Andenna, Andrea
• Granted Patent: US 7,729,876 B2
• Time in Patent Office: Days
• US Class Current: 700/282
• CPC Class Codes: G05B 23/0237 based on parallel systems, e.g. comparing signals produced at the same time by same type systems and detect faulty ones by noticing differences among their responses
• CPC Class Codes: G05B 9/02 electric
• CPC Class Codes: Y10T 137/8326 Fluid pressure responsive indicator, recorder or alarm

Abstract

The diagnostic device for detecting a failure of a sensing means, which sensing means comprises a recording means for repeatedly recording pairs of two absolute pressure values, the absolute pressure values being related to absolute pressures in the first and the second impulse lines, respectively, a computation means for repeatedly computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure value, a comparison means for comparing correlation values to at least one correlation threshold value, and an output means for outputting a diagnostic output depending on the result of the comparison. It is possible to derive the absolute pressure values from one differential pressure measurement an one absolute pressure measurement.

Claims

1. A diagnostic device for detecting a failure of a sensing means, which sensing means comprises at least one of first and a second impulse lines, wherein the diagnostic device comprises

a recording means for repeatedly recording pairs of two absolute pressure values, the absolute pressure values being related to absolute pressures in the first and the second impulse lines, respectively,

a computation means for repeatedly computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure values,

a comparison means for comparing correlation values to at least one correlation threshold value, and

an output means for outputting a diagnostic output depending on the result of the comparison,

wherein the correlation values are compared to a lower correlation threshold value and to an upper correlation threshold value.

2. The diagnostic device according to claim 1, wherein the at least one correlation threshold value is derived from a statistical analysis of a number of correlation values obtained during a training phase.

3. The diagnostic device according to claim 2, wherein the statistical analysis comprises fitting a statistical distribution function to the correlation values recorded during the training phase.

4. The diagnostic device according to claim 1, wherein the computation means is designed for repeatedly computing, from a prescribable number of a first of the two absolute pressure values, a signal power value, and the comparison means is designed for comparing signal power values to at least one signal power threshold value, wherein signal power values are derived from a transform of the prescribable number of first pressure values into coefficients of a set of orthogonal functions.

5. The diagnostic device according to claim 4, wherein the transform is one of the group of Fourier transform and wavelet transform.

6. The diagnostic device according to claim 4, wherein the least one signal power threshold value is obtained from a number of signal power values obtained during a training phase.

7. The diagnostic device according to claim 1, wherein the diagnostic device comprises at least one sensing means

for measurement of an absolute pressure, and

for measurement of a differential pressure between the two impulse lines,

and wherein the two absolute pressure values are derived from measurements performed with the at least one sensing means.

8. A process control environment comprising a diagnostic device according to claim 1.

11. The diagnostic device according to claim 3, wherein the computation means is designed for repeatedly computing, from a prescribable number of a first of the two absolute pressure values, a signal power value, and the comparison means is designed for comparing signal power values to at least one signal power threshold value, wherein signal power values are derived from a transform of the prescribable number of first pressure values into coefficients of a set of orthogonal functions.

12. The diagnostic device according to claim 5, wherein the least one signal power threshold value is obtained from a number of signal power values obtained during a training phase.

13. The diagnostic device according to claim 6, wherein the diagnostic device comprises at least one sensing means

for measurement of an absolute pressure, and

for measurement of a differential pressure between the two impulse lines,

and wherein the two absolute pressure values are derived from measurements performed with the at least one sensing means.

14. A process control environment comprising a diagnostic device according to claim 7.

9. Diagnostic method for detecting a failure of a sensing means, which sensing means comprises at least one of first and a second impulse lines, the method comprising the steps of:

recording pairs of two absolute pressure values, the absolute pressure values being related to the absolute pressures in the first and a second impulse lines,

computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure values,

comparing correlation values to a lower correlation threshold value and to an upper correlation threshold value, and

outputting a diagnostic output depending on the result of the comparison.

10. Process control environment implementing a diagnostic method according to claim 9.