Sean Heine, Account Manager at Emerson Impact Partner Novaspect, and Kurtis Jensen, Global Manager at Emerson, recently published an article in the May 2020 issue of Flow Control magazine describing a successful implementation of WirelessHart for mobile carts in an end user’s product lab. A summary of that article appears below.
Wireless Monitoring to Wireless Control
Many automation professionals are using wireless instrumentation for monitoring applications, but few have employed the technology for real-time control. This paradigm is changing due to improved wireless gateway communications, along with specific wireless control algorithms, enabling end users to realize wireless control benefits.
The article described an application at a large chemical company which recently employed WirelessHART control in its product development lab area. The lab was comprised of numerous small batch reactors processing a variety of products. Since the raw materials varied significantly from reactor to reactor and from day to day, the lab utilized a collection of mobile raw material carts to charge materials. The authors described the problem:
Each cart consisted of three Coriolis flowmeters, three control valves with digital valve positioners, and three local flow controllers. The charges were set up by the operators, who manually entered the charge amounts and continuously monitored the flows to ensure the flow rate and total charge values were correct. There were several significant limitations to this arrangement:
The project team studied the problem and realized the potential for significant improvement if they could control the mobile cart charges with the existing automation system. Such an arrangement would improve flow control, allow the operator to monitor simultaneous charges from a single remote location, provide a means to historize the data, and allow the batch system to control the process and capture the associated charge data. The project would yield even greater savings if the existing flowmeters and control valves could be re-used.
Figure 1. The cylindrical devices shown here — Emerson THUM wireless modules — are installed on Coriolis flowmeters.
Wireless Control is the Solution
After evaluating their options, the facility decided to pursue a wireless control strategy. Rather than replacing the instruments, they installed THUM wireless modules on each flow transmitter (Figure 1) and digital valve positioner (Figure 2).
Figure 2: THUM wireless module installed on a digital valve positioner.
A THUM module allows a wired transmitter to communicate over a WirelessHART network by transmitting the 4-20mA process variable signal to the automation system. It also allows a valve positioner to be controlled via WirelessHART by placing the positioner in digital mode and commanding the valve position via HART communication.
To facilitate communications with the cart instrumentation, the plant installed a redundant WirelessHART gateway and tied it into their automation system network via a hardwired digital data link (Figure 3).
Figure 3: A WirelessHART system is controlled by a network manager, ensuring deterministic update of the process measurement.
Once the data links were established between the field instrumentation and the automation system, the flow control loops were programmed into the system using PIDPlus control blocks (Figure 4). The PIDPlus algorithm is specifically developed to allow the controller to continue to operate consistently and reliably despite variable update times. Once those modules were created, the flow loops were added to the automation system graphics and the material charges were incorporated into the batch program.
Figure 4. Wireless communications enable real-time control of mobile cart operations.
The authors described the project outcome:
The improvements were dramatic and immediate and have proven to be valuable over both the short and long term.
The flow control data for all of the reactor flow loops is now available on any operator station, and charge flows for numerous reactors can be continuously monitored and alarmed. In addition, all the flow data can now be trended and stored in the historian for future reference.
The charges can be programmed into the batch system, with the resulting charge values written to the batch record upon completion of the charge. What’s more, none of the existing Coriolis meters, control valves or digital positioners required replacement—resulting in significant savings.
Recent improvements in wireless gateways, wireless mesh networks, and control algorithms have taken WirelessHART real-time control from the world of research studies and theory into operating plants. While there are technical considerations that must be evaluated, the savings and value offered by wireless control makes the technology worth considering for many process automation applications.
Figures all courtesy of Emerson
About the Authors
Sean Heine is an account manager for Novaspect. He is responsible for Emerson’s Final Control portfolio. Heine has been working in various capacities at Novaspect for the last five years, including six months at Emerson’s Fisher facility in Marshalltown, Iowa.
Kurtis Jensen is a global manager for Emerson's Fisher instrumentation. He is responsible for product development, serving as an advocate and promoter of innovative technologies that benefits end users. Jensen has over 35 years’ experience in field service, control systems, SCADA, RTUs, communications, cybersecurity wireless technologies and field instrumentation.
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