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Troubleshooting Cyclic Connection Drops Between Redundant OS Servers and Process Historian 2014 SP2

Troubleshooting Cyclic Connection Drops Between Redundant OS Servers and Process Historian 2014 SP2

In SIMATIC PCS 7 long-term archiving systems, when SIMATIC Process Historian (PH) 2014 SP2 exhibits continuous, cyclic connecting and disconnecting states with redundant WinCC OS Servers while basic ICMP ping remains stable and zero telemetry data is logged, the failure is caused by software component version disparities, corrupted 'Processhistorian.cfg' configuration files, or desynchronized Microsoft Message Queuing (MSMQ) queues. This condition typically occurs when the OS Servers run an older PH-Ready component (such as base 2014 or SP1) instead of the matching 2014 SP2 release, when the target OS project properties on the Engineering Station lack the mandatory 'Transfer to external archive server' configuration, or when WinCC server redundancy synchronization is incomplete.

Table of Contents

Process Historian Redundant Pairing and Heartbeat Mechanism

In SIMATIC PCS 7 high-availability architectures, a redundant pair of WinCC OS Servers (OS Server 1 and OS Server 2) streams process values, alarms, and batch data across the terminal bus to a centralized SIMATIC Process Historian (PH):
- Redundancy Protocol: Both OS servers establish independent communication sessions with the Historian via the PH-Ready background component (CCCAPHServer).
- Store-and-Forward: Telemetry is buffered in local Microsoft Message Queuing (MSMQ) queues on each OS server and pushed across TCP port 1801.
- Heartbeat Verification: The PH server continuously monitors session tokens. If an incoming connection handshake violates cryptographic signatures, protocol versions, or project GUIDs, the Historian terminates the TCP connection. The OS Server immediately attempts reconnection, creating an endless connect-disconnect cycle.

Root Causes of Cyclic Connecting-Disconnecting Loops

When the PH Management Console reports flapping connection states:

  1. PH-Ready Version Disparity: The Historian server was upgraded to 2014 SP2, but the WinCC OS Servers still run the legacy 2014 base or 2014 SP1 PH-Ready driver. Handshake packet structures differ between service packs, triggering immediate connection resets.
  2. Missing OS Project Archiving Flags: On the Engineering Station, in the properties of the OS Server project, the checkboxes 'Create/update archive tags' and 'Transfer to external archive server' were not enabled prior to downloading to the OS Servers.
  3. Corrupted Processhistorian.cfg File: During project download from the ES, a configuration file named Processhistorian.cfg is generated in the OS project directory. If this file contains an invalid server name or corrupted GUID, handshake authentication fails.
  4. OS Redundancy Desynchronization: If WinCC Redundancy is actively faulting between OS Server 1 and Server 2 (e.g., both claiming Master status or synchronization incomplete), the Historian rejects the ambiguous data stream.
  5. MSMQ Outgoing Queue Corruption: Corrupted packets in the local MSMQ queue block the pipeline, causing repeated timeout disconnects.

Verifying PH-Ready 2014 SP2 Parity Across All Nodes

Software alignment is mandatory across the entire DCS network:
- On the Process Historian Server: In Windows Control Panel > Installed Software, confirm version: SIMATIC Process Historian 2014 SP2.
- On OS Server 1 and OS Server 2: Confirm version: SIMATIC Process Historian Ready 2014 SP2.
- If the OS Servers display an earlier version, install the matching PH-Ready 2014 SP2 update from the PCS 7 installation media immediately.

Step-by-Step Diagnostic and Recovery Sequence

Execute the following recovery procedure to stabilize communication:

Step 1: Verify OS Project Configuration on ES

  1. On the Engineering Station, open SIMATIC Manager.
  2. Right-click the OS Server object and select Object Properties.
  3. Switch to the Target OS and Standby OS Computer tab.
  4. Verify that the following options are checked:
    - [x] Create/update archive tags
    - [x] Transfer to external archive server
  5. Click OK and perform a full OS project download to both servers.

Step 2: Validate Processhistorian.cfg on OS Servers

  1. On OS Server 1 and Server 2, navigate to the WinCC project directory:
    D:\SIEMENS\STEP7\S7Proj\<Project_Name>\wincproj\<OS_Name>\
  2. Confirm that the file Processhistorian.cfg exists.
  3. Open the file in Notepad; verify that the ServerName matches the exact NetBIOS name of the Process Historian server.

Step 3: Clear MSMQ Outgoing Queues

  1. Deactivate WinCC Runtime on OS Server 2 (Standby).
  2. On OS Server 2, open Computer Management > Services and Applications > Message Queuing > Outgoing Queues.
  3. If the queue targeting the PH server is paused or reports status 'Inactive', right-click and select Purge.
  4. Restart the CCCAPHServer service in services.msc.
  5. Repeat the purge on OS Server 1.

Step 4: Staged Activation and Redundancy Verification

  1. Activate WinCC Runtime on OS Server 1 (Master). Wait for the runtime to fully initialize.
  2. Open the PH Management Console on the Historian; confirm that the connection count increases to 1 and status stabilizes as Connected.
  3. Activate WinCC Runtime on OS Server 2 (Standby). Wait for server synchronization to finish (verify @RedundancyState = 1).
  4. Confirm that the connection count in PH Management Console increases to 2 and data throughput graphs begin logging data.

Diagnostic Matrix for Process Historian Pairing States

The table below outlines pairing states and corrective actions:

Connection StatePing StatusUnderlying CauseCorrective ActionCyclic Connect/DisconnectConstant OKPH-Ready version mismatch or Processhistorian.cfg errorInstall PH-Ready 2014 SP2; check ES project propertiesDisconnected (Permanent)Request Timed OutPhysical network disconnect or firewall blocking port 1801Open TCP port 1801 and 135; check terminal bus cablesConnected, 0 Data StoredConstant OKTags not configured for long-term archivingEnable 'Archive' property on tags; compile OSOnly 1 Server ConnectsConstant OKStandby server project not synchronizedCheck WinCC Redundancy synchronization state

Verification

To confirm that cyclic connection drops are resolved:
1. PH Management Console Stability Check: Monitor the PH Management Console for 30 minutes; verify that the connection status for both OS servers remains solidly Connected with zero disconnect events.
2. Data Throughput Verification: Verify that the Lower Graph (received data volume) displays continuous activity spikes.
3. Historical Trend Validation: Open a trend screen in WinCC Runtime; request historical data; confirm that long-term tags load without latency.

Limitations and Operational Precautions

Engineering teams must observe the following precautions:
- Never install different service pack levels between Process Historian and PH-Ready components across the plant network.
- Purging MSMQ queues removes uncommitted data buffered during the outage; perform only when recovering from severe communication deadlock.
- Always validate final license quantities and MLFBs against the applicable Siemens catalog and authorized distributor quotation when procuring Process Historian packages.

Engineer FAQ

Where can I find the communication error logs for PH-Ready?

On the OS Server, inspect the log files in C:\ProgramData\Siemens\ProcessHistorian\LogFiles\ or C:\Program Files (x86)\Siemens\WinCC\diagnose\.

Does restarting Process Historian cause data loss on the OS?

No. While Process Historian is restarting, the PH-Ready component automatically buffers process tags and alarms in local MSMQ queues, transmitting them upon reconnection.

Can Process Historian 2014 SP2 connect to PCS 7 v9.0 systems?

No. Process Historian 2014 SP2 is certified for PCS 7 v8.1 and v8.2. PCS 7 v9.0 requires Process Historian 2017.

Technical References

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Related Tags

  • Process Historian
  • PH 2014 SP2
  • WinCC Redundancy
  • MSMQ
  • Connection Drops
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