Rockwell Automation FactoryTalk Alarms and Events Quick Start - Manual (Page 21)

1 • Overview of FactoryTalk Alarms and Events services
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Device-based alarm monitoring works like this:
This approach has several advantages over software-based alarm detection:
„ Alarm instructions are programmed only once, and then downloaded to the
controller, which reduces programming effort and errors.
„ Alarm conditions are detected more quickly.
„ Alarms are detected at the same time the logic is being executed.
„ HMI tags or alarms in a Tag Alarm and Event Server are not required, which
reduces overhead and potential tag mapping errors.
„ Alarm state is managed, processed, and preserved by controllers, even if a
computer is stopped.
„ Data polling is eliminated and Alarm status is communicated only when state
changes, which reduces network overhead, controller processing, and improves
overall system performance.
„ Time stamps on alarm conditions are precise, because they are applied in the
controller, and not delayed until they reach the HMI software or Tag Alarm and
Event Server. However, all controllers that produce alarms must have their clocks
synchronized because device-based alarms are stamped with the controller’s time.
The event time is published throughout the FactoryTalk Alarms and Events
system, so inaccurate time stamps can affect where alarms are displayed in the
Alarm and Event Summary or the Alarm and Event Banner, as well as in reports
based on the alarm and event history. For more information about synchronizing
controller clocks, see Appendix G, “Time synchronization”.