Siemens SIMATIC ET 200SP Product Information page 32

Glossary
Channel-specific passivation
With this type of passivation, only the affected channel is passivated in the event of a →
channel fault. In the event of a → module fault, all channels of the → fail-safe module are
passivated.
CRC
Cyclic Redundancy Check
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 adequate carrier → actuator will not respond to this and will
remain activated.
Derating
See temperature characteristics
Discrepancy analysis
The discrepancy analysis for equivalence/non-equivalence is used for fail-safe applications
to prevent errors from time differences between two signals for the same function. The
discrepancy analysis is initiated when different levels are detected in two associated input
signals (when testing for non-equivalence: the same levels). A check is performed to
determine whether the difference (for nonequivalence testing: the same levels) has
disappeared after an assignable time period, the so-called 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
Configurable time for the → discrepancy analysis. If the discrepancy time is set too high, the
fault detection time and → fault reaction time a re 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.
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ET 200SP distributed I/O system
Product Information, 07/2013, A5E32288220-AA