Safety functions: Stop functions and their standard reference

Stop functions are found on almost all machines. EN 60204-1 defines 3 categories of stop function for the various functional requirements:

• Stop category 0
• Stop category 1
• Stop category 2

A category 0 stop leads to an immediate removal of power to the machine actuators. Activation of the mains isolating device automatically triggers a category 0 stop, as power is no longer available to generate the movement.

With a category 1 stop, power to the actuators is maintained to enable a controlled stop.

Stop category 2 is used if power is required even in a stop condition, as power is maintained after the controlled stop.

These stop categories should not be confused with the categories in accordance with EN ISO 13849-1 or EN 954-1, which categorize structures with a specific behavior in the event of an error. For speed-controlled drive systems, EN 61800-5-2 assigns stop functions to the stop categories listed in EN 60204-1.

Application blocks in the drive environment

In addition to general safety functions such as monitoring of safety gates, emergency off/emergency stop function or light curtain evaluation, configurable safety relays also offer special expansion modules and specific application blocks for advanced options such as the safe detection of movement and standstill on drives. Two axes are possible per expansion module, each with eight limit values for speed monitoring, standstill monitoring and detection of clockwise and anti-clockwise rotation. In this way, motion information can be integrated directly into the safety system, irrespective of the drive system you are using.

With normal standard encoders, monitoring is possible up to Category 3 of EN 954-1 or Performance Level d of EN ISO 13849. This is significant for two reasons: fi rstly, there is no need for expensive, safe encoders and secondly, laborious wiring is no longer necessary thanks to the simple “listening function” of the encoder signals – “tapping” the encoder cable via a T-junction. The direct signal tap on the motor encoder minimises the work
involved in the mechanical and electrical design through appropriate adapter cable for the widest range of drives. In the simplest way possible, speed and standstill detection, including evaluation via customized application blocks, is available via plug and play.

EN 954-1 for CE-marking can now be used until December 31st, 2011

December 29^th the new Machinery Directive, 2006/42/EC became effective. On the same day, the Official Journal of the European Union, published a two year extension of the validity of EU safety standard, EN 954-1.

The new date of cessation of presumption of conformity for EN 954-1 is 31 Dec 2011. The two-year extension granted by the EU Commission is less than the three years requested by the EU Standards-making bodies.

The official announcement can be read at

http://eur-lex.europa.eu/JOHtml.do?uri=OJ:C:2009:321:SOM:EN:HTML

During the transition period, which started in 2006, machinery manufacturers can assess compliance of their control systems to the EU Machinery Directive (for CE marking) using either the superseded standard, EN 954-1, or its successor standards, EN ISO 13849-1 (2006 and 2008 editions) and EN 62061 (2005).

Impact on machinery destined for USA and Canada

“It is increasingly likely that machinery purchasers will specify the use of the latest standards (including ISO 13849-1 and EN ISO 13849-1), regardless of whether an “old” standard is still allowed for presumption of conformity in EU.  They have good reason to do this.  They are assured that their equipment meets all of the current EU and International standards, which is extremely important if they choose to re-locate the equipment at a later date when the “older” standards are no longer valid.  And of course from a liability standpoint, machinery purchasers may choose to use the latest standards as an element of their risk management programs,” says Roberta Nelson Shea, General Manager of Michigan-based Pilz Automation Safety.

International Impact

It should be noted that while EN 954-1 is recognized throughout the world, it is not an international standard. This is an important aspect, particularly for machine manufacturers and users that operate internationally. At an international level, ISO 13849-1:2006 (second edition) has already replaced the first edition of ISO 13849-1: 1999, which was based on EN 954-1.

EN 954-1 no longer represents the state of the art

First and foremost, the EN 954-1 represented the state-of-the-art in machinery safety design in 1996. There have been many changes in machine safety and control technology in the last 14 years.

Product-Specific Standards

Many Type B and Type C (product-specific) standards listed under the current Machinery Directive already refer to EN ISO 13849-1 and EN/IEC 62061. These include, for example:

• EN 61496: Safety of machinery – Electro-sensitive protective equipment
• EN ISO 13850: Safety of machinery – Emergency stop – Principles for design
• EN 848: Safety of woodworking machines

Other C standards will gradually be amended accordingly. Once these standards are amended, application of EN 954-1 would no longer enable presumption of conformity for these standards. This leaves machine builders and integrators with the unsettling situation where they either use

• EN 954-1, but instead of using the applicable C level standard instead they comply with the Machinery Directive

OR

• the applicable C level standard which requires EN ISO 13849-1 or EN/IEC 62061

Builders and integrators would then have to ask themselves, What does this mean from a liability standpoint if the machinery is different depending on the approach used?  What does this mean if the machinery is moved in two years? 

Support in converting to the new standards

Pilz has already certified its products to EN ISO 13849-1 and EN/IEC 62061 and has also tailored its services to suit, from training to implementation of providing CE marking services.

What’s more, Pilz’s PAScal Safety Calculator provides a convenient software tool for calculating the performance level and safety integrity level that safety functions can achieve based on the components used. A free trial copy of PAScal is available for download from www.pilz.us. Unlike SISTEMA, PAScal supports EN/IEC 62061 as well as EN ISO 13849-1.

Pilz supports design engineers in the United States, Canada and around the world who have already converted to EN ISO 13849-1 and EN/IEC 62061. At the same time, Pilz continues to provide products, services and technical support for those design engineers who have chosen to continue to apply EN 954-1.

Pilz, the company

The world leader in SAFE automation; Pilz offers a full range of leading-edge safe automation products and services. The company’s innovative technologies and safety expertise provides customers with the leanest and safest solutions.

Products include sensor technology, electrical monitoring relays, and automation solutions with motion control, safety relays, programmable safety and control systems and an operating and monitoring range. Wireless and safe bus systems are also available for industrial networking.

Pilz also provides a comprehensive range of consulting, engineering and OSHA-approved training services. Certified consultants provide a wide range of services in USA, Canada and worldwide including risk assessment, safety concept, safety design, LeanSafe™ services, CE-marking and safety sign-off. Pilz also performs facility safety reviews for due diligence relating to mergers and acquisitions.

For more information visit www.pilz.us or call 1-888-650-PILZ (7450)

The innovative PSENslock series

The innovative PSENslock series, from Pilz Automation Safety L.P. the German manufacturer of safe automation components and systems, takes safety to a new level. It operates magnetically, not mechanically, as do the more traditional systems. "The PSENslock non-contact magnetic interlocking gate switch is an outstanding alternative to traditional mechanical gate switches," said Sales Engineer Ben Harper. "It's safer because it combines secure safety gate monitoring and a non-contact magnetic interlock within the same unit. And because it's mechanically non-wearing, PSENslock has a longer service life."

PSENslock has an electro-magnetic holding force of either 500 N or 1000 N to prevent the unintentional opening of swing gates and sliding gates. Its proven transponder technology is manipulation proof because the switch and actuator are totally different items. This provides an additional measure of safety. Existing mechanical technology, on the other hand, requires the use of a keyed actuator. Consequently, it's possible that this "key" could be damaged, suggesting the door is closed, creating a potentially unsafe condition. Ideal for use in rugged industrial environments, PSENslock is easy to install. With its combination of safe position monitoring and process guard locking, it's suitable for mounting onto standard 45mm profiles around the machine.

PSENslock can be used on flap gates and safety gates and is extremely tolerant to gate misalignment. With bright, double-sided LED diagnostics on both sides; it can be mounted left or right handed. An M12 plug connection allows for simple assembly. "It's really quite an achievement," Harper added. "In addition to the longer life cycle, ease of installation, higher tolerance to alignment, and strong holding force, the PSENslock has the option to include a fully coded switch which is more difficult to defeat and can be wired in series while maintaining the high safety categories that many applications demand."

PSENslock is designed for applications up to SIL3 in accordance with EN/IEC 62061, Category 4 in accordance with EN 954-1 and protection type IP67. In terms of a complete solution, PSENslock can be connected to all Pilz evaluation devices.

Pilz manufacturers a line of safety equipment used in plants. These sensors, relays and other components can be applied as individual pieces or group components to machines throughout many industries where man and manufacturing equipment are utilized together, including automotive, robotics, packaging, amusement, and wind power. The company also provides a wide array of safety consulting services.