Siemens CPU 410-5H Process Automation - Page 119

Link-up and update
8.3 Time monitoring
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA
119
1. Based on section Performance values for link-up and update (Page 120) with 170 Kbytes
of user program data:
T
P15_AWP
= 194 ms
Check: Since T
P15_AWP
= 194 ms < T
P15_HW
= 660 ms, continue with
1. Based on formula [3], we obtain the recommended max. inhibit time for priority
classes > 15:
T
P15
= MAX (194 ms, 140 ms)
T
P15
= 194 ms
This means that by setting a maximum inhibit time of 194 ms for priority classes > 15 in
STEP 7, you ensure that any signal changes during the update are detected with a signal
duration of 1250 ms or 1200 ms.
Remedies if it is not possible to calculate T
P15
If no recommendation results from calculating the maximum inhibit time for priority
classes > 15, you can remedy this by taking various measures:
● Reduce the cyclic interrupt cycle of the configured cyclic interrupt.
● If T
TR
times are particularly high, distribute the slaves across several DP master systems.
● If possible, reduce the maximum update time of switched devices on the IO subsystem.
● Increase the baud rate on the affected DP master systems.
● Configure the DP/PA links and Y links in separate DP master systems.
● If there is a great difference in changeover times on the DP slaves, and thus (generally)
great differences in T
PTO
, distribute the slaves involved across several DP master
systems.
● If you do not expect any significant load caused by interrupts or parameter assignments
in the various DP master systems, you can also reduce the calculated T
TR
times by
around 20% to 30%. However, this increases the risk of a station failure in the distributed
I/O.
● The time value T
P15_AWP
represents a guideline and depends on your program structure.
You can reduce it by taking the following measures, for example:
– Save data that changes often in different DBs than data that does not change as
often.
– Specify a smaller DB sizes in the work memory.
If you reduce the time T
P15_AWP
without taking the measures described, you run the risk that
the update operation will be canceled due to a monitoring timeout.
Calculation of the maximum communication delay
Use the following formula:
Maximum communication delay =
4 x (maximum inhibit time for priority classes > 15)