Narrowing the PC, PLC Gap

Two Camps Continue to Compete for Business, but Draw Closer to the Same Architecture

By Rich Merritt

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Once again, as part of our anniversary retrospective of content we created during the past 15 years, we offer up, as it originally appeared in February 2001, a discussion of the role of PC-based control in discrete manufacturing and its impact on applications that once were the sole domain of PLCs. It was becoming clearer that PCs might not take over the industrial world after all, but the landscape was undergoing permanent change. Note the number of companies that no longer exist as standalone entitities.

The subject comes up every year, and for good reason. Choosing whether to use a PC or a PLC as the heart of a machine or system controller can make or break an OEM. Software and technology change regularly — sometimes daily — so OEMs try to keep up as best they can. Someday a killer app will come along to tilt the scales in one direction or another, they fear, and nobody wants to miss it.

Over the past year or so, we've seen three major trends developing that will impact the PC vs. PLC decision for OEMs: communications, web-enabling, and hybrid PLCs, some of which are becoming PCs.

PLCs Becoming PCs
Aside from the technical arguments, marketing issues may have an impact on the decision making. Semicore Equipment makes vacuum deposition equipment (Figure 1), which it sells to sophisticated, high-tech customers such as Nortel and Lucent. "We used PLCs for 17 years," says Trey Haight, automation engineer. "We switched over to pure PCs for a few years, and now we've returned to the new PLC hybrids."

Semicore president Matt Hughes says vacuum deposition systems have been around for 40 years and the players in the industry are well-known. "What sets us apart from our competitors is that we are using the latest automation equipment, and this is important to our customers," he says. "In fact, we recently sold a system to Nortel, and they came back and asked us if we could install our controls on two of their older machines."

The need to support Ethernet and web communications functions is driving many PLC vendors to add PC-like features to stay competitive. "Information requirements from the plant floor are pushing a PC mindset into the controls arena," says Diane Trentini, manager of enterprise solutions at Optimation Technology, a system integrator.

As a result, some PLCs are actually becoming PCs. This began when PLC manufacturers offered coprocessors and plug-in modules to compete with PCs, but now the functions are being built in. "Most PLC manufacturers are introducing products with more low-cost, PC-like connectivity capabilities and open features integrated into the CPU, such as an Ethernet port," says Jim Allison, PC controls product manager at AutomationDirect. "PLC systems are becoming network-aware."

"Some PLC companies are offering slot PCs and soft PLCs to address customer demand for high-level PC features," adds Mark Smith, business development manager, CTC Parker Automation.

Patrick Rousselot, product director at control system developer AlterSys, says, "PLC manufacturers try to maintain their reliability advantage [over PCs] by integrating new technologies directly into their hardware, and the result is a PC in a PLC box."

AutomationDirect was one of the first to try this with its WinPLC product, a low-end PLC with the Windows CE operating system, Think & Do software, and HMI capability. Introduced in April 1999, it is a hybrid of PLC and PC technology.

At the upper end are the Rockwell Automation line of Logix PLC/PC hybrid controllers, WinAC soft PLCs from Siemens E&A, ONC from Omron Electronics, MachineLogic from CTC Parker Automation, and similar systems that blend PLC-like hardware with PC processors and software.

David Gee, vice president of Steeplechase Software, says this is a continuing trend. "PLC makers are aware they will never be able to keep up with the PC industry, so they are moving to adopt PC technologies," he says. "This trend will continue until PLCs are PCs running specialized applications software. Hybrid PC/PLCs are just a stepping stone."

This sentiment is shared by many on the PC side, who agree that hybrids are just the next generation in the PLC evolution to the PC architecture.

Omron Electronics has a different perspective. They believe the hybrid platform is gaining acceptance because of its functionality. "We believe the hybrid product is more than a niche product, and we plan to extend the line," says Dave Quebbemann, Omron's industrial automation marketing manager. "Because they combine the best of both platforms, hybrid controllers will gain acceptance in the industrial market."

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