When a product is getting certified for functional safety, it is essential to have a clear understanding of the safety function.  First, let’s be clear what is meant by the safety function.  IEC 61508-4 describes a safety function as a “function to be implemented by a safety-related system or other risk reduction measures, that is intended to achieve or maintain a safe state for the equipment under control . . .”

The manufacturer of a product may tend to include all the model variations and configurations. After all, the certification process involves significant resources. They want to be sure not to repeat the effort in 12 months just to include another variation.

But the downside to this is a more costly certification. Each variation must be analyzed and the documents reviewed must cover each model. The tables of failure rate data become lengthy or, the worst case data becomes too conservative for most applications.

So before a certification begins there should be a thoughtful evaluation of what is actually needed and going to be used in the safety system.