Rockwell Automation 21G PowerFlex 750-Series AC Drives Reference Manual - Manual (Page 18)

18 Rockwell Automation Publication 750-RM001F-EN-P - February 2012
Chapter 1 Safety Concept
Performance Level and Safety Integrity Level (SIL) CL3
For safety-related control systems, Performance Level (PL), according to ISO
13849-1, and SIL levels, according to EN 61508 and EN 62061, include a rating
of the system’s ability to perform its safety functions. All of the safety-related
components of the control system must be included in both a risk assessment and
the determination of the achieved levels.
Refer to the ISO 13849-1, EN 61508, and EN 62061 standards for complete
information on requirements for PL and SIL determination.
Refer to Chapter 10 for more information on the requirements for configuration
and verification of a safety-related system containing the PowerFlex 750-Series
drives.
Functional Proof Tests The functional safety standards require that functional proof tests be performed
on the equipment used in the system. Proof tests are performed at user-defined
intervals and are dependent upon PFD and PFH values.
PFD and PFH Definitions Safety-related systems can be classified as operating in either a Low Demand
mode, or in a High Demand/Continuous mode.
• Low Demand mode: where the frequency of demands for operation made
on a safety-related system is no greater than one per year or no greater than
twice the proof-test frequency.
• High Demand/Continuous mode: where the frequency of demands for
operation made on a safety-related system is greater than once per year or
greater than twice the proof test interval.
The SIL value for a low demand safety-related system is directly related to order-
of-magnitude ranges of its average probability of failure to satisfactorily perform
its safety function on demand or, simply, average probability of failure on demand
(PFD). The SIL value for a High Demand/Continuous mode safety-related
system is directly related to the probability of a dangerous failure occurring per
hour (PFH).
IMPORTANT Your specific application determines the time frame for the proof test interval.