Ayman Elotaify

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According to IEC 61508, safety functionality should cover the safety loop from sensor to the actuator including, digital input or analog input, logic processing and digital output.
To reilaize the standard IEC 61508 for certain loop, digital / analog module should be fail safe, the blocks used for programming should be certified, and if you used certified blocks the CPU is Fail safe and you can put TUV stickers on it, digital output module should be fail safe.
Please doenload theexamination reportand see chapter 2.2

The system components which are certified ‘safety-related’ are listed in the current revision of the Annexes of the Report to the Certificate Z10 09 07 67803 004. This allows the components to be used to process safety critical signals and functions.
All other components of the S7-400 and S7-300 family are 'interference-free'and allowed to be used; however, they are not certified for process safety critical signals and functions.Using these components does not interfere with the proper functioning of the safety-related modules.