Wireless versus Wired Process Control Performance Analysis

I just saw a tweet about WirelessHART being used in control applications. I followed the link to a ControlGlobal.com article by Emerson’s Terry Blevins and the University of Texas’ Frank Seibert. The article, WirelessHART Successfully Handles Control describes how these devices were applied and the performance evaluated at the Separations Research Program (SRP) at the University of Texas at Austin.

These pilot plant operations are unique in that they require:

…significant equipment modifications and additions. In these activities, process setup and decommissioning take about three times longer than the actual runs. So, decreasing setup time and pilot plant downtime are a high priority. Use of wireless transmitters provides a new degree of flexibility in reconfiguring the process without installing or relocating transmitter wiring.

To test the suitability of IEC 62591 WirelessHART devices in control applications, the wireless transmitters were:

…installed in parallel with wired transmitters for a few critical loops on an absorber and stripper process.

The operators could switch control between the wired and wireless transmitters on these control loops and see the impact on the process. To evaluate the performance more scientifically, Terry worked with the UT team to add metrics:

…to the control module to calculate the integral of absolute error (IAE) while on automatic control. Also, the number of new measurement values used in control and the duration of control were automatically captured to allow comparison of wired versus wireless control performance.

In an earlier blog post, I pointed to a whitepaper, which shares the changes that were required for the DeltaV PID algorithm to address the differences between wired transmitters periodic-based communications and wireless devices exception-based communications.

From the extensive testing and accumulated metrics, the team concluded:

…the combination of WirelessHART transmitters with PID modifications for wireless communication performed as reliably as the standard SRP hard-wired transmitters using traditional PID.

You’ll want to read the article for more on the application, the installation, and the testing conducted. There just might be an application in your plant to control your process with wireless devices.

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