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Rockwell Automation Publication 1715-UM001J-EN-P - December 2020
Chapter 8 Using SIL 2 Add-On Instructions with 1715 Redundant I/O Modules
Safety Reaction Time Calculations
The 1715 AOIs process data at a rate of the module RPI / 2. For example, if the
1715-IF16 RPI = 100 ms, the 1715 IF16 AOI processes the most recent packet
every 50 ms. This provides a compromise between controller bandwidth (not
processing the packets too often using old data) and overall 1715 screw to screw
performance. Because the 1715 AOIs run on a time basis, the input module AOI
and the output module AOI can be asynchronous. See
for more
information. The periodic task rate affects the actual process rate and periodic
task scan time.
The worst-case safety reaction time can be calculated using the formulas that
are shown in the following example.
For the following example, assume the following:
•
1715 Input Module RPI = 60 ms
•
1715 Output Module RPI = 80 ms
•
SIL 2 Task Period = 30 ms
•
SIL 2 Task Watchdog = 20 ms
•
AOI Module RPI=60 ms
1715-OB8DE
OB8DE_Simplex_SIL2
Simplex
501
1715-OB8DE
OB8DE_Duplex_SIL2
Duplex
541
1715-OF8
OF8I_Simplex_SIL2
Simplex
951
1715-OF8
OF8I_Duplex_SIL2
Duplex
964
N/A
CRC Calculator
N/A
N/A
Table 46 - Maximum Scan Rates Measured - The L75 Controller was used for taking measurements.
Module
Add-On Instruction
Scan Rate µs (max measured)
Table 47 - Maximum Scan Rates V3 Measured- The L75 Controller was used for taking measurements.
Module
Add-On Instruction
Scan Rate µs (max measured)
1715-AENTR
AENTR_SIL2_V3
Duplex
507
1715-IB16D
IB16D_Simplex_SIL2_V3
Simplex
982
1715-IB16D
IB16D_Duplex_SIL2_V3
Duplex
1035
1715-IF16
IF16_Simplex_SIL2_V3
Simplex
676
1715-IF16
IF16_Duplex_SIL2_V3
Duplex
696
1715-OB8DE
OB8DE_Simplex_SIL2_V3
Simplex
950
1715-OB8DE
OB8DE_Duplex_SIL2_V3
Duplex
1012
1715-OF8
OF8I_Simplex_SIL2_V3
Simplex
1048
1715-OF8
OF8I_Duplex_SIL2_V3
Duplex
1055
1715-IF16
IF16_Simplex_HART_SIL2_V3
Simplex
692
1715-IF16
IF16_Duplex_HART_SIL2_V3
Duplex
715
1715-OF8
OF8_Simplex_HART_SIL2_V3
Simplex
1058
1715-OF8
OF8_Duplex_HART_SIL2_V3
Duplex
1071
N/A
CRC Calculator_V3
N/A
N/A