Electropneumatic Valve Control Using Backup Process Variables
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Solution Overview
Problem
Existing control methods for electropneumatic field devices in process plants, such as chemical and food processing plants, are inadequate in maintaining control during failures of the actuator position measurement, particularly in fast-changing or disturbed processes, leading to potential operational instability and significant economic losses.
Innovation Solution
A control method that utilizes alternative control variables, such as manifold pressure, actuator force, and process fluid-related variables, to determine the manipulated variable in emergency states, allowing continued control without direct actuator position measurement, using control algorithms like PID and incorporating redundant control strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If control is based on direct actuator position measurement, then control precision is improved, but reliability deteriorates when position sensor fails
Solution Approach 1:
The patent introduces intermediary variables (manifold pressure, actuator force, process fluid variables) that mediate between the control input and the actuator position. These intermediaries provide alternative measurement paths when the direct position sensor fails, allowing the control system to maintain operation through indirect inference of actuator position from other measurable quantities.
Solution Approach 2:
The patent changes the measurement parameters from direct position measurement to alternative parameters such as manifold pressure, actuator force, and process fluid variables. By monitoring and controlling these alternative parameters, the system can infer actuator position and maintain control functionality even when the direct position sensor becomes inoperative.
2Reliability
If redundant control variables and algorithms are implemented, then reliability is improved during failures, but device complexity increases
Solution Approach 1:
The patent makes the control system universal by enabling it to perform multiple functions: normal position-based control and emergency alternative-variable-based control. The same control device can operate in different modes depending on sensor availability, using manifold pressure, actuator force, or process fluid variables as substitutes for direct position measurement, thereby maintaining reliability without requiring entirely separate backup systems.
Solution Approach 2:
The patent implements preliminary action by pre-configuring the control device with multiple control algorithms and alternative measurement approaches. When normal operation fails, the system can immediately switch to pre-programmed alternative control strategies without requiring complex real-time decision-making or additional hardware, thus improving reliability while limiting complexity growth.
3Adaptability or versatility
If alternative control variables are used in emergency states, then adaptability is improved, but measurement precision may deteriorate
Solution Approach 1:
The patent applies dynamics by allowing the control system to adaptively switch between different measurement variables based on operational conditions. During normal operation, direct position measurement is used for high precision. During emergency states, the system dynamically transitions to alternative variables such as manifold pressure or actuator force, accepting reduced precision in exchange for continued adaptability and operational capability.
Data Source
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AI summary
In a control method for an electropneumatic field device, comprising a pneumatic actuator for actuating an actuator, such as a control valve, an electropneumatic transducer for generating a pneumatic control signal for the pneumatic actuator, and control and/or regulation electronics with an electrical setpoint input for a control variable to specify a setpoint, in particular from a control room, and an electrical output for a manipulated variable to control the electropneumatic transducer, the manipulated variable is determined in a predetermined operating state of the field device, such as an emergency control state, by a control algorithm based on the control variable and a controlled variable other than the actuator position actual measured value.