Positioner Shift Magnitude Calculation for Valve Control Stability
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Solution Overview
Problem
Conventional positioners for controlling valve openings face challenges with controllability due to non-linear characteristics of electropneumatic converters and pilot relays, leading to instability and loss of settling performance, especially when noise is present in differential pressure feedback.
Innovation Solution
A positioner that includes a shift magnitude calculating portion to estimate the change in output air pressure prior to actual changes, using the equation d=Po−(K·Pn−F), and incorporates this shift magnitude into the control signal to improve responsiveness without compromising settling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If differential pressure feedback is used to improve responsiveness, then control speed increases, but control stability deteriorates due to noise amplification
Solution Approach 1:
The shift magnitude calculating portion performs preliminary calculation of the shift magnitude d = Po - (K×Pn - F) based on current input air pressure Pn and output air pressure Po, before actual pressure changes occur. This preliminary action allows the control calculating portion to anticipate and compensate for pilot relay behavior, improving responsiveness without amplifying noise from differential pressure feedback.
2Manufacturing precision
If feedback control is implemented to improve controllability, then valve positioning accuracy improves, but system complexity increases due to non-linear characteristics
Solution Approach 1:
The invention introduces a shift magnitude parameter d = Po - (K×Pn - F) that transforms the complex non-linear pilot relay characteristics into a compensatable parameter. By calculating and applying this shift magnitude in the control output, the system maintains accurate valve positioning while simplifying the control strategy, as the shift magnitude can be computed from readily available pressure measurements without requiring complex non-linear modeling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances controllability by anticipating changes in output air pressure, reducing instability and maintaining control stability even in the presence of noise, thereby improving responsiveness without affecting settling performance.
Implementation Method 1
an electropneumatic converter that converts the control signal from the control calculating portion into air pressure
Implementation Method 2
a pilot relay that uses, as an input air pressure, the air pressure converted by the electropneumatic converter, to amplify the input air pressure to produce an output air pressure
Data Source
AI summary
A positioner includes a shift magnitude calculating portion that calculates a shift magnitude from the equilibrium state of a pilot relay, from an input air pressure that is inputted into the pilot relay and an output air pressure that is outputted from the pilot relay. A control calculating portion determines a control signal from an actual opening signal, an opening setting value, and the shift magnitude from the equilibrium state of the pilot relay that is calculated by the shift magnitude calculating portion, and outputs it to the electropneumatic converter.