Siemens SIMATIC ET 200S Installation And Operating Manual page 177

Dark Period
Dark periods occur during switch-off tests and during complete bit pattern tests. This
involves test-related 0 signals being 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 equality/non-equality is used with fail-safe inputs to detect
errors based on the timing of two signals with the same functionality. Discrepancy analysis
stars when different levels (when checking for non-equality: the same level) of two related
input signals are detected. The signals are checked to establish whether the difference
(when checking for non-quality: the match) has disappeared following a selectable time
known as the discrepancy time. If not, a discrepancy error is recognized.
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 configured 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 because a discrepancy error is detected when, in reality, no error exists.
DP Master
A master that behaves in compliance with the IEC 61784-1:2002 Ed1 CP 3/1 standard 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 compliance with the IEC 61784-1:2002 Ed1 CP 3/1 standard.
F monitoring time
-> PROFIsafe monitoring time
Fail-Safe Modules
ET 200S modules that can be used for safety-related operation (-> safety mode) in the
ET 200S distributed I/O system. These modules are equipped with integrated -> safety
functions.
Fail-Safe Systems
Fail-safe systems (F-systems) are systems that remain in a safe state or immediately switch
to another safe state as soon as particular failures occur.
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04
Glossary
Glossary-3