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Configuring Terminal Bus Time Synchronization for Standalone Workgroup OS Server Pairs

Configuring Terminal Bus Time Synchronization for Standalone Workgroup OS Server Pairs

To configure time synchronization across an isolated PCS 7 network (redundant OS Servers, redundant Batch Servers, and OS Clients in a workgroup without domain controllers or external NTP sources), establish one redundant OS Server as the Active Time Master on the Terminal Bus using the WinCC Time Synchronization editor. On the primary OS Server, enable 'Synchronization via terminal bus' in Master mode broadcasting time frames. On the secondary server, Batch Servers, and Clients, configure them as Slaves set to 'Take time from a specific computer' pointing to both OS Servers. S7 AS stations synchronize via the Plant Bus CP1623 forwarding time frames.

Table of Contents

Executive Summary

In process control architectures operating on isolated, air-gapped industrial Ethernet networks—common in pharmaceutical, defense, and critical infrastructure installations—automation systems lack access to corporate Active Directory domain controllers or external GPS/SICLOCK NTP time transmitters. When deploying redundant OS Servers, redundant SIMATIC BATCH Servers, and multiple OS Clients in a Windows workgroup, maintaining millisecond-level time synchronization across all nodes is critical to preserve chronological alarm logging and audit trail integrity. Configuring the WinCC Time Synchronization editor improperly results in time drift, archive synchronization failures, and diagnostic warnings such as 'No time master available'. Establishing a deterministic Master-Slave hierarchy over the Terminal Bus resolves these challenges cleanly.

Architecture and Fundamental Mechanics

The architecture of time synchronization in an isolated PCS 7 workgroup splits into two synchronization domains: the Terminal Bus (PC-to-PC) and the Plant Bus (PC-to-AS):

1. Terminal Bus Synchronization Mechanics

The WinCC Time Synchronization package (WinCC TimeSync) coordinates all PC stations across the Terminal Bus:
- In an isolated workgroup, external NTP time cannot be ingested. Therefore, the internal hardware real-time clock (RTC) of the primary OS Server serves as the reference master.
- Master Node (OS Server 1): Configured in the WinCC Time Synchronization editor as Master on Terminal Bus. It broadcasts cyclic time frames (every 10 seconds) containing UTC time to the broadcast/multicast address of the terminal bus subnet.
- Slave Nodes (OS Server 2, Batch Servers, OS Clients): Configured as Slave on Terminal Bus set to 'Take time from a specific computer'. Both OS Server 1 and OS Server 2 are configured in the list. The slaves listen for time frames and adjust their Windows system clocks smoothly without backward jumps.

2. Plant Bus Synchronization Mechanics

Automation Stations (S7-400 / CPU 410) require synchronized clocks so that digital input change-of-state alarms (SOE - Sequence of Events) are timestamped at the 1 ms level:
- The OS Server CP1623 communication processor is configured in HW Config / NetPro as a Time Master on the Industrial Ethernet Plant Bus.
- The CP1623 broadcasts SIMATIC time frames across the plant bus, synchronizing the AS CPUs (configured as Time Slaves).
- This guarantees that alarms generated in the AS match the exact timestamps displayed on WinCC OS faceplates.

Step-by-Step Implementation Procedure

To configure time synchronization in an isolated workgroup network:

Step 1: Configure OS Server 1 as Active Master

  1. Open the WinCC project on OS Server 1 (or ES for OS1).
  2. In WinCC Explorer, double-click Time Synchronization.
  3. Check the box Synchronization via terminal bus.
  4. Select the option Make this computer the time master (Master mode).
  5. Under 'Access time from', select Local system time (or local clock).
  6. In the network adapter selection, choose the physical network card bound to the Terminal Bus.
  7. Click OK.

Step 2: Configure OS Server 2 (Standby Master / Slave)

  1. Open the WinCC project on OS Server 2.
  2. Open the Time Synchronization editor.
  3. Check Synchronization via terminal bus.
  4. Select Take time from a specific computer (Slave mode).
  5. Enter the computer names of both servers: OS_SERVER_1 and OS_SERVER_2.
  6. Configure the network adapter bound to the Terminal Bus.
  7. Enable 'If master fails, take over time master role' if configuring redundant time mastership.

Step 3: Configure OS Clients and Batch Servers

  1. Open the WinCC project for each OS Client and Batch Server.
  2. In the Time Synchronization editor, check Synchronization via terminal bus.
  3. Select Slave -> Take time from a specific computer.
  4. Specify OS_SERVER_1 and OS_SERVER_2 in the server list.
  5. Select the local Terminal Bus network interface.

Step 4: Configure Plant Bus Synchronization in SIMATIC Manager

  1. In SIMATIC Manager, open HW Config for OS Server 1.
  2. Open properties of the CP1623 -> Options tab -> Time-of-day synchronization.
  3. Select Send time-of-day (Active time master on plant bus).
  4. Open HW Config for each AS S7-400 CPU -> Diagnostics/Clock tab.
  5. Under Synchronization, select As slave on the CP443-1 / internal PN interface.
  6. Save, compile, and download HW Config to all stations.

Verification

To confirm system-wide time synchronization:

  1. WinCC TimeSync Diagnostic Log Inspection:
    - On OS Clients and Server 2, open C:\Program Files (x86)\Siemens\WinCC\Diagnose\WinCC_Sys_01.log (or CC_TimeSync.log).
    - Confirm entries: TimeSync: Successfully synchronized with time master OS_SERVER_1.

  2. Clock Alignment Check:
    - Open Windows Command Prompt on OS Server 1, Server 2, Batch Server, and Client.
    - Run time /t simultaneously; verify clocks match to the second.

  3. Alarm Timestamp Test:
    - Trigger a digital input alarm on the AS.
    - Verify in WinCC Alarm Logging that the message timestamp corresponds exactly to the current workstation time.

Limitations and Operational Precautions

Operational limitations and precautions:

  1. Windows Time Service (w32time) Conflict: In workgroups utilizing WinCC TimeSync, the native Windows w32time service must not be configured with conflicting external NTP servers; set w32time to Manual or ensure it does not override WinCC.
  2. No Backward Time Jumps in Runtime: WinCC TimeSync applies clock slew (gradual adjustment) rather than stepping clocks backward, preventing duplicate database archive records.
  3. Broadcast Multicast Filtering: Ensure network switches on the Terminal Bus do not block UDP broadcast/multicast packets used by WinCC TimeSync.
  4. Commercial Disclaimer: Verify all hardware components, communication processors, and system options with an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Can WinCC synchronize time without an external NTP server or domain?

Yes. One OS Server can be designated as the WinCC Time Master, broadcasting its local system time to all other servers and clients across the Terminal Bus.

What is the function of 'Take time from a specific computer' in WinCC?

It configures a station as a Time Slave that listens for broadcast time frames specifically from the designated master server names.

How do S7-400 AS controllers receive time from the OS Server?

The OS Server CP1623 card acts as a Time Master on the Plant Bus, broadcasting SIMATIC time frames to the AS CPUs configured as Time Slaves.

Why shouldn't system clocks jump backwards in WinCC?

Stepping time backward causes duplicate primary keys in Microsoft SQL Server alarm and tag logging databases, corrupting historical archives.

Where can I find diagnostic logs for WinCC time synchronization?

Logs are stored in the WinCC Diagnose directory under C:\Program Files (x86)\Siemens\WinCC\Diagnose\WinCC_Sys_01.log.

Technical References

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Related Tags

  • Time Synchronization
  • WinCC TimeSync
  • Terminal Bus
  • Workgroup Network
  • CP1623 Time Master
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