How to Configure Time Synchronization on PCS 7 Terminal Bus Systems: DCF77 Client vs Network Time Protocol (NTP)

In SIMATIC PCS 7 distributed networks, non-PCS 7 industrial PCs (such as a SIMATIC IPC847D running Windows Server 2008 R2) connected to the terminal bus require precise time synchronization to ensure chronological sequence of events (SOE) alarm logging. In legacy PCS 7 versions, the standalone DCF77 Client V2.00 (available on the PCS 7 Software Support & Tools DVD) provided radio-clock synchronization; however, modern operating systems (Windows 10, Windows Server 2012 R2, and newer) are incompatible with the legacy DCF77 client. The standardized method across modern systems is utilizing Network Time Protocol (NTP) configured via Windows Time Service (W32Time) or Group Policy, synchronizing to a central SICLOCK or GPS master clock.

Importance of Time Synchronization Across PCS 7 Plant and Terminal Buses

In modern process automation, millisecond-accurate time synchronization across all Automation Stations (AS), Operator Stations (OS Servers, OS Clients), and auxiliary industrial PCs (such as SIMATIC IPC847D) is an essential operational requirement:
* Sequence of Events (SOE): When a plant trips, dozens of interlocks, circuit breakers, and valve limit switches trigger within a 100-millisecond window. If station clocks deviate by even 500 ms, the WinCC alarm journal records cause-and-effect sequences backwards, preventing engineers from identifying the root cause.
* Redundant Database Mirroring: WinCC server redundancy and Process Historian database replication rely on synchronized Kerberos timestamps; clock skews exceeding 1 second trigger replication timeouts and authentication rejections.

The Legacy DCF77 Client Service: Deployment and Operating Limits

In legacy PCS 7 versions (V7.0, V7.1, V8.0, and V8.1), Siemens provided a specialized utility known as the DCF77 Client:
* The software service is located on the PCS 7 Software Support & Tools DVD within the separately orderable Software Support Package (order number 6ES7650-4XX08-0YT8) under:
02_Timesynchronization\DCF77Client_V2.00
* The DCF77 Client installs as a lightweight background Windows service.
* It receives time broadcast telegrams from a physical DCF77 radio receiver or a central SICLOCK master transmitter connected to the serial COM port or terminal bus, periodically disciplining the local Windows system clock without requiring full WinCC software installation.

Operating System Incompatibility Barriers in Modern PCS 7 Releases

As industrial IT shifted toward modern operating systems (Windows 10 Enterprise 2015 LTSB, Windows Server 2012 R2, Windows Server 2016, and PCS 7 V8.2 / V9.x):
* Driver Deprecation: The legacy DCF77 Client V2.00 service architecture is completely incompatible with 64-bit kernel driver signing policies and modernized Windows time-stack APIs in Windows 10 and Server 2012 R2.
* Attempting to run DCF77 Client V2.00 on these operating systems results in silent service crashes or Windows Event ID 7000 service startup failures.
* Consequently, Siemens officially transitioned the recommended time synchronization architecture to native Network Time Protocol (NTP).

Configuring Network Time Protocol (NTP) via Windows Time Service

To synchronize any stand-alone industrial PC or OS station to the PCS 7 time master without legacy client software:

Configure Local Group Policy (gpedit.msc):
* Open the Local Group Policy Editor on the IPC.
* Navigate to: Computer Configuration > Administrative Templates > System > Windows Time Service > Time Providers.
* Double-click Enable Windows NTP Client and set to Enabled.
* Double-click Configure Windows NTP Client and set to Enabled:
- NtpServer: Enter the IP address of your central SICLOCK master or active OS Server followed by flag ,0x8 (e.g., 192.168.1.10,0x8).
- Type: Select NTP.
- SpecialPollInterval: Set to 60 (polls every 60 seconds).
Restart and Register the Windows Time Service:
* Open an elevated Command Prompt and execute:
cmd net stop w32time w32tm /unregister w32tm /register net start w32time w32tm /resync /force
Verify Synchronization Status:
* Execute w32tm /query /status to confirm that the IPC is synchronized to the central master with minimal phase offset.

Comparison of Industrial Time Synchronization Protocols

The table below compares the time synchronization methods used across SIMATIC PCS 7 networks.

Synchronization MethodProtocol / TechnologyTypical PrecisionSupported Operating SystemsHardware Master SourceDCF77 Client V2.00Proprietary Siemens Service~10 msWindows XP, Server 2003, Server 2008 R2Physical DCF77 Receiver / COM portNetwork Time Protocol (NTP)Standard RFC 5905 (UDP 123)1 ms to 5 msAll Windows VersionsSICLOCK TC 400 / GPS MasterSIMATIC Time Sync (CP)S7 Protocol / SNAP Broadcast1 msAS Controllers / WinCC Plant BusCP 1623 / CP 443-1 MasterPrecision Time Protocol (PTP)IEEE 1588< 1 microsecondSpecialized Industrial EthernetSCALANCE XR-500 Master Clock

Verification

To confirm that the IPC847D or OS station is synchronized:
1. Open an elevated command prompt on the target station and run: w32tm /query /status.
2. Verify that Source displays the IP address of the central master clock and Leap Indicator reports 0 (no warning).
3. In WinCC Explorer on an OS station, open the Time Synchronization editor: confirm that the station is synchronized to the master.
4. Trigger a test event or alarm: verify that the recorded timestamp matches the central GPS/SICLOCK master time down to the second.
5. In Windows Event Viewer under System, verify that event source Time-Service logs event ID 35: The time service is now synchronizing the system time with the time source.

Limitations and Operational Precautions

Never operate two conflicting time synchronization services (such as DCF77 Client and Windows NTP) simultaneously on the same machine; competing services cause clock jitter and oscillation.
Ensure UDP Port 123 is open in Windows Firewall across all private and domain profiles to permit NTP traffic.
Avoid using public internet NTP servers on air-gapped industrial control networks; deploy dedicated physical master clocks (e.g., SICLOCK TC 400 with GPS antenna).
Virtual machines hosted on VMware ESXi must have VMware Tools periodic clock synchronization disabled to prevent conflicts with the central NTP master.

Engineer FAQ

Where can I find the DCF77 Client V2.00 installer?

It is located on the 'PCS 7 Software Support & Tools DVD' under 02_Timesynchronization\DCF77Client_V2.00. It is part of the separately orderable Software Support Package (order number 6ES7650-4XX08-0YT8).

Can DCF77 Client run on Windows 10 or Server 2012 R2?

No. Siemens officially confirmed in the PCS 7 V8.2 Readme that DCF77 Client V2.00 is incompatible with Windows 10 and Windows Server 2012 R2. Use native Windows NTP instead.

How accurate is NTP synchronization across the terminal bus?

On a standard switched local area network (LAN), Windows NTP achieves time synchronization precision between 1 and 5 milliseconds, which is fully sufficient for sequence of events (SOE) alarm logging.