Allen-Bradley PowerFlex 527, User Manual

Page: 89 / 176

Rockwell Automation Publication 520-UM002B-EN-E - December 2017 89
PowerFlex 527 Integrated Safe Torque-Off Chapter 4
Probability of Dangerous
Failure Per Hour (PFH) Safety-related systems are classified as operating in a High-demand/continuous
mode where the frequency of demands for operation made on a safety-related
system is greater than once per year.
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).
PFH Data
This PFH calculation is based on the equations from EN 61508 and show worst-
case values.
Determination of safety parameters is based on the assumptions that the system
operates in High-demand mode and that the safety function is requested at least
once a year.
This table provides data for a 20-year proof test interval and demonstrates the
worst-case effect of various configuration changes on the data.
Safe Torque-Off (STO)
Feature The safe torque-off circuit, when used with suitable safety components, provides
protection according to EN ISO 13849 (PLe), Category 3 or according to
IEC EN 61508, EN 61800-5-2, and EN 62061 (SIL CL3). All components in
the system must be chosen and applied correctly to achieve the desired level of
operator safeguarding.
The safe torque-off circuit is designed to safely turn off all of the output-power
transistors. You can use the safe torque-off circuit in combination with other
IMPORTANT
Determination of safety parameters is based on the assumptions that the
system operates in High-demand mode and that the safety function is
requested at least once every three months.
PFD and PFH Data
Attribute Value (Hardwired and Network)
PFD (average) 1.53E-4
PFH 1.7E-9
SIL CL 3
PL e
Category 3
MTTFd (years) 166
DCavg (%) 90 (medium)
HFT 1 (1oo2)
Mission time (years) 20