ABB AC500-S Safety User Manual page 400

Safety times
Safety function response time
DANGER!
For safety time critical applications, one has to take into account that AC500-S Safety I/O modules
satisfy the requirement of IEC 61131 (PLC standard) to bypass a potential undervoltage event with a
duration of up to 10 ms. During this undervoltage effect of up to 10 ms, AC500-S Safety I/O modules
deliver the last valid process value before the undervoltage was detected for safety analog input chan-
nels in AI581-S and actual safety digital input and output values for DI581-S and DX581-S modules.
If the undervoltage phase is longer than 10 ms then module passivation occurs (
"Undervoltage/Overvoltage" on page 70).
End-users, who are not satisfied with the undervoltage detection approach described above (e.g.,
undervoltage events with duration of < 10 ms are frequently observed in their application), have to add
10 ms for AI581-S module in their SFRT calculation to take into account a bypass stage described
above. Normally, periodic undervoltage events with duration of < 10 ms are considered to be low prob-
ability faults in the power supply of the safety system and shall not be included in the SFRT calcula-
tion.
400 AC500-S
Ä Chapter 3.2.3
30.03.2017