Connections for Safety I/O Modules
During module configuration, you must define the module. Among the Device Definition
parameters with safety I/O modules, you must choose how module is configured.
The choice depends on whether the project is downloaded to the controller that owns the
module configuration, that is, the owner-controller, or to a controller that is
listening to modules in a project, that is an external means controller.
A real-time data transfer link is established between the controller and the module that
occupies the slot that the configuration references.
When you download module configuration to a controller, the controller attempts to
establish connections to each module in the configuration. An owner-controller
establishes two connections (safety input and safety output). A controller that is
listening to the module establishes one safety input connection.
Because part of module configuration includes a slot number in the remote I/O system, the
owner-controller checks for the presence of a module there. If a module is detected, the
owner-controller sends the configuration. One of the following occurs:
- If the configuration is appropriate to the module detected, a connection is made and operation begins.
- If the configuration is not appropriate to the module detected, the connection request is rejected and the Studio 5000 Logix Designer application indicates that an error occurred.The configuration can be inappropriate for many reasons. For example, a mismatch in electronic keying that helps prevents normal operation.
The owner-controller and external means controller monitors its connection with a module.
Any break in the connection, for example, the loss of power to a remote I/O system,
causes a fault. The Studio 5000 Logix Designer application monitors the fault status
tags to indicate when a fault occurs on a module.
Producer/Consumer Communication
PointMax I/O modules use the Producer/Consumer communication model to produce data
without a controller polling them first. The modules produce the data and
controllers consume it. If the connection is a multicast input connection, then
mulitple controllers can consume the input data, including the owner-controller and
external means controller.
Connection Reaction Time Limit With Safety Modules
Setting the RPI on safety modules is not as straightforward as setting it on standard
modules. With safety modules, the Connection Reaction Time Limit configuration
affects the RPI that is used for a module.
The Connection Reaction Time Limit defines the predicted period of 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%.
IMPORTANT:
To determine what is appropriate, analyze each safety point. The default
Timeout Multiplier of 2 and Network Delay Multiplier of 200 creates a
worst-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.
For more information on specifying RPI rates, see the Logix 5000 Controllers Design
Considerations Reference Manual, publication 1756-RM094.
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