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

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5 Safety times

5.1 Overview

Errors in the system may lead to dangerous operating conditions. Potential errors are detected
by the safety module background self-tests, which trigger defined error reactions in safety mod-
ules to transfer faulty modules into the safe state. In this chapter, we list various safety times for
AC500-S safety modules and AC500-S safety PLC as a system.

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 92: Fault reaction times in AC500-S safety modules
Module
AC500-S safety CPUs
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, 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 input signals or module failures.
SFRT is one of the most important safety times, because it is used in time-critical safety applica-
tions, like presses, to define a proper distance for a light curtain or other safety sensor to protect
people from potentially dangerous machine parts.
SFRT for PROFIsafe devices can be defined as, based on
Equation 1: SFRT = TWCDT + Longest ∆T_WD
where
● 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);
● 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 safety modules during the signal transfer. It is enough to
consider a single fault only
2020/06/19
Fault reaction time
Internal faults (e.g., RAM cell fault) External faults (e.g., wrong wiring)
< 24 h
< 24 h
< 24 h
< 24 h
Ä [8].
3ADR025091M0208, 12, en_US
Safety function response time
Not applicable
< 1.9 s
< 0.5 s
< 0.8 s
Ä [8]:
Safety times
317