Related: Digital Domain
Twenty years ago, Ethernet was dismissed for industrial networking. But slowly, out of the rat’s nest of front-office data networks, Ethernet has reached out and touched the plant floor. More than touched, in fact. Analyst firm ARC Advisory Group Inc. (Dedham, MA) forecasts that the use of Ethernet-ready products on device-level networks will explode. Explains Harry Forbes, senior analyst at ARC, “Ethernet is becoming an intrasystem interface.” Forbes suggests that people are looking at ways to utilize Ethernet for factory control applications that push the proverbial envelope vis-à-vis its networking capabilities.
For a number of reasons, Ethernet is enticing for industrial networking applications. It’s tried and true; that is, it’s popular, widely used, and used for years by information technology (IT) departments (and offices) worldwide. Moreover, compared to proprietary networks, Ethernet networks are easier to install and maintain; the networking technology is readily available, and far less expensive.
There’s another enticement: The ability to standardize an entire enterprise—from the plant floor to the corporate boardroom—on one network. Such a network would greatly amortize the costs of installation, maintenance, and training. What’s more, it would also promise greater access to production data throughout the enterprise, from anywhere around the world.
According to Hirschmann-USA (Pine Brook, NJ), a supplier of networking solutions, “Over the past five years, there have been many enhancements to the Ethernet standards, especially in areas of determinism, speed, and prioritization. There is no longer any reason why Ethernet cannot be used to build deterministic fieldbus solutions that are cost effective and open.”
When first adopted in the mid-1980s as the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard, Ethernet was considered unsuitable on the plant floor. The network protocol was (and still is) nondeterministic. Device response times could not be guaranteed because of data collisions and the delays in retransmitting data. Data throughput was slow. The network medium was subject to electromagnetic interference (EMI).
That was then; this is now. Nowadays, Ethernet now runs over shielded and unshielded twisted pair copper, coaxial, and fully EMI-resistant fiber-optic cable. (There’s another medium. Hang on.)
Next, Ethernet operating speeds across even conventional wire cabling have increased at least an order of magnitude, from 10 megabits per second (Mbps) to 100 Mbps. Automatic switches that negotiate 10/100 Mbps are commonplace, thereby optimizing speed versus service, as well as letting you mix 10 Mbps (Ethernet) and 100 Mbps (Fast Ethernet) devices on the same network. The higher speed also reduces the probability of data collisions (thus lost data). The delays that do exist are so short as to be non-issues. For most factory applications, 100 Mbps Ethernet is deterministic enough.
Today, Gigabit Ethernet is available. This is Ethernet running at 1 Gbps, though the latest push is 10 Gbps. Gigabit Ethernet is primarily targeted for enterprise-wide backbone networks; however, it is showing up in the backbone of distributed control systems in the process industries. Explains Forbes, “It’s just for scalability. When users want to scale their [data] ‘pipe’ bigger, they don’t have to do anything special; they just go buy a little more expensive switch.”
|Industrial Ethernet must be secure, reliable, deterministic|
|Security||Availability||Quality of Service|
|Prevent malicious or un- intentional network disruption||Redundant data connections||Ensure deterministic behavior of critical control traffic|
|Allow access only toauthorized users and authorized applications||Sub-second failover||Low latency|
|Notify of potential security threats||Fast and simple field replacement (no need to reconfigure devices)||Prioritize critical control services|
|Multilayer approach to security||Control of multicast for industrial Ethernet data distribution models|
|Implementation of latest security protocols||Redundant power supplies and multiple alarming options||[Source: Cisco Systems, Inc.]|
The technology evolution most responsible for minimizing Ethernet’s nondeterminism are the advanced switching technologies that let multiple devices simultaneously transmit and receive data over multiple network loops. Unlike an Ethernet hub, which bridges all network ports into a common pool, an Ethernet switch lets users divide a network into virtual local area networks (LANs). This segments devices into logical workgroups, helping local data communications stay local. Ethernet switches also typically have a fast internal backbone, which helps eliminate collisions among data packets and, therefore, lost packets. ARC points out that simply swapping a $400 Ethernet switch for a $100 Ethernet hub can make Ethernet more dependable. Even though both link devices and network rings together, fast switches can quickly swap network lines, thereby responding to anomalies quickly, such as miscommunications, power failures, and device failures.
For instance, the industrialized ED6008 8-port EtherDevice Server from Moxa Technologies, Inc. (City of Industry, CA) has redundant Ethernet ring capabilities so that when any segment of the network is disconnected, the server automatically recovers in 300 ms (with 120 nodes connected and a full load of network traffic). Plus, the server dynamically warns technicians when power fails or a port link breaks. It even sends warning emails when Ethernet traffic builds up.
Adding some intelligence—namely, software or firmware—to the switch improves quality of service (QoS) and adds queue management capabilities. According to officials at Cisco Systems, Inc. (San Jose, CA), “By assigning a priority to time-sensitive data, intelligent Ethernet switches can elevate that traffic above lower-priority data. This ensures that high-priority traffic always traverses the network even if the network becomes congested.” Such capabilities are in the Cisco Catalyst 2955, a 12-port 10/100 Mbps switch for linking programmable logic controllers (PLC) to factory floor networks. The switch has no fans, runs on a 24-volt DC current, operates at extreme temperatures, and can withstand extreme shock and vibration. Depending on the model, the switch can include two single-mode or multimode Fast/Gigabit Ethernet fiber uplink ports—for less than $3,600. The switches also have QoS capabilities that can classify, reclassify, police, mark, and even drop incoming data packets as application priorities require.
The traditional industrial automation vendors are on the Ethernet bandwagon, too. For example, Rockwell Automation (Milwaukee, WI) introduced in April an enhanced Ethernet Networking Interface module for networking Allen-Bradley MicroLogix and CompactLogix controllers by Ethernet. The 1761-NET-ENI Series B module adds several data-handling improvements, including more buffering capacity and additional message queuing. These increase communication speeds and provide higher throughput rates—33% faster upload and download times compared with transfer through the DF1 full-duplex protocol.
Ethernet controllers are also evolving. Motorola Inc. (Austin, TX) has a 32-bit microcontroller with on-chip Ethernet and controller area networking (CAN) interfaces. This literally moves Ethernet connectivity from board level to chip level. The chip can operate as a web server on any Ethernet network running TCP/IP, so for example it can post a status report from a production line controller accessible by your laptop, regardless of where your laptop is connected to the plant’s Ethernet network. The new chip sells for $17.86 in quantities of 10,000, which Motorola says is significantly less than a systems integrator would pay for discrete components.
Who might buy such quantities? Well, Rockwell said in March that 30% of its product line was Ethernet-enabled, and it expected that number to jump to 70% by the end of the year. Siemens Energy & Automation Inc. (Alpharetta, GA) said 70% of its product line, excluding sensors, is Ethernet-enabled. Omron Electronics Inc. (Schaumburg, IL) said that 10% of its products can be directly linked to Ethernet. Three years ago, almost none of these products were Ethernet-enabled.
“In the old days,” explains Forbes, “Ethernet used to operate over a shared medium. Today, it’s still a shared medium. It’s just that instead of it being wired, it’s space—a piece of local space.” This is where “wireless Ethernet” now runs. “Unbounded” Ethernet might be a better term because it can use lasers, microwaves, and spread-spectrum radio frequency transmissions as the communications medium.
Among wireless Ethernet’s attractions are that it is less expensive to install a few wireless access points than to install Category 5 Ethernet cables or fiber; it accesses areas of the factory floor that were heretofore inaccessible; and it helps mobile users stay connected to the plant network. Unfortunately, wireless has a major disadvantage: Data throughput is lower than that in wired networks. That said, several protocols qualify as “wireless Ethernet.” IEEE Ethernet 802.11 is the basic wireless equivalent to IEEE 802.3. IEEE 802.11b has emerged as the standard for wireless Ethernet operating at a theoretical maximum throughput of 11 Mbps (10% of that is typical in a plant) and across the license-free 2.4 GHz radio band. (The 900 MHz band is crowded with consumer products, particularly cordless telephones.) The new Wi-Fi standard, IEEE 802.11g, features throughput up to 54 Mbps, which is 1,000 times faster than the theoretical top speed of conventional “56K” modems that connect the computer to the Internet by telephone. Other wireless Ethernet protocols exist, but those are generally based on proprietary protocols.
According to Cirronet, Inc. (Norcross, GA), which specializes in wireless communications, 802.11 is generally for high-speed/short-range communications. “The 802.11b standard, which has a typical maximum operating range of 300 feet, falls short of expectations on the typical factory floor. To extend its range, an 802.11b-based system requires repeaters and extra base stations, adding expense, unnecessary network complexity and, ironically, extra cabling. Suitable industrial wireless Ethernet links, on the other hand, provide operational range on the order of miles without addition equipment.” For instance, Cirronet’s Ethernet bridges provide up to 1 Mbps throughput across nodes up to 1.5 miles apart—wirelessly.
While wired Ethernet has a way to go yet in factory control applications, some factory applications are starting to go wireless. Datasweep Inc. (San Jose, CA) lets users receive e-mail alerts from a manufacturing dashboard, as well as send transaction data to Datasweep’s Web-based manufacturing execution system. Xora Inc. (Mountain View, CA) connectors add wireless capabilities to enterprise resource planning systems from Oracle, J.D. Edwards, and SAP. Control Technology Corp. (Hopkinton, MA) just released its iPanel Series of Web-Enabled touchscreens for graphically displaying data over corporate Ethernet, Internet, or wireless networks,
In sum, it’s a big Ethernet world out there, right in your factory.