Configuring a Windows 7 PC as a Time Sync Server


AS or other device unable to reach external time servers

Product Line

SmartStruxure Solution


Automation Server on closed network

Windows 7


AS will not sychronize the time with a local NTP such as Windows 7 (32 or 64 bit) without it first being configured.


Windows 7 has a NTP procedure to setup, it is as follows:
   1. In the 'Services' window(part of Administrative Tools) Stop the 'Windows Time' service if already running. The 'Startup Type' could be set as Manual or Automatic depending on the user needs.
   2. In the Registry Editor following changes to be made under the Key
       ** Config -> AnnounceFlags = 5.
       ** HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\W32Time\TimeProviders\NtpServer -> Enabled = 1.
   3. Start the 'Windows Time' service in the 'Services' window(part of Administrative Tools).

Note: NTP uses UDP Port 123


The Internal Workstation or PC with NTP enabled but is not able to access External NTP servers/time will not sync with the AS because the AS does not trust the time provided. The local PC has to synch with trusted NTP servers, then it is a trusted time, and the AS will sync. Sites without External NTP so the internal NTP can sync will not be suitable for the AS as an NTP.

Below is a Wireshark capture using filter udp.port == 123 indicating the “Leap indicator” bits are 11, meaning “clock unsynchronized”.

NOTE: The NTP client in the AS may ignore the time sent by the NTP server if the root dispersion is greater than 'X' seconds (unknown at this time). see LL#17955 for information on how to determine whether this is a problem at the site and how to resolve it.

Note: Test Lab results show that once validated and synchronized, the AS asks the time from the NTP about every 17 minutes.
Two enhancements have been requested for a future release:
1.Workstation gets an alarm if the NTP is not a valid reply
2.A tickbox setting in Workstation so the ES/AS can accept an invalidated reply(time)

There is a workaround a site may want to investigate. Meinberg NTP is a third party NTP server that runs on the Win7 OS and provides NTP by synchronizing with four or more Internet clocks, and is a trusted time source in NTP. The ES/AS responds to this and trusts the time. The clocks sync, both for the Operating System, the ES and for the AS. It is not a supported PSS tool/workaround, but it does fix the issue of the ES/AS not trusting the time.