Why industrial Ethernet?

Carl Henning -- Control Engineering, 5/1/2006

A number of trends have moved users toward greater implementation of industrial Ethernet. These include:

1. Control: from centralized to distributed. At one time, PLCs (and DCSs) were big, monolithic, rare, and expensive devices. All automation projects' wires came to them. As remote I/O connections progressed from 'dumb' to 'intelligent,' fieldbuses allowed control to move out from the centralized PLC closer to the equipment being controlled. As more intelligent I/O connections are distributed, more bandwidth is needed to communicate among them. As more devices are needed, a larger address space is needed; enter industrial Ethernet with increased bandwidth and a larger address space.

2. Networks: from many to one.Complications abound with more than one bus: learning multiple tools, implementing multiple infrastructures, requiring multiple interfaces between them. A single bus handling I/O needs, peer-to-peer integration, motion control, safety, and vertical integration to plant-wide systems greatly simplifies initial engineering and ongoing maintenance. One is ideal, but there will likely always be a place for actuator and sensor buses like AS-i. Industrial Ethernet is just too much wiring and too much cost for the 1-bit environment. But other aspects are well-served by industrial Ethernet:

Input/Output connections are most people's first thought when they think of industrial Ethernet. Their concept is moving a fieldbus to Ethernet. While certainly one of the most important aspects, if all an industrial Ethernet will do is replace a fieldbus, it won't be the one network that can be used for (almost) all plant automation. Ethernet requires an Ethernet switch with all branches connecting there. The resulting star topology takes away a fieldbus benefit—the bus! Recognizing this, some suppliers have begun building switches into their devices, allowing a 'virtual' bus structure.

Peer-to-peer integration can apply to PLC-to-PLC or equipment-to-equipment. Integrating the equipment into a coherent production line is a challenge requiring programming of each different control device on each piece of equipment. Profinet provides for the 'componentization' of each piece of equipment using a proxy to interface from Profinet to the equipment supplier's standard control network be it Profinet, Interbus, DeviceNet, Modbus, serial, or whatever. This technique also allows existing equipment to be easily integrated—no need to throw out the existing network and start over.

Motion control seems like less of a worry in a discrete automation world, but an ARC Advisory Group study shows that 38% of the 'discrete' market really is some sort of motion control. So if there is to be one network, it needs to handle motion control. Industrial Ethernet, like Profinet, can handle 150 axes in 1 ms.

Safety. North American code now allows safety circuitry to be implemented in PLCs and over fieldbuses. Many industrial Ethernets have announced or released safety protocols. With Profinet, the 5-year-old Profisafe has been extended from Profibus to include Profinet as well.

Vertical integration. Connection to plant-wide systems is easier when the physical layer is the same (Ethernet) and the protocol layers are also the same (TCP/IP).

3. Connections: from wired to wireless. Some projects necessarily require wireless connections; others use them for convenience. Wireless can provide the convenience of being where the problem is when troubleshooting or commissioning a line. It's often necessary to get control signals from moving equipment—especially rotating equipment. Using festooned cables or slip rings can present maintenance headaches and allow intermittent loss of signal. Standard wireless Ethernet connectivity using standards like IEEE 802.11 provides a well-understood, well-supported means to get those control signals from moving equipment.

4. Information Technology: from ignore to leverage. Office networks used to be irrelevant for control engineers. Now the tools the information technology (IT) department uses for the office network are applicable to Industrial Ethernet—plus the knowledge and experience crossing the IT/control engineering boundary. That boundary between departments must come down.

5. Plant Networks: from proprietary to open. During the era of proprietary buses, users were limited to one vendor and a limited selection of devices. With open networks, there are more vendors to choose from and more products available.

Online Extra

Industrial Ethernet: results to gain
Trends that fuel the growth of industrial Ethernet are big-picture, broad industry movements, says PTO’s Carl Henning. But if these movements do not provide real results for the users of the technology, these trends would fade away, he says. Some of these results are easy to quantify in the ROI calculation and some are more intangible.

Here are some of both kinds of results achievable by users of industrial Ethernet, according to Henning:

• Leveraging IT standards, know-how, and tools lowers costs;
• Wireless connectivity simplifies device connections;
• Using devices with integrated switches continues the advantages of “bus” wiring;
• Open standards allow a broad choice of devices and vendors
• The greater bandwidth and the larger address space of Industrial Ethernet permit larger projects;
• A single network simplifies engineering and maintenance plus reduces training requirements;
• Complete projects faster with the configurable peer-to-peer capabilities unique to Profinet;
• Profinet’s peer-to-peer capabilities allow easy and flexible reconfiguration of production line equipment;
• Having motion control on the same network means consistency of tools and knowledge for all types of applications; and
• Integrating safety circuitry onto Industrial Ethernet and into PLCs saves on wiring, hardware, and software. It speeds troubleshooting, too.
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