Implementing GPS and NTP Master Time Synchronization in PCS 7 Following SICLOCK Discontinuation

Following the manufacturer phase-out and discontinuation of the Siemens SICLOCK time server portfolio (such as SICLOCK TC100, TC400, and SICLOCK GPS), plant-wide master GPS and NTP time synchronization in SIMATIC PCS 7 is implemented using certified third-party time servers from Bürk Mobatime (such as Mobatime DTS 4128, DTS 4138, or Grandmaster DTS 4210). Siemens tested and officially certified Bürk Mobatime time servers for complete compatibility within the PCS 7 environment. In the plant network architecture, the GPS time server operates as an external Network Time Protocol (NTP) master connected to the Plant Bus and Terminal Bus, broadcasting synchronized UTC time telegrams to the CP 443-1 / CPU 410-5H controllers, OS Servers, and OS Clients down to millisecond accuracy.

Executive Summary

High-integrity sequence-of-events (SOE) recording, alarm logging, and historical batch tracking in SIMATIC PCS 7 require absolute, plant-wide time synchronization across all distributed controllers, operator servers, and client consoles. Historically, Siemens facilities standardized on the SICLOCK product family to synchronize system clocks to GPS satellites. With SICLOCK officially phased out, engineering teams seeking replacement GPS master clocks must adopt Siemens' certified successor technology. In formal collaboration with Siemens, time servers from Bürk Mobatime have been validated for seamless integration into PCS 7 architectures, ensuring continuous millisecond-accurate time stamping without software modification.

Architecture and Fundamental Mechanics

The master time synchronization architecture in SIMATIC PCS 7 is organized hierarchically to eliminate clock drift across the DCS:

The SICLOCK Phase-Out and Successor Certification:
* Siemens announced the comprehensive product phase-out of the SICLOCK product line (SICLOCK TC100/TC400, SICLOCK GPS decoders, and pulse converters).
* To provide industrial continuity, Siemens partnered with Bürk Mobatime, conducting rigorous compatibility testing of Mobatime's Distributed Time System (DTS) devices in PCS 7 test labs.
* Bürk Mobatime servers (e.g., DTS 4128.sys, DTS 4138.sys) provide identical NTP and SIMATIC time telegram capabilities matching SICLOCK functionality.
Network Topology of GPS Time Synchronization:
* Level 1 (Time Source): A GPS / GLONASS antenna mounted on the plant roof connects via coaxial cable to the Mobatime time server in the central control room cabinet.
* Level 2 (Time Master Server): The Mobatime server decodes the atomic satellite signal, maintains internal oven-controlled crystal oscillator (OCXO) stability during satellite loss, and acts as an NTP Stratum 1 Time Server.
* Level 3 (Plant Bus & Controllers):
- The time server connects directly to the Industrial Ethernet Plant Bus via SCALANCE switches.
- It broadcasts NTP packets (UDP port 123) or SIMATIC time telegrams.
- S7-400 / CPU 410-5H controllers (via CP 443-1 or onboard PROFINET) receive the NTP broadcast, updating the AS system clock in UTC.
- Level 4 (Terminal Bus & WinCC OS):
- WinCC OS Servers synchronize their Windows system clocks to the Mobatime NTP server using the Windows Time service (w32time) or WinCC Time Synchronization editor.
- The primary OS Server then synchronizes OS Clients via the WinCC Terminal Bus time master protocol.

Step-by-Step Implementation Procedure

Follow these procedures to configure GPS/NTP time synchronization using a Mobatime server in PCS 7:

Hardware Installation and Network Interfacing:
* Install the Bürk Mobatime time server (e.g., DTS 4128) into the central 19-inch cabinet.
* Connect the GPS antenna cable to the RF input; verify satellite lock on the server's front display.
* Connect LAN Port 1 to the PCS 7 Plant Bus network switch.
* Connect LAN Port 2 (if equipped) to the Terminal Bus network switch for physical segregation.
* Configure the time server with static IP addresses matching the plant subnets (e.g., Plant Bus: 192.168.0.250, Terminal Bus: 192.168.1.250).
* Enable NTP Service on both network ports; ensure UTC time zone is selected.
Configure AS Controller Time Synchronization in HW Config:
* Open HW Config for the S7-400 / CPU 410-5H station in SIMATIC Manager.
* Double-click the Industrial Ethernet interface (CP 443-1 or CPU onboard PN-IO).
* Navigate to the Time-of-Day Synchronization tab.
* Check the box Enable time-of-day synchronization in NTP mode.
* In the NTP Server table, click Add and enter the Mobatime server's IP address (e.g., 192.168.0.250).
* Set the synchronization interval (e.g., 10 seconds).
* Check Keep alive; save and compile HW Config.
Configure CPU Clock Parameters:
* In HW Config, double-click the CPU module and navigate to the Diagnostics/Clock tab.
* Under Synchronization, set On MPI/DP: None (or Master if synchronizing ET 200 distributed racks).
* Set On backplane bus (K-bus): As slave (to receive time from the CP 443-1).
* Save and compile; download hardware configuration to the AS.
Configure WinCC OS Server Time Synchronization:
* Open the OS project in WinCC Explorer.
* Double-click Time Synchronization.
* Check Synchronization via system bus (Master, Slave).
* Under 'Access point', select the network card connected to the terminal bus or plant bus.
* Alternatively, configure Windows Time (w32time) to synchronize with the Mobatime NTP server:
- Open Command Prompt as Administrator and run:
  w32tm /config /manualpeerlist:"192.168.1.250" /syncfromflags:manual /reliable:YES /update
  w32tm /resync
- In WinCC Time Synchronization editor, configure the primary OS Server as the Time Master for Terminal Bus to synchronize all connected OS Clients.

Verification

Inspect the front panel of the Mobatime time server; verify that satellite tracking indicates >= 4 synchronized satellites. In SIMATIC Manager, select the CPU and execute PLC > Set Time of Day; confirm that the CPU module time reflects exact UTC time synchronized with the satellite clock without drifting. In WinCC Runtime, open the alarm list; generate a test alarm and confirm that the timestamp matches atomic time to millisecond resolution.

Limitations and Operational Precautions

Always maintain the AS controller operating system clock in Coordinated Universal Time (UTC), never local daylight-saving time. WinCC automatically translates UTC controller timestamps into local workstation time for display. Setting a controller to local time causes negative time jumps during daylight saving transitions, corrupting alarm logging databases.

Engineer FAQ

Why did Siemens discontinue the SICLOCK product line?

Siemens streamlined its portfolio to focus on core automation, certifying specialized industrial time synchronization leaders like Bürk Mobatime to provide modern, high-precision GPS/NTP appliances.

Does Mobatime require special software in PCS 7?

No. Mobatime servers use standard IEEE Network Time Protocol (NTP) and standard SIMATIC time broadcast telegrams, requiring zero custom software in PCS 7.

What happens if the GPS antenna cable is cut?

Mobatime time servers feature high-stability internal quartz or rubidium oscillators that maintain microsecond-level holdover accuracy for days until satellite tracking is restored.

Can a single time server synchronize both redundant OS servers and redundant AS controllers?

Yes. Multi-port time servers (like Mobatime DTS 4138) feature independent physical Ethernet interfaces that can synchronize both the Plant Bus and Terminal Bus simultaneously without routing between them.