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By Rich Merritt
Whenever we ask instrument and control engineers what they think about the Windows OS, we get comments all the way from "It's the Wal-Mart of operating systems," to "I would never trust Windows with a process control system." To many, only "real" controllers, such as a DCS or a PLC, can be trusted for the actual control functions.
As it turns out, PC-based hardware and Windows operating systems have crept into many types of "real" controllers, including PLCs, PACs and even—Gasp!—distributed control system (DCS) controllers. These bastions of reliability have succumbed to the lure of Windows-based connectivity and universal open software. Proprietary hardware and operating systems are nearly a thing of the past. Everything is "open" today.
Readers of Control magazine seem to be grudgingly accepting PC-based industrial computers (ICs) into their plants. Or maybe they are buying these devices because they are the best solutions available.
We found many applications for industrial computers (IC), but only a few ICs are actually being used for process control. Test, monitoring and human-machine interfaces (HMI) are the most common applications.
Figure 1. An industrial computer from Rockwell Automation is controlling this oil extraction process in New Zealand. Industrial computers are everywhere in your plant.
of New Zealand does use a PAC for process control—a Rockwell Automation ControlLogix PAC—to control an oil extraction process in the Cheal oil field in western New Zealand (Figure 1). According to Alan Hooker, instrument and electrical engineer with Independent Technology, the contractor that built the station, Austral needed an automated system that could control and monitor everything from oil temperature to equipment performance, while capturing data to comply with regulatory requirements.Austral Pacific Energy
"The complex nature of Cheal's production and information needs demanded a system that could maximize uptime," said Hooker. "The site can only handle around five hours of downtime before it begins to lose heat and, if all heat is lost, it takes up to two weeks to heat the wells up to the desired temperature."
The ControlLogix PAC provides all the capabilities of a traditional DCS system and manages thousands of discrete, process and safety I/O points. "Using ControlLogix controllers helps lower the cost of ownership, provides better flexibility and offers more scalability than a traditional DCS system," Hooker said.
Industrial computers and HMI/SCADA software are posing real competition to DCSs, and the Austral project illustrates that whatever a DCS can do, so can a PAC.
But wait! Isn't a PAC a hybrid PLC? True, but another definition applies: A PAC is an industrial computer with PLC capabilities. Furthermore, many PLCs have adopted a PC-like architecture.
Andrew Craig, automation manager of FlavourCraft in South Africa, uses Beckhoff PLCs to control batches of flavorings and food formulations. "Beckhoff uses standard PC CPUs in their PLCs and I/O stations, which really brings the costs down," says Craig. "This also means that their processing power jumps every year as the CPU speeds increase."
So, is the Beckhoff PLC a PAC? It is getting harder to tell the difference, but it is certainly an industrial computer, and it is being used for process control.
So what is an industrial computer? Why is it different from the $400 desktop PC at Best Buy or Circuit City?
Miko Grika of Beckhoff says, "Office PCs are designed for consumers and are almost never ‘industrial' in any way. Consumer PCs are not designed for plant environments and are more susceptible to heat, vibration and general wear and tear. They're designed for sitting on desks, not for mounting in control cabinets, and there's no guarantee that the consumer PC will be capable of real-time computing, a necessity for many applications. ICs such as those from Beckhoff are designed for real-time computing and microsecond-level performance."
What makes an industrial computer so rugged? Various vendors use sealed faceplates, tough enclosures, solid-state memories instead of rotating disks, low-power CPUs, industrial-grade power supplies and careful layout of components for heat dissipation and shock protection.
What some IC vendors do is replace some of the commercial, off-the-shelf (COTS) components with more rugged ones, such as the Intel SOC (system on a chip), AMD GX Series or the Advantech EVA SOC. In fact, you will probably find such SOCs embedded in devices all over your plant—in PLCs, PACs, Ethernet switches, field instruments, calibrators, I/O modules and DCS controllers. "Embedded systems have become ubiquitous," says Mike Berryman of Advantech. "We find them literally everywhere, especially in the industrial environment."
Most likely, you won't use an office computer as an I/O module, but you might try to use it for a non-critical HMI or test-and-measurement application. Accessories such as shock mounts and air-conditioned enclosures make it possible to use an office PC on the plant floor. You have to be careful to allow sufficient air flow to the fans and keep electrically noisy components and vibration away from the PC, but this method works—probably not in a critical control application though.