Positioner Pressure Calibration for Stiction-Prone SIS Actuators
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Emergency shutdown valves (ESVs) and other components of Safety Instrumented Systems (SISs) in industries like petroleum face issues with loose connections, significant lost motion, high seal friction, and stick-slip dynamics, leading to poor throttling control and inaccurate calibration during partial stroke testing due to high gain characteristics.
Innovation Solution
A method and apparatus using pressure control techniques to calibrate positioners by controlling pressure within or supplied to actuators, rather than travel, to determine biases and perform tests, thereby addressing inconsistencies from lost motion and friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional travel control methods are used to calibrate positioners, then the calibration process is simple to implement, but the calibration accuracy deteriorates due to lost motion, friction, and stick-slip dynamics
Solution Approach 1:
The patent replaces mechanical travel control with pneumatic pressure control. Instead of controlling the valve stem position directly through mechanical means, the system controls the pneumatic pressure supplied to the actuator. This substitution eliminates the problems of lost motion, friction, and stick-slip dynamics that plague mechanical travel control, thereby significantly improving calibration accuracy.
Solution Approach 2:
The patent introduces pressure control as an intermediary between the control system and the valve position. Rather than directly controlling travel, the system uses pressure as a mediator that indirectly controls valve position through the actuator. This intermediary approach allows for smoother, more precise control without the mechanical imperfections of direct travel control.
2Measurement precision
If pressure control techniques are used to calibrate positioners, then calibration accuracy improves by eliminating lost motion and friction effects, but the control system complexity increases
Solution Approach 1:
The patent replaces mechanical travel control with pneumatic pressure control. Instead of controlling the valve stem position directly through mechanical means, the system controls the pneumatic pressure supplied to the actuator. This substitution eliminates the problems of lost motion, friction, and stick-slip dynamics that plague mechanical travel control, thereby significantly improving calibration accuracy.
3Reliability
If I/P biases are not properly calibrated in high gain SIS actuators, then the system operation is simple, but the test results become meaningless due to dramatic impact of small pressure changes
Solution Approach 1:
The patent implements feedback control where the actual pressure supplied to the actuator is measured and fed back to the control system. This feedback loop allows the system to detect and correct any deviations from the desired pressure, ensuring that small pressure changes are precisely controlled. The feedback mechanism is crucial for maintaining test validity in high gain systems where even minor pressure variations can significantly impact results.
Data Source
Figure 1
Figure 2A~2b
Figure 2C
AI summary
A method of calibrating a positioner includes determining a pressure value corresponding to a particular state of an actuator, wherein the actuator is controlled by the positioner, and controlling a pressure within the actuator according to a set point pressure, wherein the set point pressure is based on the pressure value such that the particular state of the actuator is maintained. The method further includes receiving a measured value indicating an actual pressure within the actuator, and determining a bias of the positioner based on the measured value and the set point pressure.