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Rockwell Automation Publication 1756-UM013B-EN-P - October 2019
Chapter 1
Digital Safety I/O Module Operation in a Control System
Requested Packet Interval
The Requested Packet Interval (RPI) is a configurable parameter that defines a
rate at which the owner-controller and the module exchange data.
You set the RPI value during initial module configuration and can adjust it as
necessary after module operation has begun. Valid RPI values for 1756
ControlLogix Digital Safety I/O Modules are 2…500 ms.
Connection Reaction Time Limit With 1756 ControlLogix Digital Safety I/O Modules
With 1756 ControlLogix digital safety I/O modules, the Connection Reaction
Time Limit configuration affects the module RPI.
The Connection Reaction Time Limit defines the maximum time that is allowed
between valid safety packets on the associated connection. If the Max Network
Delay exceeds the Connection Reaction Time Limit, a connection fault occurs.
By default, the Connection Reaction Time Limit is four times the RPI.
Use the default values for Timeout Multiplier (2) and Network Delay Multiplier
(200). The Network Delay Multiplier value is in terms of percentage. Thus, 200
means 200%.
For more information on how to specify RPI rates, see
.
Also see:
• GuardLogix 5580 and Compact GuardLogix 5380 Controller Systems
Safety Reference Manual, publication
• Logix 5000 Controllers Design Considerations Reference Manual,
publication
IMPORTANT
You can change the RPI while the project is online. If you change the RPI
while the project is online, however, the connection to the module is closed
and reopened in one of the following ways:
• You inhibit the connection to the module, change the RPI value, and
uninhibit the connection.
• You change the RPI value. In this case, the connection is closed and
reopened immediately after you apply the change to the module
configuration.
IMPORTANT
To determine what is appropriate, analyze each safety channel. The default
Timeout Multiplier of 2 and Network Delay Multiplier of 200 creates a
worse-case input connection reaction time limit of 4 times the RPI, and an
output connection reaction time limit of 3 times the RPI.
Changes to these parameters must be approved only after a thorough review
by a safety administrator.
Summary of Contents for 1756 Series
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