US 9,429,938 B2Granted

Method and apparatus for qualifying performance of a conventional control valve

AssigneeYokogawa Electric Corporation

InventorsSankar Selvaraj, Lakshmi Kiran Kanchi, Ching Hua Joseph Lee

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Abstract

A method of qualifying performance of a conventional control valve in a process plant, the valve being controlled by a controller, the method comprising a processor obtaining data samples from a database stored on a server of the process plant, each data sample comprising a process variable, a set-point, and a manipulated variable; the processor computing a non-linearity index from the data samples and determining if the non-linearity index is greater than a threshold value; if the non-linearity index is greater than the threshold value, the processor charting a plot of the process variable against the manipulated variable and determining if the plot has an elliptical or rectangular fit; and if the plot has an elliptical fit, the processor determining if a percentage of the total number of data samples lying within a theoretical ellipse encompassed within the elliptical fit is less than or equal to a preset percentage.

Claims12

Dependent claims

A method of qualifying performance of a conventional control valve that does not have a self-provided feedback mechanism that allows a user to qualify valve performance in a process plant, the valve being controlled by a controller, the method comprising:

sensing, with a flow rate sensor, a flow rate at a location in the process plant, the flow rate being controlled by the conventional control valve;
storing in a database of a server of the process plant the flow rate sensed by the sensor, a set-point being a pre-determined desired value for the flow rate, and a manipulated variable being a value sent from the controller to the conventional control valve for adjusting the flow rate to reach the set-point;
a processor obtaining data samples from the database stored on the server of the process plant, each data sample comprising the flow rate sensed by the flow rate sensor, the set-point, and the manipulated variable;
the processor computing a non-linearity index from the data samples and determining if the non-linearity index is greater than a threshold value;
if the non-linearity index is greater than the threshold value the processor charting a plot of the process variable against the manipulated variable and determining if the plot has an elliptical or rectangular fit;
if the plot has an elliptical fit, the processor determining if a percentage of the total number of data samples lying within a theoretical ellipse encompassed within the elliptical fit is less than or equal to a preset percentage;
if the plot has an elliptical or rectangular fit and the percentage is less than or equal to the preset percentage, the processor computing a model fitness stiction index of the plot relative to a standard valve stiction model, and determining if the model fitness stiction index is greater than a pre-set value known to arise due to valve stiction;
the processor determining whether valve stiction is associated with the conventional control valve based on whether the model fitness stiction index is greater than the pre-set value;
and
adjusting, using the controller, the flow rate at the location in the process plant to reach the set-point by sending the value corresponding to the manipulated variable to the conventional control valve.

7 more elements

An apparatus for qualifying performance of a conventional control valve in a process plant, the valve being controlled by a controller, the apparatus comprising:

a conventional control valve that does not have a self-provided feedback mechanism that allows a user to qualify valve performance;
a sensor that senses flow rate at a location in the process plant, the flow rate being controlled by the conventional control valve;
a server that includes a database storing the flow rate sensed by the sensor, a set-point being a pre-determined desired value for the flow rate, and a manipulated variable being a value sent from the controller to the conventional control valve for adjusting the flow rate to reach the set-point;
the controller configured to adjust the flow rate at the location in the process plant to reach the set-point by sending the value corresponding to the manipulated variable to the conventional control valve;
and
a processor configured to obtain data samples from the database stored in the server of the process plant, wherein the processor comprises
a data preparation processor configured to obtain data samples from the database, each data sample comprising the flow rate sensed by the flow rate sensor, the set point and the manipulated variable, and
an analysis processor configured to compute a non-linearity index from the data samples, to determine if the non-linearity index is greater than a threshold value, to chart a plot of the process variable against the manipulated variable, to determine if the plot has an elliptical or rectangular fit, and to determine if a percentage of the total number of data samples lying within a theoretical ellipse encompassed within the elliptical fit is less than or equal to a preset percentage,
wherein the analysis processor is further configured to compute a model fitness stiction index of the plot relative to a standard valve stiction model and to determine if the model fitness stiction index is greater than a pre-set value known to arise due to valve stiction, and
wherein the analysis processor is further configured to determine whether valve stiction is associated with the conventional control valve based on whether the model fitness stiction index is greater than the pre-set value.

7 more elements

Dependencies are inferred from the claim text.