By Ian Hetherington, VANTAGE

This article suggests methods on how the client’s User Requirement is Specified (URS) and the recording of the verification and validation procedure.

Published in:
Electricity+Control, February 2016 (pages 4 – 8)
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Commissioning a large machine functional safety projectFrom a performance aspect, what is the difference between a regular control system and a Safety Related Control System (SRCS)? A regular control system has an independent and continuous validation of its performance. This is provided by the key performance indicators for the process under control, such as quality and efficiency. The very reason for the control systems’ existence is being challenged on an hour by hour, day by day basss. Can the same be said of an SRCS? No it cannot. An SRCS may only be challenged when a demand is placed on it. There is no independent and continuous validation of its quality of performance. The quality of a regular control system is measured in the very fine confectionary it produces or the excellent motor cars it produces. The scale of quality of an SRCS is measured in two possible ways. Performance Level (PLr) or Safety Integration Level (SIL) If that PLr or SIL was inherently wrong on day one, it will not show up in the quality of that shiny new car or that tasty biscuit. Therefore for the team involved in the delivery of a safety system, it is imperative that a Functional Safety Management Plan is effective in reducing the possibility of systemic design errors and installation errors.

Take note
• It is important to distinguish between a control system and a ‘safety-related’ control system.
• Whereas the former operates all the time, the safety-related control system only has to respond when a demand is placed on it.
• Any design errors may only be detected too late – unless the user requirement is properly specified.

Read the full article on Commissioning a large machine functional safety project in low res PDF format.

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