Rockwell Automation 1715-OF8I Redundant I/O System User Manual - Manual (Page 220)

220 Rockwell Automation Publication 1715-UM001C-EN-P - March 2014
Chapter 6 1715 Redundant I/O System in SIL 2 Safety Applications
Logix System Reaction Time
The following sections provide information on calculating the Logix System
Reaction Time for a simple input-logic-output chain and for a more complex
application using produced/consumed safety tags in the logic chain.
Simple Input-logic-output Chain
Figure 64 - Logix System Worst-case Reaction Time for Simple Input to Logic to Output
The Logix System Reaction Time for any simple input to logic to output chain
consists of these five components.
1. Safety input module reaction time plus input delay time
2. Safety Input Connection Reaction Time Limit
(Read from the Module Properties dialog box in RSLogix 5000 software.)
3. Safety Task Period plus Safety Task Watchdog time
4. Safety Output Connection Reaction Time Limit
(Read from the Module Properties dialog box in RSLogix 5000 software.)
5. Safety output module reaction time
Configuring the SIL 2 Task
Period and Watchdog
This SIL 2 task is a periodic task with priority (1). Refer to the Using
ControlLogix SIL 2 Applications Reference Manual, publication 1756-RM001 .
SIL Task/Program Instructions
The user application must contain a single SIL task composed of programs and
routines. The SIL 2 task must be the controller’s top priority task and the user-
defined watchdog must be set to accommodate the SIL 2 task.
1. Safety Input
Module Delay
5. Safety Output
Module Delay
2. Safety Input Connection
Reaction Time Limit
4. Safety Output Connection
Reaction Time Limit
CIP Safety Network
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3. Safety Task Period +
Safety Task Watchdog
IMPORTANT Motion-related functions are not allowed and must not be used.