Allen-Bradley GuardPLC 1753, Справочник по безопасности

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20 Publication 1753-RM002C-EN-P - September 2008
Chapter 1 Safety Concept for GuardPLC Controllers and GuardPLC I/O
Safety Times
Individual errors that may lead to a dangerous operating condition are
detected by the self-tests and trigger defined error reactions which
transfer the faulty modules into the Safety state within the safety time
of the PES. The following sections describe self-test safety times.
Fault Tolerance Time (FTT)
See DIN VDE 0801 Appendix A1 2.5.3
The fault tolerance time is an attribute of the process and describes
the time span in which faulty signals can be tolerated in the process
without a dangerous condition occurring. If the fault condition lasts
longer than the FTT, the faulty signals can create a dangerous
condition.
Safety Time (of the PES)
The safety time is the time within which the PES (while in RUN mode)
must react after an internal error has occurred.
Seen from the process side, the safety time is the maximum amount of
time in which the safety system must react (reaction time) to a change
in the input signals or module or component failure.
Multiple Error Occurrence Time (MOT)
The occurrence time for multiple faults is the period of time in which
the probability for the occurrence of multiple faults, which in
combination are critical to safety, is sufficiently low.
The multiple fault occurrence time is defined at 24 hours in the
operating system.