Emerson’s Deji Chen and Mark Nixon have written a recently published book, WirelessHART™ – Real-Time Mesh Network for Industrial Automation. They teamed with University of Texas at Austin professor, Aloysius Mok to write a comprehensive work on this global wireless standard (IEC 62591) for the process industries. Professor Mok is known for his research in real-time embedded systems and was a past chairman of the Technical Committee on Real-Time Systems of the Institute of Electrical and Electronic Engineers (IEEE). Mark and Deji are key members of the DeltaV technology team.
I caught up with Deji to discuss the book. The first part of the book offers an overview of the WirelessHART standard. It describes the physical layer, data link layer, network and transport layers, application layer, and the architecture, security, and scheduling functions in a WirelessHART network.
If you are a technologist with one of the automation suppliers and seeking to add WirelessHART capabilities to your products, the book goes into depth to describe the inner workings of the WirelessHART technology. For example, in the physical layer, it highlights maximum bandwidth, communications packet length and its impact on reliability, channel hopping, and available diagnostics. There is similar detail with respect to the other layers in the communications stack.
Process automation professionals interested in how best to apply WirelessHART in their plant will find part III of the book, WirelessHART in Practice, to be beneficial. The HART Communication Foundation has operated a rigorous quality assurance program since 1995 for HART devices and now WirelessHART devices. The book describes some of the test and diagnostic tools used to assure compliance with the standard.
The deployment recommendations in chapter 14 offer guidance in the design of a wireless field network. One example is the number of WirelessHART field devices per access point. The number is a function of the average update rate. If all the devices update once per second, then 25 devices can be connected. If the average update rate is once per 10 seconds (or 6 per minute), then 250 devices can be wirelessly connected to the access point. Other formulas help process automation professionals calculate bandwidth consumed. The formulas are very conservative to help ensure successful installations.
The self-organizing nature of the WirelessHART communications standard means that detailed site surveys are not required. This is one of its inherent advantages over line-of-sight and point-to-point wireless network technologies. This self-organizing mesh also means that expanding the network is much easier than other approaches. As the authors note, the WirelessHART working group used a “keep-it-simple” philosophy in all phases from configuration to installation, support, and maintenance.
The authors give installation guidance such as deploying the gateway in the center of a network for a small wireless network. This gateway is what connects the WirelessHART network with the automation system or controller.
Looking forward, the authors describe the challenges of control over wireless networks and how PID control algorithms must change to accommodate the instances where lost communications may occur. Chapter 16 highlights the basis for these changes and how control systems such as the DeltaV system accommodate control over WirelessHART networks.
If you’d like a deeper understanding of this important global standard, you’ll find this book to be an important addition in your library of learning.
