Self-Tests And Command Tests; Logical And Timed-Based Program Execution Monitoring - Siemens SIMATIC S7 F Manual

Safety Mechanisms
3.5

Self-Tests and Command Tests

Self-Tests
Self-tests are carried out in the S7 F/FH system to detect faults. The duration of the
cyclic self-tests can be set during configuration (the default is 90 mins).
Note
Only settings of up to 12 hours are permitted for the S7 F/FH Systems.
You cannot modify safety-relevant self-tests for the S7 F/FH Systems with the
SFC 90 "H_CTRL". If you do, the Safety Program will become disabled at the
latest after 24 hours. It is not permitted to switch test components off or on
(submode 0 .. 5 from mode 20, 21 and 22).
For the same reason, you must not disable updating with SFC 90 "H_CTRL" for
too long.
Execution (program run, entire safety-related hardware) and the test result are
checked in the Safety Program by an F test block (F_TESTC) that is inserted
automatically when the Safety Program is compiled.
Command Tests
Some commands are tested in the quickest cycle of the Safety Program. These
command tests are implemented in the F_TEST block, which is included
automatically when the Safety Program is compiled.
3.6

Logical and Timed-Based Program Execution Monitoring

Program Execution Monitoring
CPU or RAM Faults can corrupt the correct execution of the program. Logical and
timed program execution monitoring and data flow monitoring can detect this.
Logical Program Execution and Data Flow Monitoring
During compilation, fail-safe blocks are automatically inserted in the CFC chart for
logical program execution monitoring and data flow monitoring: In each run-time
group with fail-safe blocks, one F_PLK block and one F_PLK_O block is inserted.
The F_PLK is called before the outputs, and the F_PLK_O after them.
Fail-Safe Systems
A5E00085588-03
3-5