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S5-95F
Execution of the Background Test
All test components of the background test are stored in a list and are automatically called and
executed by the operating system. Processing of the tests is organized so that all tests are
executed once per hour.
Tests with runtimes of more than 5 ms (see Table 9-11) are subdivided by the S5-95F into several
test segments, so that processing of one test component can be distributed to several PLC cycles.
This distribution to several PLC cycles minimizes fluctuations of the PLC cycle times occurring as a
result of the tests.
The load on the cycle time through tests is low. With a PLC cycle time of 200 ms, the S5-95F
processes a test segment of approx. 5 ms in each cycle. The runtime of a test segment is approx.
30 ms in the case of complex I/O tests only.
Note
If you do not call up function block FB252, the S5-95F executes all test components
automatically except for the short-circuit test (AUFT:0FH).
Calling Up Test Components in the Control Program
If you use function block FB252 to explicitly request a test, then the S5-95F executes the requested
test immediately. The background test initiated by the operating system is not affected by the test
initiated by the user.
You may only activate one user-initiated test at a time. Before you activate a new test (e.g. in
another part of the program), the last test must be completed. If not, none of the tests started will
be completed. You should therefore always evaluate the information returned in the parameter
assignment error byte.
Calling Up a Test Component for DQ Test only in the Control Program
Since the outputs are briefly switched off during the DQ test (see section 4.3), it is possible that
quick-reacting actuators drop out unintentionally during operation. That is why you should not have
the S5-95F execute the DQ test automatically (background test), but execute it at defined, non-
critical system statuses using function block FB252.
Therefore call up FB252 for all non-critical system statuses by means of parameter BED = 1 (see
Table 9-10). With the prerequisite that these non-critical system statuses occur at intervals
the S5-95F will no longer execute the DQ test as a background test. The DQ test is carried out at
the first non-critical system status (within the test cycle of 1 h), and is not repeated in the current
test cycle.
Depending on the parameterization of FB252, the DQ test is executed in one PLC cycle (parameter
EINZ=0) or is distributed to several PLC cycles (parameter EINZ=1).
EWA 4NEB 812 6210-02
Blocks and Their Functions
1 h,
9-17
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