SIL (Safety Integrity Level) refers to the standards IEC61508 / IEC61511 and describes instruments, which are used for safety-critical applications. In the event of an emergency, they must react safely and place the control circuit into a safe state. On these grounds, all components in the control circuit (sensor, logic, actuator) must have a SIL classification. The control circuit (safety loop), through special parameters (SFF, PFD, FIT), can have its Failure Probability evaluated.