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Automating Manufacturing Processes with Ethernet-Enabled I/O Modules, Linux - page 3

What's A PLC?

  • October 9, 2002
  • By Rob Reilly

Dan Naughton, Woodhead Connectivity's Engineering Manager said, "TCP/IP socket performance [with Linux] was better than the Windows 95/98 operating system during our testing." "Also, touchscreen support for Elo Touch monitors and additional drivers for network cards and video adapters were included in the Redhat 7.2 Distribution," Naughton added.

Naughton said they had troubles with the NT version, getting the dreaded blue screen after simply trying to change the network card. "Linux is very stable," he concluded.

For automation software on the Linux box, the team turned to the OpenController.org project. OpenController.org had a ladder logic design program, as well as a runtime control engine on the Linux box that runs the electropolishing machine. The GUI portion of both the LadderDesigner and the runtime control engine were written using wxWindows, an Open Source C++ GUI framework for cross-platform compatibility.

"We originally tried Embedded uClinux on the I/O modules themselves, but ran into implementation problems," Naughton said. "The kernel was not stable and we eventually abandoned it," he further commented.

Naughton and the team are the usual technology enthusiasts employing Linux servers at work and of course, at home. They have worked with embedded Linux, RTLinux and other operating systems.

There are other control programming methods for creating instruction sets for PLCs, but Naughton said that ladder logic was the standard for industrial control. "Around 98% of industrial automation is PLC ladder logic," Naughton explained.

The working electropolishing machine took 10 weeks to build. The team had worked with the OpenController.org project for 6 to 9 months prior to starting the electropolishing machine project. The runtime program ended up being about 400 lines of ladder logic and 1500 lines of mnemonics. Mnemonics are the actual instructions that are executed on the PLC to control the I/O module. The OpenController.org project will be posting the actual ladder logic program file use for this machine on the project website.

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