236 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 page 228
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
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