View, Trend, and Configure Advanced Pressure Diagnostics

20121009-105608.jpgEmerson’s Tom Wallace shared some new templates available in the DeltaV control system version 11 or newer to better understand and access advanced diagnostics from smart pressure devices. His abstract [hyperlink added to article]:

Advanced pressure diagnostics use statistical process monitoring to characterize process variation and detect abnormal conditions such as plugged impulse lines, furnace flame instability, or distillation column flooding. New DeltaV Diagnostics Module Templates, including control modules, operator faceplates, and process history view ease configuration and use of advanced diagnostics. This topic is scheduled to be a special editorial focus for the Sept / Oct issue of InTech magazine.

Tom opened with familiar challenges–getting early warning, keeping expertise, and finding time for training. Statistical process monitoring (SPM) in pressure transmitters can spot process noise before the control system sees it, since it samples at 22 times / second instead of 1 or 2.

This process noise can spot conditions such as plugged linkes, agitation loss, entrained air, process leakage, flame flicker, cavitation, and column flooding. The transmitter filters out the low frequency noise to statistically analyze the high frequency noise. The standard deviation can either increase or decrease depending on the process condition that occurs. This means you have to know about what’s going to interpret these statistical diagnostics.

Tom noted that the transmitter excels at the data collection and the control system is better at displaying the condition, historizing the data, fingerprinting the abnormal conditions in the process, and performing multi-loop SPM and optimization.

Many steps were required to setup these SPM diagnostics for the operators. To address this hurdle, pre-configured control module templates process history view charts, operator faceplates, and user help were created for the DeltaV system. These pre-engineered components were created for both Foundation fieldbus and HART devices.

Also, alarm flooding was a consideration so an alarm enable/disable is included to turn on or off all SPM alarms. The logic is available in CALC blocks and is fully accessible and commented to allow changes based on specific applications. By default, all the SPM alarms are disabled to allow users to enable based upon the specifics of their process.

Tom showed an operator faceplate showing the standard deviation alarm limits. It looked very similar to the existing process loop faceplates. To apply, create an operator reference book with what normal (the process signature) looks like. Capture the abnormal condition and when it was first detected by the SPM diagnostics. Capture corrective actions and process signature of corrective actions, and document most effective corrective actions.

For plant engineers, expect the unexpected, experiment to see what insights are revealed. Start with standard templates, then modified as required to fit your process.

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