Siemens SIMATIC S7-400H Manual page 123

Note
Other factors to note when using fail-safe modules are described in the following
manuals: S7-400 F and S7-400 FH Programmable Controllers and S7-300
Programmable Controllers; Fail-Safe Signal Modules. This applies in particular to
module-internal run times in fail-safe modules.
1. For each DP master system determine from the bus parameters in STEP 7
– T
TR
– DP switch-over time (referred to below as T
2. For each DP master system determine from the Technical Data for the switched
DP slaves
– the maximum switch-over time for the active communication channel
(referred to below as T
3. From the technological specifications for your system determine
– the maximum permissible time period for which your I/O modules are not
updated (referred to below as T
4. From your user program determine
– the scan time of the highest priority or selected (see above)
watchdog interrupt (T
– the run time of your program in this watchdog interrupt (T
5. For each DP master system this gives rise to
T (DP master system) = T
P15
Note
If T (DP master system) < 0 the calculation is to be stopped here. Possible
P15
remedies are listed after the following example calculation. Make the appropriate
modifications and start the calculation from 1 again.
6. Select the minimum of all the T
This time is then known as T
7. Determine the share of the maximum blocking time for I/O classes > 15
determined by the minimum I/O retention time (T
T
P15_OD
Note
If T
P15_OD
listed after the following example calculation. Make the appropriate modifications
and start the calculation from 1 again.
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
for the DP master system
SLAVE_UM
)
WA
PTO
+ T
P15_HW
= 50 ms + min. I/O retention time
> T the calculation is to be stopped here. Possible remedies are
P15_HW
DP_UM
).
).
PTO
– (2 × T
+ T + T
TR WA
+ T )
DP_UM SLAVE_UM
(DP master system) values.
P15
.
P15_OD
Linking and Synchronizing
)
)
PROG
PROG
):
6-21
[1]
[2]