Rockwell Automation FactoryTalk Alarms and Events Quick Start - Manual (Page 211)

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Appendix G
Time synchronization
FactoryTalk Alarms and Events provides excellent resolution and accuracy for alarms
and events time stamps. You can build a very accurate time sequence for events that
led to a failure, or simply to diagnose the exact order of their occurrence. Because the
alarms are generated by the controller, the time-stamp accuracy is a function of the
rate of the controller’s ability to scan the alarm instruction, plus the accuracy of the
controller’s wall clock.
When an alarm instruction is evaluated in code and an alarm transition event occurs
(goes into alarm, or is acknowledged, suppressed, and so on), the instruction
immediately records the current value of the controller’s wall clock. This 64-bit,
microsecond-resolution number reflects the time of the event relative to the
controller’s wall clock in UTC time (no time zone or daylight savings information is
included). When you view this time stamp, either in RSLogix 5000 or in FactoryTalk
View Site Edition, the time zone of the computer running the software is used to
visualize the time value. You can use a distributed system that covers multiple time
zones to display a valid sequence of events at an operator or maintenance station
independently of the time zone the time stamps are captured in.
Coordinating multiple controllers’ wall clocks
Because alarm events can originate in multiple controllers distributed over an
enterprise, it is important to provide a common time reference to set these clocks. A
controller with a wall clock that is out of synchronization with the rest of the
enterprise, will potentially log events out of the time sequence in which they actually
occurred, relative to the other controllers.
Setting the controllers’ wall clocks individually by hand is inefficient. Additionally,
clock drift naturally causes these clocks to record time further and further apart from
each other. There are several automated methods to manage the wall clocks on
multiple controllers, the easiest and most cost-effective of which is the Logix5000
Clock Update Tool.
The Logix5000 Clock Update Tool lets you view and synchronize the system time of
the controllers and devices on a network, using any computer running Microsoft
Windows and RSLinx Classic. You can also schedule automatic synchronization of all
devices. See “Create a synchronization schedule” on page 206.
The accuracy of time synchronization varies based on many factors, including the
network path and what the controller is doing when the time synchronization takes
place. Typical systems using the Logix5000 Clock Update Tool coordinate clocks to
around 300ms. If you need greater accuracy for clock synchronization than the
Logix5000 Clock Update Tool can provide, there are several other hardware-based
options to improve the accuracy of time stamps in the control system. These include
IRIGB, NTP, GPS, and IEEE 1588 Ethernet.