Pilz PNOZsigma safety relays approved for nuclear industry

The chosen PNOZsigma products - PNOZ S4, S5, S7 and S9 - had already demonstrated compliance with IEC 61508 through certification by independent organisations BG and TUV. As safety is clearly of paramount concern in the Nuclear Industry, ONR guidelines insist that UK Nuclear Site Licensees must furthermore fulfil an 'intelligent customer' role when implementing 'smart' components, which requires them to view the evidence supporting the claims made in the certification ('smart' components contain firmware with the inherent potential to contain unrevealed faults, hence the need for substantiation).

This process of substantiation was carried out using the UK nuclear industry standard Emphasis tool. Following initial auditing, three engineers from Sellafield Ltd carried out the audit at the Pilz headquarters in Ostfildern, Germany, together with PNOZsigma development team members and Alex Bryce, the Systems & Solutions Manager at Pilz UK.

Following further tests at Sellafield Ltd, including the seismic evaluation of the PNOZsigma in a control panel, the components are now fully approved for use in Nuclear Safety Systems at Sellafield Ltd and throughout the UK nuclear industry; the PNOZ S9 is approved to IEC 61508 SIL 1, while the PNOZ S4, S5 and S7 are approved to SIL 2.

Sellafield Ltd was impressed by the high standard of documentation behind the procedures for design, development and control. Pilz was also complemented on its workflow details, quality management systems and overall commitment to product quality. In addition, Sellafield Ltd was impressed with the two on-site EMC chambers, and the temperature and ingress protection testing equipment.

The testing team was praised for its level of detail, and the development team for its level of knowledge, experience and vigilant preparation that enabled the audit to be completed in just three days.

Austin Dale, Senior Engineer, CE&I Safety Systems, Design Capability at Sellafield Ltd, comments: "From the assessment we can see that Pilz use all the right tools, techniques and have the right attitude and culture. We were really impressed and could see that Pilz had made even more progress and improvements since first developing the PNOZsigma Relays."

Emphasis - the standard tool for substantiation of 'smart' components

The HSE has stated that IEC 61508 "will be used as a reference standard for determining whether a reasonably practicable level of safety has been achieved when electrical, electronic or programmable electronic (E/E/PE) systems are used to carry out safety functions."

Therefore, compliance with IEC 61508 is key. Manufacturers often demonstrate compliance with IEC 61508 and other related standards through certification by an independent organisation. All UK Nuclear Site Licensees must fulfil an 'Intelligent Customer' role that requires them to view the evidence supporting the claims made in the certificates - and this is the expectation of the ONR.

Many items must be considered when carrying out a product substantiation, so the Emphasis tool has been developed. This extremely detailed process is broken down into three phases:

• Phase 1, Pre-qualification: Investigates the top level Functional Safety Management Issues
• Phase 2: Investigates the hardware procedures and capabilities
• Phase 3: Investigates the software and other in-depth issues to obtain a final Emphasis rating for the instrument

Each phase contains questions - well over 200 in total - that look into many aspects such as the development lifecycle, requirements specifications, design specifications, test specifications, traceability and even the interrogation of the software. For each question, evidence of the answer given is required and an audit must be performed whereby the supplier has to prove or show this evidence and compliance.

Around 30 Emphasis audits have been completed so far by Sellafield Ltd and the other UK-based Nuclear Licencees. Devices, such as the PNOZsigma, which have passed the audit are then placed on a register available to all involved in nuclear industry applications to show the products suitable for use on these sites.

About PNOZsigma safety relays

Pilz PNOZsigma safety relays benefit from the following features:

• Widths from 12.5 mm - hence the require minimal cabinet space and save costs
• Selectable operating modes and timers enable each unit to be flexible in its application
• Applicable to many different safety functions
• Diagnostics in seconds via six LEDs
• Easily expandable

Follow the link for more information about Pilz PNOZsigma safety relays.