PROFIsafe 225
where
• Device_WD1 is an internal input device watchdog time
• F_WD_Time1 is the watchdog time for receipt of the new valid telegram (from the
input device to the safety PLC)
• F_Host_WD is the watchdog time of the safety PLC
• F_WD_Time2 is the watchdog time for receipt of the new valid telegram (from the
safety PLC to the output)
• Device_WD2 is an internal output device watchdog time.
Instead of WCDT values, the calculation uses watchdog times. See AC500-S Safety
User Manual (3ADR025091M0207 [English]) for details.
For example, when using the ABB AI581-S as the input device, the SM560-S safety
PLC and the FSO module as the output device, SFRT can be calculated as follows:
SFRT = Device_WD1 + 0.5 x F_WD_Time1 + F_Host_WD + 0.5 x F_WD_Time2
+ Device_WD2 + Longest ∆T_WD
= 76.5 + 15 + 6 + 45.5 + 50 + 45.5 = 238.5 ms
where
• Device_WD1 = 76.5 ms
• F_WD_Time1 = 30 ms
• F_Host_WD = 6 ms
• F_WD_Time2 = 91 ms
• Device_WD2 = 50 ms
• Longest ∆T_WD = Max (0.5 x F_WD_Time1; 0.5 x F_WD_Time2) = 45.5 ms
(all other used WCDT values are equal to their corresponding watchdog times).
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