Valve Position Control Diagnostics Using Approximation Signals
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Solution Overview
Problem
Existing valve actuators in process plants face challenges in diagnosing faults due to limited availability of process signals locally, which complicates the identification of error causes both within and outside the valve actuator.
Innovation Solution
A position controller for valve actuators is designed to generate a manipulated variable based on a command signal and an actual position signal, and it calculates an approximation signal using a configurable controller model related to the process controller. This allows the valve actuator to perform diagnostic routines that consider both local and higher-level process signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If diagnostic routines are performed using only local process signals in the valve actuator, then the device complexity is reduced, but the measurement precision and fault identification accuracy deteriorate due to limited signal availability
Solution Approach 1:
A signal processing unit is introduced as an intermediary component in the valve actuator that receives process signals from the process controller and transforms them into approximation signals through inverse control calculations. This intermediary enables the valve actuator to access higher-level process information without direct connection to the process controller, resolving the contradiction between limited local signals and accurate fault diagnosis.
Solution Approach 2:
The diagnostic system is segmented into multiple functional units: a signal processing unit for transforming process signals into approximation signals, and a diagnostic routine execution unit for analyzing faults. This segmentation allows each unit to specialize in specific tasks, improving overall diagnostic accuracy while maintaining modular device complexity.
2Measurement precision
If the valve actuator accesses higher-level process signals directly from the process controller, then the fault identification accuracy improves, but the device complexity and communication requirements increase
Solution Approach 1:
The signal processing unit acts as a self-contained intermediary that performs inverse control calculations locally using only the process control signal already received from the process controller. This eliminates the need for additional communication interfaces or direct access to higher-level process signals, while still enabling accurate fault identification through generated approximation signals.
Solution Approach 2:
The signal processing unit creates local copies (approximation signals) of higher-level process signals through mathematical transformation of the received process control signal. These copied signals replicate the information content needed for diagnosis without requiring physical access to the original higher-level signals, reducing communication complexity.
3Reliability
If inverse control calculations are performed to generate approximation signals, then the diagnostic capability improves, but the computational load and processing time increase
Solution Approach 1:
The inverse control model is pre-configured in the signal processing unit with predetermined calculation parameters and algorithms. This preliminary preparation allows the unit to perform rapid inverse control calculations during operation by simply applying pre-established mathematical relationships to the received process control signal, minimizing real-time computational load and processing time.
Data Source
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AI summary
In a position closed-loop controller (31) for a valve control device (1) of a process engineering plant (100), comprising a first signal input (11) for a pilot signal, such as a process control signal (pg) from a process closed-loop controller (120) of the process engineering plant (100), a second signal input for a position actual signal (i) with regard to a control valve (35), wherein the position control-loop controller (31) is designed to generate a more particularly pneumatic control variable (g) for an actuator (33) to actuate the control valve on the basis of the pilot signal and the position actual signal (i) and comprises a more particularly pneumatic control output for the control variable (g). According to the invention, the position closed-loop controller (31) is configured to calculate an approximation signal (ap), by means of a configurable closed-loop controller model based on a particular closed-loop controller, more particularly the process closed-loop controller (120), proceeding from the pilot signal, wherein the closed-loop controller model is configured such that a signal generated by the particular closed-loop controller proceeding from the approximation signal (ap) corresponds to the pilot signal.