UL Clarifies IEC Guidelines for Safety Features in PLCs

Independent science safety company Underwriters Laboratories (UL) is providing new guidance for manufacturers about how to follow the latest IEC standards for implementing safety features in programmable logic controllers (PLCs).

UL's paper "Programmable Logic Controllers and IEC 61010-2-201" provides an overview of new PLC safety requirements as presented in the standard, and the technical changes that PLC manufacturers must address to certify new and modified PLC designs. It also looks at the technical requirements for the standard and provides information on timelines for transitioning equipment to meet them.

UL verifies, investigates, and tests control systems, industrial equipment, and other components that comply with international safety standards for design and use. PLCs for automation of machinery and factory fixtures are included in these evaluations.

The IEC published the latest standard for PLCs in 2013, but they do not go into effect until April 2016, John R. Kovacik, principal engineer at UL, told Design News in an interview. That has given manufacturers of PLCs time to integrate the requirements into new PLCs and also make changes to older designs to comply with the standards. UL can help them depending on which path they decide to go down, which each have their own challenges, Kovacik told us.

"If the want to reevaluate [older designs] for the new standard, we encourage them to dialog with us and do a thorough review -- an analytic-type review -- against the new requirements to determine if they're going to comply," he said. "That would give them an idea whether or not they should pursue recertifying."

As for ensuring that new products meet the standard, UL also can help them during the design process to meet the requirements before the production of new PLCs, Kovacik said. "We can tell them what they would be up against even before they start to go into production."

While often new standards for safety of electrical components just mean the introduction of new requirements, IEC 61010-2-201 goes one step further and puts PLCs in an entirely different category of products, which changes the methodology for evaluation, Kovacik said.

The previous standard for evaluating safety in PLCs was a standard out of the United States that was based on an industrial control philosophy, he said. IEC 61010-2-201 is an international standard that changed previous requirements to ones based on process control equipment.

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"To be more specific, this would encompass more equipment such as instrumentation, lab instrumentation equipment, recording equipment, and laboratory-type equipment for measuring different types of electrical parameters," Kovacik said. "In general we're talking about the equipment that has traditionally been evaluated differently than industrial control equipment, which was where programmable controllers were previously categorized.

"The advantage of knowing there's a new standard out there is a bonus because they can gear their design philosophy to the new standard," he said. "But the old one, if they want to convert [older products], they have to go through complete reevaluation and there is always the risk that the product might not comply with the new requirements because it was designed with the old requirements."

Specifically, some of the new requirements of IEC 61010-2-201 that differ from the previous standard govern issues of durability of markings when exposed to cleaning materials; insulation; protection against mechanical hazards; risk assessment for mechanical hazards; production line testing; single fault testing; and enclosures.

More about the IEC 61010-2-201 standard and its requirements for manufacturers can be found in the white paper, which can be downloaded from the UL website.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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