Safety Integrated Level and Performance Levels for Machine Safety

Before a safety (fail-safe) circuit can be designed and applied to a machine, the required level of safety must be determined.  This is done by performing a risk assessment of all parts of the machine in question.  Based on this assessment, either a Safety Integrated Level (SIL) (SIL1, SIL2, or SIL3) or a Performance Level (PL) (PLa, PLb, PLc, PLd, or PLe) is assigned to each part of the machine.  IEC 62061 addresses SIL levels and ISO 13849-1 addresses Performance Levels.  While there are two different standards, the scope of each standard is very similar.  Note that either a SIL or Performance Level would be used, but not both.  The figure below shows an overview of the risk assessment process:

Both SIL and PL levels correlate to each other as shown below: