Rockwell Automation FactoryTalk Alarms and Events Quick Start - Manual (Page 206)

FactoryTalk Alarms and Events System Configuration Guide
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Coordinated Universal Time (UTC)
Coordinated Universal Time is a real-world time relative to a time constant, but with
no time zone information and no daylight savings time offsets. It is the raw value used
to represent time and also the value required for time stamps in the FactoryTalk
Alarms and Events system. UTC is equivalent to Greenwich Mean Time, with no
daylight savings time offsets.
Advantage of using UTC for time stamps is that distributed events can be compared,
regardless of their geographical location or where they are, relative to Daylight
Savings Time (DST). The software reading the time stamp can then convert UTC time
stamps to local time. Logix 5000 and FactoryTalk Alarms and Events graphic objects
convert UTC time stamps to the local time of the workstation running the software
application.
Time stamps from different sources may or may not be returned in UTC format,
depending on the device generating the time stamp and how it is configured. For
example, a 1756-IB16ISOE module can return time in UTC if configured to do so.
In the Logix system, time is often returned as two 32-bit DINT data types instead of
one 64-bit LINT data type. The FactoryTalk Alarms and Events system requires the
time stamps to use the LINT data type. If a module (for example, the 1756-IB16ISOE
module) returns the time stamp in two DINTs instead of a LINT, you will have to
convert the time format into a LINT. To perform this conversion, an Add-On
Instruction is available for download from the Logix sample code website in the
Rockwell Automation Sample Code Library at http://
samplecode.rockwellautomation.com/. On the search page, in the Family list, select
Programmable Controllers, and then in the Technologies & Functionalities list,
select Add On Instruction. Download the item called Math and Compare
operations with 64-bit Long Integer Tags LINT Data Type in RSLogix5000 ver
16.
Local Time (Wall Clock Time)
Local time (often referred to as Wall Clock Time) is the time in the real world where
the controller is located. This means that Wall Clock time is UTC, but with time zone
and Daylight Savings Time (DST) offsets added.
Local Time is typically used to trigger local events (like turning on a pump at 1:00AM
during shift change). Local time values must be converted to UTC before passing
them to an alarm monitoring system.