Safety Function Blocks
Are you comfortable using advanced safety logic that is embedded in a safety system? Having pre-engineered MooN or CEM function blocks can save engineering and testing time, but deviates from the traditional code-intensive approach. If the supplier is IEC 61508 certified, do you have confidence that the advanced safety function blocks work as intended?
Joanne Salazar
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Safety Function Blocks
I agree that a standardized approach to advanced safety function blocks is better - especially if the supplier is IEC 61508 certified. This embedded logic allows the end user to reduce engineering and testing. You are correct that DeltaV SIS has both CEM and MooN function blocks that simplify complex safety applications, such as burner management.
Joanne Salazar
Safety Function Blocks
IEC1131 compliant function blocks have been used in PLCs for many years. Many users (including myself) have developed our own versions of MooN and CEM logic blocks over the years. The quality of such blocks vary based on who developed it (error handling, mode shedding, provide ability for an operator to switch from 2oo3 to something else when one input has gone bad or suspect etc).
It makes sense that a standardized approach (IEC61508 compliant development by a vendor) would be a better way to go. I do believe that there will be a wide acceptance in the industry for such a product (for both BPCS and Safety Systems implementation). I have seen a DeltaV safety system with such an implementation (using CEM and MooN blocks). But I have not spent enough time to study all the features.