Glossary
ET 200S Distributed I/O System - Fail-Safe Modules
Installation and Operating Manual, 08/2008, A5E00103686-07
211
CRC signature
The validity of the process values in the safety message frame, the accuracy of the assigned
address references, and the safety-related parameters are validated by means of the CRC
signature in the safety message frame.
Dark period
Dark periods occur during shutdown tests and complete bit pattern tests. The fail-safe output
module switches test-related zero signals to the active output. This output is then briefly
disabled (= dark period). An -> actuator with sufficient lag does not respond to these signals
and remains switched on.
Discrepancy analysis
The discrepancy analysis for equality/non-equality is used at fail-safe inputs to detect errors
based on the timing of two signals with the same functionality. Discrepancy analysis is
initiated when different levels (when testing for nonequivalence: same voltage levels) are
detected at two associated input signals. The signals are checked to determine whether the
difference (when checking for nonequivalence: the consistency) has disappeared within a
programmable period known as the -> discrepancy time. If not, this means that a
discrepancy error exists.
The discrepancy analysis compares the two input signals of the 1oo2 sensor evaluation in
the fail-safe input module.
Discrepancy time
Configured time for the -> discrepancy analysis. If the discrepancy time is set too high, the
times for fault detection and -> fault reaction are extended unnecessarily. If the discrepancy
time is set too low, availability is decreased unnecessarily since a discrepancy error is
detected when, in reality, no error exists.
DP master
A master that behaves in accordance with IEC 61784-1:2002 Ed1 CP 3/1 is known as a DP
master.
DP slave
A DP slave is a slave operated on PROFIBUS with the PROFIBUS DP protocol that behaves
in accordance with IEC 61784-1:2002 Ed1 CP 3/1.
F monitoring time
-> PROFIsafe monitoring time
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