Rockwell Automation FactoryTalk Alarms and Events Quick Start - Manual (Page 29)

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Chapter 3
Define device-based alarms in Logix5000 controllers
To set up device-based alarm monitoring, you program alarm instructions, that are
available with RSLogix 5000 v. 16 or later, and download them to a Logix5000
controller. The controller detects alarm conditions and notifies alarms and events
services of alarm states. Software components publish this information to a device
server, where it can be logged to a database, and viewed, acknowledged, suppressed,
enabled, or disabled from FactoryTalk View graphic displays.
FactoryTalk Alarms and Events can handle many different types of alarms. The
controller limits the alarms to digital and analog. An analog alarm instruction
monitors two types of alarm conditions: Level and Rate of Change. A tag-based alarm
server supports three alarm types: Digital, Level and Deviation.
A digital alarm instruction is based on the input rung state (in ladder logic) or on the
alarm input (for function block). The trigger condition compares the value of the tag to
either zero or one.
An analog alarm defines a condition that evaluates a single analog tag against up to
four limit values (high-high to low-low) and up to two rate of change limits (positive
and negative).
Alarm buffering during loss of connection to the controller
To receive device-based alarms, the alarm server (RSLinx Enterprise) establishes a
subscription to the alarms in the Logix controller. The controller maintains a
connection to each subscriber and monitors the status of that connection.
As alarm state changes occur, the controller caches information such as timestamps,
alarm state and associated tag values, and transmits the information to all of the
subscribers.
If any subscriber fails to confirm the receipt of the alarm information, or if the
connection to a subscriber is not good, the controller stores the undelivered alarm
information in a 100 KB buffer. Each subscriber has its own buffer and
communication problems with one subscriber do not interfere with alarm delivery to
other subscribers. When the buffer is full, newer alarm information is discarded and a
FactoryTalk Diagnostics message is logged. The buffer is created when the subscriber
establishes its initial connection, and is maintained for a length of time after a
subscriber loses its connection. The length of time is specified in the Buffer Timeout
setting on each RSLinx Enterprise device shortcut. See Chapter 4, “Create a new
shortcut to the controller”.
If your FactoryTalk application does not include Logix5000 controllers, or if your
controllers are not programmed with the new alarm instructions included in RSLogix
5000 v. 16 or later, see Chapter 5, “Add an OPC Data Server for third-party
controllers” and Chapter 6, “Add a tag-based alarm server for Logix5000, PLC-5,
SLC 500, or third-party controllers”.