Rockwell Automation 1756-HIST2G FactoryTalk Historian ME 2.2 - Manual (Page 139)

8 • A DMINISTERING THE M ODULE
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at boot time, the module will achieve runtime time precision by periodically
resynchronizing with the time source.
Clock Drifts
It is generally a good practice to synchronize all devices to a single reliable time
source. Even though clock drifts may occur among the module, FactoryTalk
Historian SE or the PI server, and any controllers, efforts should be made to minimize
this. To adjust for time variations caused by clock drifts forward or backward in time,
the module will slew or step as needed. Module log files are provided for time-related
warnings and information.
If you have configured your points to have a high speed scan type and the controller
time drifts more than 30 seconds either forwards or backwards or the module has
been running for more than six and a half days, a message similar to the following is
generated in the system log:
27-Jan-10 13:24:09 logixd [WARNING] Logixd detected a controller
time shift greater than thirty seconds on High Speed Trend in-
stance 7 running on Data Source
All_Type_Combination_07072009_v17_1_1. The Trend was restarted.
Current Time
The module’s current time is displayed in the Current Time field. To update the time,
refresh your browser window.
The module’s current time cannot be edited through the Current Time field. To edit
the module's current time, select the Manual Set option or one of three time
synchronization options. When you click [Save], the module will reboot
automatically, and the Current Time field will then display the time based on the
selected time source.
Battery Clock
The module’s real-time clock is maintained by a rechargeable, zero-maintenance
battery. It is not field-replaceable. The battery powers the real-time clock for a
minimum of 20 days when the module is not powered on. The module requires power
for approximately 20 hours before the battery is fully charged.
When changing the module time, do not change the module time to a time earlier than
the current module time if Data Collection has already been started.