Phase 6 – Validation

How to Verify and Validate a Safety System Design

Using a rigorous Safety LifeCycle approach, manufacturers and machine builders can harness the inherent value of intelligent safety system designs to help drive productivity, reduce labor costs and increase the bottom line. The LifeCycle approach, as defined in standards IEC 61508 and IEC 62061, provides the foundation for this detailed, more systematic design process for machinery applications. Among the most important phases are the final ones – verifying and validating the performance of a safety system design.

At this point in the cycle, the designer has already conducted a risk or hazard assessment, defined the functional requirements of the machine and begun designing the safety system.

First, verification proves the circuit for the safety functions of the machine is working properly and meets the specified requirements. During verification, engineers and electricians test the safety system to make sure it is working while the machine is running. For example, activating an emergency stop (e-stop) to test that the machine will indeed stop running, completes the verification step for an e-stop application.

Next, validation tests the safety functions of the system do what they are designed to do. For example, in a dual-channel e-stop application using redundant control relays, a designer who is conducting the test might inject a human fault between the logic solver and output on channel one, activating the e-stop, to validate the wiring is correct from the input to the logic solver. The designer would then repeat the process on the second channel to make sure it is functioning as planned.

Ultimately, designers must remember that verification is different from validation. Verifying the safety functions of a system requires a plan, must be documented and should include environmental, operational, and maintenance tasks and functions. Validation proves the safety circuit works correctly. It requires fault injection in all identified modes of operation. It also requires circuit evaluation using analytical tools to verify circuit design compliance, component selection verification and systematic analysis.

Today, verification and validation of a safety system must be in accordance with new global functional safety standards. A designer must validate the safety system in accordance with IEC 61508, IEC 62061, EN ISO 13849-1 and 13849-2. Each standard provides a unique definition of validation.

Validation according to IEC 61508 and 62061 means testing the safety related electrical control system, including both hardware and software, to ensure it achieves the functional safety requirements of the specific application. Validation according to EN ISO 13849-1/2 is a planned, documented process that uses both static and dynamic testing, and other methodologies, to show that all safety related parts of control system interact correctly to perform the intended safety function. Requirements of specified performance levels and categories are found in EN 954-1. EN ISO 13849-2 also specifies the conditions under which the validation should be carried out. 

To learn more about this specific topic, please watch the related Webinar SafeDesign: Machine Safety Validation and follow along with the Machine Safety Validation slides.

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Phase 5 – Safety Technologies

Advances in Safety Technologies Reduce Costs, Improve Productivity

A wide range of safety technologies has emerged in recent years, providing multiple methods to control safety functions, detect presence, and safely operate manufacturing machinery. But which technology is best for which application? Should you use a light curtain or a scanner to detect someone’s presence in a restricted area? Should you use an integrated safety controller or would relays suffice on your machine?

Spurred by technology advancements and changes in industry standards, controllers have increased integration between safety and standard control functionality, with single-system platforms making machines easier and more cost-effective than ever. Integration also helps minimize equipment redundancies, improve productivity and minimize design, development and delivery costs.

For presence sensing, safety mats are inexpensive and durable, but could create a slip hazard, and mat sizing is sometimes an issue. Light curtains and scanners are flexible, durable and rugged, but more expensive and environment may be a factor.

Striking the right balance from the range of technology options requires careful consideration of the specific capabilities, limitations and advantages of each.

Rockwell Automation provides guidance on the proper selection of control system safety technologies for your application.

To learn more about this specific topic, please watch the related Webinar SafeDesign: Safeguarding Technologies and follow along with the Safeguarding Technologies slides.

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Phase 4 – Safety Techniques

Safety Techniques to Improve Productivity

A variety of safety techniques exist today to help increase a plant’s productivity, while better protecting personnel and machinery.

Machine safeguards must do several things, including preventing contact with moving parts, and protecting from falling or discharged products. They must also not create new hazards or be easily removed or tampered with. However, there are options in machine control, guarding, barriers, presence sensing, configuration and feed methods that can be employed to mitigate risks while maintaining production.

For example, zone control helps improve productivity while better protecting personnel. This technique provides the ability to implement flexible operational modes, safely slowing or shutting down parts of a production line, while allowing the rest of the line to continue operation. This technique provides a safer working environment and minimizes costs associated with machine downtime.

To learn more about this specific topic, please watch the related Webinar SafeDesign: Safeguarding Techniques and follow along with the Safeguarding Techniques slides.

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Phase 3 – Standards and Compliance

Improving Compliance, Safety, and Productivity

As 2011 comes to a close, machine builders shipping machines into or out ofEuropewill no longer be able to use standard EN 954-1 to show conformance with the European Machinery Directive. The long-standing main standard for design of safety-related control systems in the “machinery safety” sector will expire at the end of this year.

Though the law only applies to European machine builders, or those that ship machines intoEurope, multinational manufacturers and the machine builders that supply them are also affected, regardless of location. Many multinational manufacturers already specify use of the updated functional safety standard EN ISO 13849-1:2006. Uniform standards reduce liability, and ease management of assets. The more current standards also provide for adoption of new technologies, and add a calculation for probability of failure, meaning that the standard ultimately provides machines that are not only safer, but more efficient and productive.

As this trend continues, machine builders that do not conform to current standards, even those outside of Europe, will find themselves specified out of opportunities with larger manufacturers, or facing competition that builds to standards that make them safer and more productive to the user.

To learn more about this specific topic, please watch the related Webinar SafeDesign: Risk Mitigation Techniques and follow along with the Risk Mitigation Techniques slides.

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Phase 2 – Safety Design Methodology

Improving Manufacturing Performance Through Intelligent Safety System Design

Ask any production line manager about the importance of safety and they will likely tell you about the critical role it plays in helping to protect personnel, reduce injuries and meet compliance demands. These are all valid objectives, but manufacturers and machine builders are missing opportunities if they only focus on avoiding negative consequences rather than striving for greater performance – e.g. increased productivity, improved competitiveness and overall profitability.

These days, manufacturers understand that a well-designed safety system can help improve their efficiency and productivity, and machine builders increasingly recognize how safety systems can improve both business and machine performance, helping differentiate themselves to potential customers.

The combination of functional safety standards, new safety technologies and innovative design approaches are positioning safety as a core system function that can deliver significant business and economic value. This includes financial returns beyond the benefits of reducing costs associated with accidents and medical expenses.

To achieve a higher level of functional safety and experience the resulting benefits, system designers must have in-depth understanding of the manufacturing process and a clear determination of machinery limits and functions, as well as a thorough knowledge of the various ways that people interact with the machinery. They also need to take a practical, rigorous approach to safety system design and be willing to implement and apply new safety technologies and techniques.

To learn more about this specific topic, please watch the related Webinar SafeDesign: Modern Safety Designs for Improved Safety and Productivity and follow along with the Modern Safety Designs slides.

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