The real-time communications capability of industrial Ethernet is a hot topic. It will be a key component of the Industrial Safety Network panel discussion being held on the first day of The Automation Conference 2014, in Chicago May 20-21. There, Joey Stubbs, PE, North American representative of the EtherCAT Technology Group, Gregory Richards, system engineer for Siemens Industry, Inc. and Sari Germanos, technology marketing manager of the Ethernet Powerlink Standardization Group, and others will be discussing time-critical safety applications.
In a paper published in the International Journal of Future Computer and Communication in April 2013, authors P. A. Manoj Kumar and B. Sathish Kumar sought to evaluate the appropriateness of an Ethernet-based industrial network for another time-critical industrial problem: in this case, real-time control of an electrostatic precipitator.
“Out of the many Ethernet protocols available, only some fulfill the requirements,” say the authors. “EtherNet/IP, Profinet, EtherCAT, Sercos III, Modbus TCP, Ethernet Powerlink are the protocols that are suitable.”
The authors chose to analyze and compare two protocols—EtherCAT and Ethernet/IP—on the basis of their frame structures, synchronization and performance characteristics. Since the working principles of the two protocols are quite dissimilar, they presented a separate discussion for each. Here’s what they found on the “suitability of Ethernet/IP and EtherCAT for industrial time-critical applications.”
The application
An electrostatic precipitator is a device used to clean the air flowing out from an industrial plant by removing dust particles using electric charge. A typical industrial plant has four electrostatic precipitators that are monitored by a main computer (A) via four secondary computers (B). Each precipitator is split into eight different ways, each having nine different fields.
All these are controlled by devices, and the instantaneous device data are sent to the secondary computers for verification purposes. Thus, there are 72 nodes in total on each of the Ethernet cables for each electrostatic precipitator. If there is a malfunction sensed by one of the nodes, that information must be sent to the main computer as soon as possible, and the time delay should be less than a second.
The authors conclude that “EtherCAT is expected to perform well within the constraint of data transfer within one second. Moreover it is relatively simpler to implement and is available as open source code. Ethernet/IP, on the other hand, has a much larger footprint with installed capacity in over a million nodes, but requires special hardware (ultra high performance scanners) to achieve data transfer rates of less than a second.”
To learn how different industrial Ethernet protocols compare when it comes to safety applications, attend The Automation Conference. TAC 2014 is being held May 20-21 at the Chicago Marriott O’Hare. Register online or call with questions: 800-355-5595 and ask for Courtney Richards at ext. 113.
