Fault Reaction Time; Safety Function Response Time - ABB AC500-S Safety User Manual

Safety times

Safety function response time

5.2 Fault reaction time

Fault reaction time is the maximum time between the appearance of the fault in the system and the trigger of
pre-defined error reactions. The table below provides an overview on the longest fault reaction times in
AC500-S Safety modules.
Table 87: Fault reaction times in AC500-S Safety modules
Module
SM560-S Safety CPU
DI581-S Safety I/O
DX581-S Safety I/O
AI581-S Safety I/O
Contact ABB technical support for more detailed fault reaction times of various faults, if needed.
5.3 Safety function response time
The safety function response time (SFRT) is the time within which the AC500-S Safety PLC in the normal
RUN mode must react after an error has occurred in the system.
On the application side, SFRT is the maximum amount of time in which the safety system must respond to a
change in the input signals or module failure.
SFRT is one of the most important safety times, because it is used in time-critical safety applications, like
presses, to define a proper distance for a light curtain or other safety sensor from the potentially dangerous
machine parts.
SFRT for PROFIsafe devices can be defined, based on [8], as :
Equation 1: SFRT = TWCDT + Longest ∆T_WD
where
n TWCDT (Total Worst Case Delay Time) is the maximal time for input signal transfer in AC500-S system
until the output reaction under worst-case conditions (all components require the maximum time);
n Longest ∆T_WD is the longest time difference between watchdog time for a given entity and worst case
delay time. In safety context, to identify SFRT one has to take into account a potential single fault in one
of the components during the signal transfer. It is enough to consider a single fault only [8].
Fig. 126 and Fig. 127 explain SFRT in more details. The model in Fig. 126 and Fig. 127 includes the stages
of input signal reading, safe data transfer, safe logic processing, safe data transfer and safe signal output.
DANGER!
Input delay, input delay accuracy and test pulse low phase are not needed for AI581-S, however, the
worst case fixed internal input delay of 67.5 ms shall be used for AI581-S instead.
396
Fault reaction time
Internal faults (e.g., RAM cell
fault)
< 24 h
< 24 h
< 24 h
< 24 h
AC500-S
External faults (e.g., wrong
wiring)
Not applicable
< 1.9 s
< 0.5 s
< 0.8 s
30.03.2017