Safety in F-Systems
4.8 Safety Requirements
Safety Engineering in SIMATIC S7
4-14
System Manual, 04/2006, A5E00109529-05
Explanations for Table
In general, actuators and sensors are the largest contributor to the failure probabilities in the
above table.
In all cases, the safety function encompasses the entire chain from information acquisition to
information processing to the intended action.
The devices involved, such as an S7 F/FH Systems F-system, sensors, and actuators, must
collectively comply with the SIL or Category determined during the risk assessment.
If control functions and associated protection functions are implemented together in
S7 Distributed Safety or S7 F/FH Systems, operation is in high demand mode or continuous
mode.
Risk Analysis in Accordance with IEC 61508
As shown in the following figure, an F-system prevents potential dangers or reduces them to
a tolerable level through appropriate organizational and technical measures.
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Figure 4-2
Risk Analysis in Accordance with IEC 61508