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A concise rundown on what you need to know for emergency stops, machine guarding, safety PLCs, motor drives and robotics.

Understanding the differences of safety standards as it applies to different markets is a key element in developing a product development strategy for different installations and markets. Although in North America, many of the Functional Safety standards are derived from IEC or ISO standards, it’s important to understand how the requirements differ. This article touches on a few of those issues to help both manufacturers of safety related components and system developers better anticipate the future direction of standards, and specifically the differences between the North American standards and the International Standards.

Emergency Stops – In regards to Emergency Stop devices, the requirements used for UL certification and for international requirements are the same. In both cases the standard IEC 60947-5-5 Low-voltage switchgear and control gear -Control circuit devices and switching elements – Electrical emergency stop device with mechanical latching function- is used. Although other standards are referenced both internationally and in the US (e.g. EN 418 and ISO 13850) the ultimate requirements for construction of an eStop are the same for the international requirements as for the US. The US requirements do include an option to use UL991 for hardware.

Machine Guarding – Electro Sensitive Protective Equipment (ESPE) or light curtains, laser scanners etc. are evaluated to IEC 61496 internationally and in the US to UL 61496. Although the IEC version is the third edition, the US the standard is on the first edition. The Standards Technical Panel (STP) that participates in the development and authorization of the standard are currently in the very beginning stage of updating the UL standard to incorporate more or all of the third edition requirements. As an FYI, one of the first steps in this process is for the STP to develop a comparison between the two documents, so that the STP can determine if the standards can be brought together and minimize or eliminate the difference. One known difference however is the allowance of using UL 991 (Tests for Safety-Related Controls Employing Solid-State Devices) and UL 1998 (Software in Programmable Components) as an option to using IEC 61508 for the Functional Safety. It is important to note that this is just an option, and that for those manufacturers developing global product, use of IEC 61508 allows for, at least in terms of the Functional Safety, a single design for both the US and for international markets

Safety Programmable Logic Controllers – Similar to the situation described above in Electro Sensitive Protective Equipment, in the US, Safety PLCs can be evaluated to either IEC 61508 or optionally they can be evaluated to UL 991 and UL 1998. Otherwise the requirements for Safety PLCs can be the same regardless of the region they are being marketed in. As in the situation for motor drives in the US, the manufacturer can optionally have the PLC additionally or only evaluated to a standard such as EN/ISO 13849.

Motor Drives – Since most machinery includes motion control, one of the big issues is the changes between UL 61800-5-2 the draft standard for functional safety for motor drives and the corresponding international version, IEC/EN 61800-5-2 (fully titled Adjustable Speed Power Drive Systems – Safety Requirements – Functional). UL 61800- 5-2 has some differences to point out in regards to EMC. If the manufacturer of the drive does not know the EMC environment; the level shall be based on the levels in IEC62061. If the levels are considered outside the scope, another method can be used. In other words test in accordance with the levels in IEC62061 unless the specific environment and levels are otherwise known. This differs from the IEC/EN 61800-5-2 version in that IEC/EN61800-5-2 requires EMC testing in accordance with IEC 61800-3 only. In regards to high frequency emissions, the requirements shall be as in IEC 61800-3.

So in preparing to achieve global compliance, an understanding of the details of EMC requirements is critical to an efficient development cycle, otherwise it is possible that duplicating the EMC testing is going to be necessary. In addition there are a few details regarding fault exclusion that need to be respected before understanding how to construct the product. It is important to note that although the Functional Safety Standard for motor drives is UL 61800-5-2, if the end use situation calls for it, or the manufacturer anticipates that this will be marketed such that another standard maybe called for, the manufacturer can certainly also have the drive evaluated to other pertinent standards (for example EN/ISO13849).

Robotics – In the US, Robots are evaluated to UL 1740, Robots and Robotic Equipment, as well as the Robotic Industries Association (RIA) standard for Industrial Robots and Robotic Systems, ANSI/RIA R15.06. The UL Standard references UL 1998 (others can be used in its place), however the RIA standard doesn’t directly reference Functional Safety, the standard states in Paragraph 6.4 that safety related software and firmware based controllers shall be evaluated by a Nationally Recognized Test Lab NRTL, to an approved standard for safety devices, which could include UL 1998 (Software in Programmable Components), ISO 13849, or IEC 61508.

The international standard, ISO 10218, titled “Robots and robotic devices — Safety requirements for industrial robots points directly to ISO 13849 for safety related controls. ANSI/RIA R15.06 is currently under revision (expected in 2nd half of 2012 or possibly early in 2013) to incorporate the requirements found in ISO 10218 with direct references to ISO 13849, as well as IEC 62061, titled “Safety of machinery — Functional safety of safety-related electrical, electronic and programmable electronic control systems.”

As the global supply chain continues to shrink and safety equipment suppliers search to expand their business, being able to develop one product for all markets, and to design it to one set of requirements is always the goal. Although in most of the above cases there are some differences between the requirements for the US market and the global market, understanding the differences will allow manufacturers to minimize the development time and expense of manufacturing a safety product.

For further information on Functional Safety please contact Kevin Connelly at UL: call 631-546-2691 or e-mail Kevin.Connelly@ul.com

General Disclaimer: This article was provided by UL and represents their views on this topic.  The information in this article is for informational purposes only. Please consult with an expert in the field that is knowledgeable about your application prior to using information contained in this article.

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