Allen-Bradley 1756-L6 Series, Reference Manual, Page: 96 / 134

96 Rockwell Automation Publication 1756-RM001I-EN-P - May 2012
Appendix A Reaction Times of the ControlLogix System
Remote Chassis
Configuration Figure 52 shows an example system where the following occurs:
• Input data changes on the input module.
• The data is transmitted to the controller via the network communication
modules.
• The controller runs its program scan and reacts to the data change,
including sending new data to the output module via the network
communication modules.
• The output module behavior changes based on the new data received from
the controller.
Figure 52 - Remote Chassis Configuration of Digital or Analog Modules
Calculating Worst-case
Reaction Time The formulas for calculating worst-case reaction times with no system faults or
errors differ slightly for digital or analog I/O modules, as shown in the following
sections. The diagnostic test interval for ControlLogix modules is 8 hours, which
defines the worst-case reaction time for ControlLogix SIL 2.
For Digital Modules
Use this formula to determine worst-case reaction time for digital modules in
local or remote configurations:
Worst-Case Reaction Time with no faults or errors =
(Input Module Delay + Input Filter Time) + (Input Module RPI x 4/8/16…
≥
100 ms)
(1)
+
(SIL 2 Task SIL 2 Task Watchdog) + (Output Module RPI x 4/8/16…
≥
100 ms)
(1)
+
(Output Module Delay).
Module delay times are listed in the ControlLogix I/O Modules Specifications
Technical Data, publication
1756-TD002 .
Output
Module
Controller
Network
Communication
Module
Input
Module
Output
Module
Network
Communication
Module
Input
Module
(1) Multiply the module RPI by 4, then 8, then 16, and so on, until the result is at least 100 ms.