Traditional fieldbuses or industrial networks do more these days than send data from instruments or sensors to a controller and back to a control element. Today, more of that data travels to the enterprise network for applications such as asset management, SCM, and ERP.
While traditional fieldbus protocols have proven useful to transport data on the plant floor, giving the same protocols a ride on an Ethernet backbone is a trend that’s probably here to stay.
Most controls professionals involved with industrial networks realize Ethernet is relatively inexpensive, thanks to readily available off-the-shelf (OTS) components, and its physical and transport layers are open and present themselves in a fashion that can be well understood. Ethernet still is working out its problems for control-centric tasks—but they’re not insurmountable.
Whether you’re planning a traditional fieldbus network or an Ethernet variant, there are tools, training and critical tips from experienced users available to help you in the design, installation, and troubleshooting/maintenance phases.
Know What It Takes
While learning fieldbus technologies might seem daunting to facility electricians and instrument technicians, the adoption of fieldbus technology, is the cornerstone of a successful implementation,” says William Dolan, PE, principal I&C engineer for Genzyme Corp., a biopharmaceutical producer that uses Foundation fieldbus, Profibus-DP, AS-I, and DeviceNet for its various processes. “The traditional tools alone, which include an instrument screwdriver and a digital volt meter (DVM), will not be sufficient to maintain a fieldbus system. While many of the bus diagnostic tools are resident within the host system, facilities personnel must be trained extensively in each of the buses.”
|FIGURE 1: ELIMINATE RAT'S NEST|
Four fieldbus types provide a simplified, easier to maintain and troubleshoot installation. Source: Genzyme Corp.
Network designers might be tempted to select the latest technologies for new networks, given the apparent upside, but Doug Taylor, principal engineer at system integrator Concept Systems, Albany, Ore., has a practical suggestion. “Using a mature technology usually results in a higher initial system cost, but can lead to a lower maintenance cost (See Figure 1). The embrace of new technologies often can result in a lower initial system cost at the risk of more exposure to long-term downtime costs because of inadequate training. Designers should gauge the level of the maintenance team’s abilities [and resultant training needs] carefully when selecting communication technologies.”
You think you want to install Ethernet? Make sure you’re properly briefed. “Designing an Ethernet network requires a well-trained understanding of the bandwidth and protocol requirements of the equipment to be networked,” says Bill Persyn, project lead at Polytron, Norcross, Ga., provider of PLC and HMI programming development and other automation services. “Once this has been quantified, the engineer can specify the various switching equipment and media.” For example, switches that support IGMP snooping are a must for EtherNet/IP systems, says Bennet Levine, R&D manager at Contemporary Controls. Throw in VLANs gateways and routers, and you might be ready for a crash course in Ethernet.
That’s really the point. You need to be sure you and your coworkers are properly trained and oriented, even if the project is being handled by a third-party. A day will come when you take ownership.
How to Find the How To
There are resources available to help you better understand industrial networks (See Training and Tools sidebar for more details.). Larry Komarek, Phoenix Contact product manager in automation for the Americas, suggests, for starters, a primer course in Ethernet from a commercial entity such as Cisco, which has several certificates for Ethernet training. Another organization, Building Industry Consulting Service International (BICSI), while mainly focused on building infrastructure, provides various levels of telecommunications training—including cabling, LANs, wireless, and RCDD (Registered Communications Distribution Designer). Komarek points out some other organizations that can help: Foundation fieldbus, ODVA for EtherNet/IP, IAONA, ModbusIDA, and the Profibus Trade Organization.
Lee College in Baytown, Texas, is a major learning center for Foundation fieldbus and Profibus networks. Chuck Carter, principal investigator for NSF projects at Lee College, just had concluded a Foundation fieldbus course when we spoke to him for this article. One of Carter’s major concerns is that the training must reinforce the critical need to take documentation seriously when designing networks.