Positioner Model Diagnosis for Pneumatic Control Valve Degradation
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Solution Overview
Problem
Pneumatic control valves in power plants require effective diagnostic methods to prevent abnormal states and maintain optimal operation, as existing methods are inadequate for real-time monitoring and prediction of valve state changes.
Innovation Solution
A method and apparatus using a positioner model to establish a relational expression for a pneumatic control valve, determining parameters that indicate its state, and comparing these parameters in real-time with reference values to diagnose abnormalities before they occur, thereby preventing shutdowns and improving operational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If regular maintenance and replacement of pneumatic control valve components are performed, then reliability is improved, but loss of time and productivity deteriorate due to shutdowns
Solution Approach 1:
The patent establishes a positioner model that performs preliminary diagnostic actions by continuously monitoring valve parameters and comparing them against normal operation baselines. This allows early detection of degradation trends before they cause valve failure, enabling maintenance to be scheduled at convenient times rather than being forced by unexpected failures or rigid preventive maintenance schedules.
Solution Approach 2:
The patent implements a feedback mechanism where valve diagnostic parameters are continuously measured, compared against the positioner model predictions, and used to update the assessment of valve health. This closed-loop feedback system enables real-time monitoring and early warning of degradation, allowing operators to take corrective action before the valve fails and causes shutdowns.
2Reliability
If valve diagnosing equipment is used to check abnormal states, then reliability is improved, but loss of time worsens due to power plant shutdowns required for diagnosis
Solution Approach 1:
The patent enables the pneumatic control valve to perform self-diagnosis through the positioner model, which continuously monitors its own operational parameters and compares them against expected behavior. This self-service capability eliminates the need for external diagnosing equipment and shutdowns to assess valve health, as the system can evaluate its own state in real-time during normal operation.
Solution Approach 2:
The patent maintains continuous diagnostic monitoring of the valve during normal power plant operation, eliminating the intermittent shutdowns required by traditional diagnostic methods. The positioner model continuously processes valve parameters and provides ongoing assessment of valve health, ensuring that diagnostic functions are performed without interrupting power generation.
3Measurement precision
If a positioner model is established with relational expressions and parameter adjustments, then measurement precision is improved for valve state detection, but device complexity increases
Solution Approach 1:
The patent uses parameter changes as the core mechanism of the positioner model, establishing relational expressions that connect valve input parameters (control pressure, positioner output) with output parameters (valve stem position). By adjusting and monitoring these parameters against baseline values, the system achieves precise measurement of valve state without requiring complex additional hardware, relying instead on sophisticated parameter analysis of existing sensor data.
Data Source
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AI summary
Provided is a method for diagnosing a pneumatic control valve by using a positioner model. The method may comprise the steps of: establishing a relational expression for outputting a valve stem displacement according to control pressure, the relational expression including parameters for the characteristics of a positioner, an actuator, and a valve; determining an initial parameter value by adjusting the values of the parameters until the difference between a measured 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; 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 comparing the initial parameter value and the diagnostic parameter value so as to determine whether the pneumatic control valve has an abnormality. Accordingly, it is possible to diagnose the state of the pneumatic control valve by estimating variations of the parameters in real time when the pneumatic control valve is operated and comparing the same with the values of the parameters in the normal state.