Performance Level And Safety Integrity Level (Sil) Cl3; Functional Proof Tests; Pfd And Pfh Definitions; Safety Parameter Data - Allen-Bradley PowerFlex 7000 Series User Manual

Functional Proof Tests

PFD and PFH Definitions

Safety Parameter Data

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 IEC 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, IEC 61508, and EN 62061 standards for complete
information on requirements for PL and SIL determination.
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 the Probability of Failure on
Demand (PFD) and Probability of a Dangerous Failure occurring per Hour
(PFH) values.
IMPORTANT Your specific application determines the time frame for the proof test
interval.
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 PFD. The SIL value
for a High Demand/continuous mode safety-related system is directly related
to the PFH.
PFH calculations are based on the equations from Part 6 of IEC 61508.
MTTF and DC
d avg
This table provides data for a 12-year mission time only if the safety function is
demanded at least once every 6 months, and demonstrates the worst-case effect
of various drive configuration changes on the data.
Rockwell Automation Publication 7000-UM203C-EN-P - September 2018
values are based on EN ISO 13849-1.
Safety Concept Chapter 2
11