Paths to Machinery Directive Compliance

Thursday, September 25, 2014 @ 01:09 PM gHale

By Ellen Fussell Policastro
The best way to comply with the European Union (EU) machinery directive is to abide by standards that support it; look at relevant standards in the machinery environment and use one of those standards that apply to the machinery directive.

“If you do this, you’ll be writing your own declaration of conformity,” said Joe Lenner, senior functional safety engineer at TÜV Rheinland of North America and a keynote speaker during the Siemens virtual Machine Safety World event Wednesday. That declaration of conformity is a requirement going into the EU market. It shows all relevant guidelines have met a certain level. “It’s not a quality or approval mark, but there are certain machines that require independent certification,” Lenner said. These are also dangerous machines.

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Lenner’s presentation helped users understand more about two paths they can take to comply with the machinery directive: EN/ISO 13849 and EN/IEC 62061.

“As a manufacturer you have to comply with requirements of the machinery directive, and the two most relevant standards that apply are EN/ISO 13849 and EN/IEC 62061,” he said. “They both target integrators and manufacturers of machinery and of components that go on machinery.”

The commonality between the two standards is they both require you to have a quality management system. So you need to have a suitable system for managing your design development and change management. “You need document signoff, code reviews, and things of that nature,” he said. “These are absolutes for 62061 and 13849.”

Aspects of 13849
The 13849 standard comes out of ISO, “which is responsible for all things not electrical in general,” Lenner said. “It grew up out of EN 954, which had no reliability components,” he said. “It was strictly a qualitative look and architecture of the system. ISO 13849 is simplified and gives conservative estimates. In general, ISO 13849 is good for more simple well-defined architectures. It is compatible with other methods defined in IEC 62061.”

The scope of this standard covers safety-related controls and safeguarding devices: Mechanical, hydraulic, pneumatic, and electrical. It is designed around specific architectures. If you’re not in one of these architectures, it will tell you to use different models based on IEC 61508 or 62601.

“You can claim compliance with 13849 through categories, which represent the designated architecture,” Lenner said. “If you comply with EN 954 Category 3, you will also be able to comply with 13849. But 13849 brings in diagnostics, so you must have a quality management system in place.”

The categories carried forward from EN 954. They begin with Category B (Basic) and continue with Categories 1 through 4. The Basic category means complying with the standard using basic safety principles and things specified within their limits. “If you use good engineering practices, you should be able to use category B. But there’s no failsafe design,” he said. “In Category 1 you use everything from Category B, but you’ll use well-tried components and well-tried safety principles.” Well-tried components are situations in which all failures can be well understood — relays, resistors, and capacitors. “Anything with complex electronics is not well tried and cannot be Category 1,” he said.

“But what does a failure mean to us? We can break up failures into safe and dangerous,” Lenner said. “They may cause a machine to shut down. These are safe failures. Dangerous failures, however, can have an effect on a safety function performing its task. So you break that down into loss of function. Now you have an unsafe failure that remains undetected. Our goal is to drive down the number of dangerous undetected failures as low as possible.”

Category 2 includes use of well-tried safety principles, “but now we introduce concepts of safety diagnostics,” he said. “If there’s a fault detection, you’ll attempt to shut down and annunciate the fault. There is no high degree of fault tolerance, but it is improved over Category 1 because there are lots of diagnostics.”

With Category 3, you can use well-tried principals and detect a single fault. “You can power up within suitable time intervals, and you’ll be tolerant of a single fault,” he said. “Now we start to see the principles of dual channels. Category 3 is truly a dual-channel architecture. Category 4 has dual principles, but now you’ll be able to tolerate two faults.”

Aspects of 62061
EN/IEC 62061 is the standard for application areas of machine safety. It follows all the same principles of IEC 61508, but it is more simplified. “The requirements are SIL dependent, which means you’ll reduce the risk. It is much more structured along the lines of risk reduction,” Lenner said.

The basis of ISO 62061 comes from IEC and gives you more specific criteria for risk reduction. “If you have mechanical components, you have to consider ISO 13849 on some level. It is preferable for low-complexity systems,” he said. Use ISO 62061 for complex systems and architectures you define yourself and for getting a more accurate calculation.

Either one of these two standards will give you a path of compliance for the machinery directive. Both standards represent state of the art in safety-related functions and systems. “So following either one or both gives you that ability to know you’ve done your due diligence,” Lenner said.

The major difference between the two is 13849 has a broader scope, including hydraulic, pneumatic, and safety structures. It depends on predefined architectures. Conversely, 62061 is for programmable electronic systems. It specifies IEC 61508 for the manufacturing environment. “But remember, 61508 is not harmonized for the machinery directive,” Lenner said. “It is just a basic standard and has no requirement for any specific area, including machinery.”
Ellen Fussell Policastro is a freelance writer based in Raleigh, NC.

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