Collect, Analyze, Decide, and Act on Critical Measurements

by | Apr 9, 2009 | Measurement Instrumentation

Jim Cahill

Chief Blogger, Editor

Emerson’s Bill Zhou is in town this week, escaping the cold north of Minnesota. You may recall Bill, from his Emerson Exchange plugged impulse line video demonstration. Actually, his purpose was not to see the Austin wildflowers in full bloom, but to work with the DeltaV product application specialists to share some of the capabilities in the Rosemount 3051S transmitter and what information it shares with systems like the DeltaV system. The team is also creating a video for us to add into the DeltaV YouTube site and other locations.

I’ve shared some of the statistical process monitoring (SPM) technology and how it helps spot abnormal situations by being closer to the process than the automation system is. These 3051S devices measure pressure, differential pressure (DP) level, and DP flow. They sample the process variable (PV) at 22 times per second compared with a typical 1-2 times per second from the automation system level.

Statistical Process Monitoring Model
It’s this higher frequency data collection and applied statistical analysis to measure process variability that provides operations personnel more information about what’s really happening in the process. Changes in this process variability can help uncover process- and equipment-related problems. Bill recommends using this high-resolution process variability as seen by the transmitters and following the four-step SPM model: Collect, Analyze, Decide, and Act.

The Collect step is about gathering as much process information as possible by trending the pressure and process variability inside the data historian application. With this collected information, step 2 is to Analyze the information and initially to establish a baseline. In subsequent times, process variability reductions, calculated by SPM can indicate process conditions like plugged impulse lines.

Step 3, the Decide step, determines the appropriate threshold limits to warn operators or maintenance personnel when actions need to be taken. The AMS Device Manager is used to set alerts based upon a change in process variability. Bill set a threshold of 30% process variability change in his demo example.

Step 4, the Act step, creates a notification for action once the threshold is crossed in the form of an alert on the DeltaV operator or maintenance station. Typically, specific operating procedures would be created for the critical measurement alerts. The actions might include checking the impulse line or other process/equipment condition based upon what the transmitter is measuring. These alerts are included with the historian process history to help achieve a wider view of what’s happening in the process and identify future abnormal situations.

I’ll update the post and embed the video once it has been produced and uploaded to YouTube.

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