Computer clocks don’t keep perfect time and tend to
drift. Since Wonderware Software
products are real-time systems it is important to keep the time correct to
avoid problems like data loss, incorrect data, and a variety of other problems. Such problems can be prevented by
implementing a time sync strategy.
There is a wide range of time sync strategies ranging from
enabling the domain controller’s time sync feature to relying on a feature of Historian
that is on by default. The one strategy
that stands out from the crowd is using a command line program called net time. It is the simplest to implement and works
better than the rest.
Implementing net
time is as simple as creating a Windows Scheduled Task to run the
command “NET TIME \\Historian /SET /YES” every
hour on all control system PCs except the PC selected to be the time
master. The time master PC should sync
to an atomic clock either through the Internet or an NTP time server available
on the LAN. If there is a Historian in
the system it is the preferred time master.
For screenshots on implementing net
time refer to Wonderware Tech Note 882.
If you are using System Platform it would be good to
consider implementing net time inside
of an object. The advantage is
maintenance. A small problem of having a
Windows Scheduled Task is when replacing the PC years later the Windows
Scheduled Task might be forgotten and not migrated to the new PC. The Windows Scheduled Task isn’t remembered
again until there is a problem with time synchronization and it has to be
troubleshot/re-implemented. This problem
can be avoided by implement net time inside a platform object, this way it is
automatically deployed to the computer.
Even the potential problem of the time master’s computer name changing
could be dealt with by doing some engineering. For example, you could place an
attribute on the platform called “TimeMasterName” and use that when calling net time.
It is important to turn off other time sync tools when
implementing net time. When multiple time sync tools are on they
tend to conflict. Below is the list of
commonly used time sync tools on systems.
Exactly how to disable them varies between versions, but a quick Google search
can look up disabling methods.
- · Windows Automatic Time Sync to Internet
- · VMWare’s Time Sync
- · Hyper-V’s Time Sync
- · Historian’s SuiteLink Time Sync (found in the system parameters)
- · The Domain Controller’s Automatic Time Sync (off by default)
Helpful Links
Wonderware Tech Note 882 on using net time. Note that it isn't necessary to make a batch file like the tech note does, a windows scheduled task can run net time commands without a batch file: https://wdnresource.wonderware.com/support/kbcd/html/1/t002685.htm
Microsoft article for Synchronizing to an atomic clock: http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/windows_date_it_overview.mspx?mfr=true
