Siemens SIMATIC Operating Instructions Manual page 165

CRC Signature
The validity of the process data in the safety message frame, the accuracy of the assigned
address references and the safety-relevant parameters are ensured by means of a CRC
signature contained in the safety message frame.
Dark Period
Dark periods occur during switch-off tests and during complete bit pattern tests. During these
tests, test-related 0-signals are switched to the output by the fail-safe output module while
the output is active. The output is then switched off briefly (dark period). A sufficiently slow ->
actuator does not respond and remains switched on.
Discrepancy Analysis
The discrepancy analysis for equivalence/nonequivalence is used with fail-safe inputs to
detect faults 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, a
discrepancy error exists.
A discrepancy analysis is carried out between the two input signals of the 1oo2 sensor
evaluation in the fail-safe input module.
Discrepancy Time
Discrepancy time is a period of time assigned for the -> discrepancy analysis. If the
discrepancy time is set too high, the fault detection time and -> fault reaction time are
extended unnecessarily. If the discrepancy time is set too low, availability is decreased
unnecessarily because 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.
Fail-Safe Modules
ET 200pro modules that can be used for safety-related operation (-> safety mode) in the
ET 200pro distributed I/O device. These modules are equipped with integrated -> safety
functions.
ET 200pro Distributed I/O System - Fail-Safe Modules
Operating Instructions, 05/2007, A5E00394073-02
Glossary
165