Plant parameter detection by monitoring of power spectral densities

Claim 1

A method for determining a current state of a process variable output signal and whether the output signal is within acceptable limits, the method comprising the steps of: (a) establishing reference comparison data for said process variable by sampling a reference output signal over a first period of time when said plant is operating at steady state, each sampled reference output signal further subjected to a first normalization procedure to convert each sampled signal to a zero mean basis; (b) processing said sampled output signal to derive reference spectral data for said process variable, said reference spectral data manifesting a normalized energy content for each of a plurality of frequency components of said sampled output signal, each reference spectral data value subjected to a second normalization procedure, wherein each spectral data value is divided by a sample time related value, a sample time being a window of time during which an output signal is sampled in preparation for deriving spectral data values therefor; (c) storing said reference spectral data; (d) establishing current operational data for said process variable by sampling a current output signal for said process variable over a second period of time when said plant is in operation, each sampled current output signal further subjected to a first normalization procedure to convert each sampled signal to a zero mean basis; (e) processing said sampled current output signal to derive current spectral data therefrom, said current spectral data manifesting a normalized energy content of each of a plurality of frequency components of said sampled current output signal, each current spectral data value subjected to a second normalization procedure, wherein each spectral data value is divided by a sample time related value, a sample time being a window of time during which an output signal is sampled in preparation for deriving spectral data values therefor; and (f) for each of a plurality of common frequency components of said reference spectral data and current spectral data, comparing normalized energy contents therefor and issuing a signal if said comparing indicates that an energy content threshold of any frequency component of said current spectral data exceeds an energy content of a common frequency component of said reference spectral data.

Claim 2

A method for determining a current state of a process variable output signal and whether the output signal is within acceptable limits, the method comprising the steps of: (a) establishing reference comparison data for said process variable by sampling a reference output signal over a first period of time when said plant is operating at steady state, each sampled reference output signal further subjected to a first normalization procedure to convert each sampled signal to a zero mean basis; (b) processing said sampled output signal to derive reference spectral data for said process variable, said reference spectral data manifesting a normalized energy content for each of a plurality of frequency components of said sampled output signal, each reference spectral data value subjected to a second normalization procedure, wherein each spectral data value is divided by a sample time related value, a sample time being a window of time during which an output signal is sampled in preparation for deriving spectral data values therefor; (c) storing said reference spectral data; (d) establishing current operational data for said process variable by sampling a current output signal for said process variable over a second period of time when said plant is in operation, each sampled current output signal further subjected to a first normalization procedure to convert each sampled signal to a zero mean basis; (e) processing said sampled current output signal to derive current spectral data therefrom, said current spectral data manifesting a normalized energy content of each of a plurality of frequency components of said sampled current output signal, each current spectral data value subjected to a second normalization procedure, wherein each spectral data value is divided by a sample time related value, a sample time being a window of time during which an output signal is sampled in preparation for deriving spectral data values therefor; and (f) for each of a plurality of common frequency components of said reference spectral data and current spectral data, comparing normalized energy contents therefor and issuing a signal if said comparing indicates that an energy content threshold of any frequency component of said current spectral data exceeds an energy content of a common frequency component of said reference spectral data.