Linux Lives on a PLC

About 10 years ago engineers were exploring the limits of uses for Linux, the open-source operating system for computing devices. I’ve followed this project from the beginning. Curt Wuollet, an automation engineer, led a group of developers from the “control list” email user group to initiate a Linux programmable controller project onSource Forge(www.sourceforge.com) dubbed the MatPLC project. In fact, the group completed development of controller software compatible with the IEC 61131-3 programming model promulgated by the International Electrotechnical Commission that would operate on a Linux platform.

When they needed a hardware target with a controller and input/output (I/O) connectivity, Sixnet stepped forward and offered one of its controllers as a platform. Sixnet is an automation company based in Clifton Park, N.Y. that develops and markets remote terminal units (RTUs), controllers, I/O modules, Ethernet switches and other automation components.

Marita Heath, Sixnet director of automation solutions, says that many engineers program in C for control on Linux. It’s popular with original equipment manufacturers (OEMs) who private-brand their machine controllers. “It’s also great for developing industry-specific algorithms, for example those promulgated by the AGA for gas compressors and the like,” she adds. “We have regular distributors who are also systems integrators who like the flexibility. Engineers whose applications need to talk to the Web are fond of PERL on the platform.”

Wuollet suggests a second Linux PLC project on the Web atwww.beremiz.org.

Beremiz is also a free software framework for automation. Its benefits reportedly include the ability to “automate anything,” turn any processor into a PLC, program once and run anywhere, create customizable human-machine interfaces and avoid vendor lock.

This latter was perhaps the driving force for early Linux adopters—and remains so today. The vendor they wanted to avoid was Microsoft. They saw the huge Redmond, Wash. company as a near monopoly and wanted an alternative. Well, now there are a couple.

Source Forge(www.sourceforge.com)

Gary Mintchell,gmintchell@automationworld.com, is Editor In Chief ofAutomation World.