INTUNE+ Loop Optimization
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INTUNE Valve Diagnostics
About 30%* of unacceptable control loop performance in process industries is due to problems with control valves. Variability caused by control valves is difficult to regulate without proper diagnosis and treatment of the source.
Our INTUNE+ Valve Diagnostics plugin qualitatively detects and quantifies the size of valve stiction in both online and offline diagnostic modes and:
- Requires no additional hardware or instrumentation; uses information available in existing control systems, specifically process values, controller outputs, setpoints, and valve position (if available).
- Can perform analysis with or without valve position feedback signal.
- Analyzes the performance of valves in normal closed loop operation, and reports status in real time — no need for intrusive testing methods (online mode).
- Measures and detects in real time the gradual degradation of loop performance due to valve problems, aiding in predictive maintenance (online mode).
- Performs a similar analysis on data collected by any historian (offline mode).
- Enables users to visually evaluate the trend and data plot provided by the diagnostics tool through the Results display.
- Uses pattern recognition technology to provide both qualitative and quantitative stiction diagnostic results. These results are complemented by a measure that indicates confidence of the analysis with time stamp.
- Lets users save and report on valve status parameters and trends. Users can also plot data from current online diagnostic, offline diagnostic, or maximum stiction results.
- Configure diagnostics using a wizard tool or by entering the specifications line by line (advanced).
When valve position is not available for analysis, the faceplate of the Valve Diagnostic tool for Closed Loop Monitoring shows CO-PV plot and Stiction Index (a confidence level).
This faceplate combines an Ygraph of the controller CO-PV with control loop time-trended performance data.
The severity of stiction is quantified as a percent value.
This display also provides a qualitative determination, confidence level index, and the daily worse-case stiction data.
The Valve Diagnostics plugin saves the maximum stiction measurement, and allows users to reset the measurement when desired.
When valve position is available for analysis, the faceplate of the Valve Diagnostic tool for Closed Loop Monitoring shows MV-PV plot and valve position in Trends window.>
When the valve position is available to use in the analysis, a more accurate valve performance determination can be made.
Having the valve position signal (MV), the CO-PV graph changes to CO-MV and valve position is also shown in Trends window.
This sample web report shows control valve performance for multiple loops in a quantitative and qualitative format. This report can be used to monitor valve performance over time or to establish a baseline for evaluating subsequent improvements.
One of the important features of INTUNE is its ability to generate web reports from the results of the diagnostic tool. This web report uses the outputs of the Valve Diagnostic tool for a number of loops.
* Srinivas Karra and M. Nazmul Karim in "Oscillatory Control Loops: The Lost Economic Benefits. Can Anything Be Done?" (Process Control & Optimization, 2009 AIChE Spring Meeting).