Intelligent Positioner Diagnostics for Accurate Pneumatic Actuator Friction
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Solution Overview
Problem
Current diagnostics methods for intelligent positioners of pneumatic actuators are limited by the inability to discriminate between forces required to overcome friction and those needed for acceleration, and are affected by phase delays and pressure drops in pipes, leading to inaccurate friction analysis.
Innovation Solution
A method for implementing 'on-service' diagnostics that discriminates valid pressure difference readings by considering low flow rates and low actuator speeds, allowing for accurate force measurements and friction analysis without additional instrumentation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure difference readings are taken during actuator operation, then diagnostic data can be obtained, but the readings are contaminated by acceleration forces and fluid forces making friction analysis inaccurate
Solution Approach 1:
The method segments the diagnostic process by identifying and separating valid measurement conditions from invalid ones. It divides the continuous operation into discrete valid intervals where friction can be accurately measured, based on specific criteria (low flow rate, low speed, low acceleration). This segmentation allows the system to extract clean friction data from the contaminated operational signal.
Solution Approach 2:
The method performs preliminary filtering of measurement data by establishing validity criteria before analysis. It pre-identifies which measurement intervals are suitable for friction analysis by checking conditions (flow rate below threshold, speed below threshold, acceleration below threshold) before using the data, thus preventing contaminated data from affecting the diagnostic results.
2Measurement precision
If additional sensors or instrumentation are added to improve measurement accuracy, then friction analysis precision improves, but device complexity and cost increase
Solution Approach 1:
The method makes the existing positioner device self-diagnostic by using its own built-in sensors (pressure, position, flow rate) to evaluate the validity of its own measurements. The system autonomously determines when its measurements are reliable without needing external validation equipment, thus achieving improved accuracy without adding instrumentation complexity.
Solution Approach 2:
The method enables the existing positioner to perform multiple functions: normal positioning control and self-diagnostic friction analysis. By making the positioner multi-functional, the system achieves enhanced diagnostic capability without adding dedicated instrumentation, as the same sensors serve both control and diagnostic purposes.
3Speed
If pressure readings are taken in the positioner, then real-time data is available, but pressure drops in pipes cause the readings to not reflect actual actuator chamber pressures
Solution Approach 1:
The method dynamically evaluates the validity of pressure readings based on real-time operating conditions. Instead of using a fixed correction or assumption, the system adaptively determines which pressure readings are valid by checking dynamic conditions (low flow rate, low speed). This dynamic approach allows the system to use rapid pressure readings when valid and ignore them when compromised by pipe pressure drops.
Data Source
Figure 1~2
AI summary
Method for implementing an on-service diagnostics of an intelligent positioner (3) for pneumatic actuators (2), the method being provided with the following steps: a) identifying a sampling where a pressure difference (ΔPp) measured in the positioner (3) is substantially equal to a pressure difference (ΔPa) in the actuator (2) and then it assumes the sampling as valid under conditions of: - low flow rate of the working fluid; - low, constant or with negligible or almost zero acceleration speed of the actuator and the working fluid; - reading received at a sufficiently time distance from accelerations and/or high speed and/or high flow rate, b) correctly storing the pressure difference (ΔPp) measured in the positioner, c) processing the data received to report alarms/warnings and/or order decisions.