Method and apparatus for diagnosing pneumatic control valve by using positioner model

An apparatus for diagnosing a pneumatic control valve by using a positioner model, the pneumatic control valve including a controller for outputting a control pressure, a positioner for receiving the control pressure as an input and controlling a pressure supplied to an actuator, the actuator being for driving a valve based on the supplied pressure and the valve, the further comprising:

• a model generation unit for establishing a relational expression for outputting a valve stem displacement according to the control pressure, the relational expression including parameters for properties of the positioner, the actuator and the valve;
• an initial value determination unit for determining an initial parameter value by adjusting the values of the parameters until a difference between a measurement value for a normal operation of the pneumatic control valve and an output value obtained by the relational expression is smaller than a predetermined error limit;
• a diagnostic value determination unit for determining a diagnostic parameter value by adjusting the values of the parameters until the difference between a measured value for a diagnostic operation of the pneumatic control valve and an output value obtained by the relational expression is smaller than a predetermined error limit;
• and a diagnostic unit for determining whether the pneumatic control valve has an abnormality based on a comparison between the initial parameter value and the diagnostic parameter value, the positioner model comprising the relational expression and wherein the relational expression is an expression for outputting the valve stem displacement according to the control pressure, the relational expression including parameters for the properties of the positioner, the actuator, and the valve.

A storage medium readable by a computer for diagnosing a pneumatic control valve by using a positioner model, wherein the control valve includes a controller for outputting a control pressure, a positioner for receiving the control pressure as an input and controlling a pressure supplied to an actuator, the actuator for driving a valve based on the supplied pressure and the valve, the computer comprising a processor to perform:

• a command for establishing a relational expression for outputting a valve stem displacement according to the control pressure, the relational expression including parameters for properties of the positioner, the actuator and the valve;
• a command for determining an initial parameter value by adjusting the values of the parameters until a difference between a measurement value for a normal operation of the pneumatic control valve and an output value obtained by the relational expression is smaller than a predetermined error limit;
• a command for determining a diagnostic parameter value by adjusting the values of the parameters until the difference between a measured value for a diagnostic operation of the pneumatic control valve and an output value obtained by the relational expression is smaller than a predetermined error limit;
• and a command for determining whether the pneumatic control valve has an abnormality by comparing the initial parameter value and the diagnostic parameter value, the positioner model comprising the relational expression, the relational expression outputting the valve stem displacement according to the control pressure, the relational expression including parameters for the properties of the positioner, the actuator, and the valve.

A method comprising diagnosing a pneumatic control valve,

• the pneumatic control valve including a controller for outputting a control pressure, an actuator, a valve stem having a valve, a positioner for receiving the control pressure as an input from the controller and using said control pressure to provide a supplied pressure to said actuator, thereby enabling said actuator to displace said valve stem based on said supplied pressure,
• wherein, in response to said control pressure, said valve stem undergoes a displacement that depends on mechanical properties of said positioner, said actuator, and said valve,
• said mechanical properties being characterized by parameters,
• wherein diagnosing said pneumatic control valve comprises
• obtaining a measurement value for normal operation of said pneumatic control valve,
• adjusting values of the parameters for the properties of the positioner, the actuator, and the valve until a difference between said measurement value and a stem displacement that results from said values of said parameters is smaller than a predetermined error limit, thereby obtaining an initial-parameter value,
• adjusting the values of the parameters for the properties of the positioner, the actuator, and the valve until the difference between a measured value for a diagnostic operation of the pneumatic control valve and an output value obtained by the relational expression is smaller than a predetermined error limit, thereby determining a diagnostic parameter value, and
• comparing the initial parameter value and the diagnostic parameter value, and
• based on said comparison, determining that said pneumatic control valve has an abnormality.