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Programming
Fail-Safe Systems
5-28
A5E00085588-03
5.3.7 Programming Startup Protection
After startup (cold restart or complete restart (warm restart)), the Safety Program
automatically starts up with the initial values .
Note
When the Safety Program is compiled, additional blocks and calls that must not be
changed are inserted automatically at the beginning of the run sequence in OB
100.
If the process doesn’t permit the Safety Program to start up with the initial values
after an error automatically, a response to startup must be programmed. The
F_START fail-safe block is available to signal a startup of the Safety Program with
the initial values.
The COLDSTRT output parameter signals the occurrence of a startup (cold restart
or warm restart).
Examples
Possible measures for responding to a startup of the Safety Program with the initial
values are as follows:
•
Programming an interlock of the outputs after startup via the passivation
inputs PASS_ON at F_CH_DO. This entails the COLDSTRT output of the F FB
F_START being interconnected with the S input of an SR flipflop (F_SR_FF)
and the Q output of F_SR_FF being interconnected with PASS_ON of
F_CH_DO. This interlock can then be enabled manually:
Using a switch that is requested via a fail-safe digital input module or
Via input at ES/OS via the F_QUITES F FB.
The Q output of the F_CH_DI of the switch or the OUT output of F_QUITES
must be interconnected with the R input of F_SR_FF.
•
Programming of a wait loop so that the internal states of the Safety Program
correspond to the process state again (see the example of reintegration after
startup of the Safety Program).
•
Programming using multiplexers: The output of an F_MUX2_R multiplexer is
controlled by the COLDSTRT output of the F_START F FB fail-safe block. As a
result, a different program branch to that in the F cycle can be executed after
startup.