C135 PCS 7 (PCS7)
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Monitoring Connected Clients and Active Tag Counts in SIMATIC PCS 7 OPC DA Servers

Monitoring Connected Clients and Active Tag Counts in SIMATIC PCS 7 OPC DA Servers

To monitor the number of active clients connected to an OPC DA or OpenPCS 7 server in SIMATIC PCS 7, utilize the WinCC Channel Diagnosis utility (WinCCChannelDiagnosis.exe) located under WinCC Explorer -> Tools -> Channel Diagnosis, or inspect the dedicated performance counters in Windows Performance Monitor (perfmon.msc) under the 'SIMATIC NET OPC Server' or 'WinCC OPC Server' category. To verify the total number of registered process tags, inspect the Tag Management status bar in WinCC Explorer, view the 'Total Items' counter in perfmon, or browse the OPC address space using Siemens OPC Scout V10.

Table of Contents

Executive Summary

In enterprise process architectures where SIMATIC PCS 7 V9.0 exchanges operational data with third-party SCADA, historians, or Manufacturing Execution Systems (MES) via OPC Data Access (OPC DA) or OpenPCS 7, system administrators must actively monitor communication loads. Unchecked client connections, excessive polling rates, and ballooning tag subscriptions can consume server memory and CPU threads, degrading WinCC OS runtime responsiveness. Engineers frequently struggle to find real-time diagnostic metrics detailing how many external OPC client sessions are actively bound to the server and how many tags are currently registered. Leveraging the integrated WinCC Channel Diagnosis tool, Windows Performance Monitor counters, and OPC Scout provides complete diagnostic transparency.

Architecture and Fundamental Mechanics

The diagnostic infrastructure for OPC communication in SIMATIC PCS 7 operates across multiple layers:

1. The WinCC Channel Diagnosis Engine

The WinCC runtime communications engine hosts the utility WinCCChannelDiagnosis.exe:
- It provides a real-time graphical dashboard monitoring all active communication drivers (Named Connections, OPC.chn, OpenPCS 7).
- Under the OPC or OpenPCS 7 driver tab, it displays the operational state of the channel (State: OK / Ready), the number of active logical connections, and the error counters for read/write requests.

2. Windows Performance Monitor Counters (perfmon)

During software installation, SIMATIC NET and WinCC register custom Performance Counter objects with the Windows kernel:
- Object: SIMATIC NET OPC Server / WinCC OPC DA Server
- Connected Clients: Displays an instantaneous integer count of all DCOM client applications holding an open interface pointer.
- Active Items / Total Tags: Quantifies the exact number of process variables currently subscribed in active group update cycles.
- Transactions / sec: Displays the throughput rate of synchronous and asynchronous data callbacks.

3. OpenPCS 7 and OPC UA Session Diagnostics

If OpenPCS 7 or native OPC UA is utilized, session diagnostics are embedded directly into the OPC address space:
- The root node Server -> ServerDiagnostics exposes standard UA diagnostic variables:
- CurrentSessionCount: Real-time count of active client sessions.
- CurrentSubscriptionCount: Total active data subscription monitoring groups.

Step-by-Step Implementation Procedure

To monitor active client sessions and tag counts in real time:

Method 1: Using WinCC Channel Diagnosis

  1. On the active OS Server or OpenPCS 7 station, open WinCC Explorer.
  2. In the menu, click Tools -> Channel Diagnosis (or launch C:\Program Files (x86)\Siemens\WinCC\bin\WinCCChannelDiagnosis.exe).
  3. In the Channel Diagnosis window, click on the Channels/Connections tab.
  4. Expand the OPC or OpenPCS 7 channel unit.
  5. Review the connection list: each connected client node is listed with its network identifier, connection status (green checkmark), and communication counters.

Method 2: Using Windows Performance Monitor (perfmon)

  1. Press Windows Key + R, type perfmon.msc, and press Enter.
  2. In Performance Monitor, click on Performance Monitor under Monitoring Tools.
  3. Click the green Add (+) button on the toolbar.
  4. In the Available Counters list, locate SIMATIC NET OPC Server or WinCC OPC.
  5. Select the counters:
    - Clients Connected
    - Active Items
    - Item Count
  6. Click Add >> and then OK.
  7. Switch the display to Report view (Ctrl+R) to view live numerical counts.

Method 3: Using Siemens OPC Scout V10

  1. Launch OPC Scout V10 from the Siemens SIMATIC menu.
  2. Expand Local COM/DCOM -> OPC.SimaticNET or PCS7.OPCDAServer.
  3. Connect to the server; navigate to the Server Status diagnostic window.
  4. Review the server state, startup timestamp, group count, and total items.

Verification

To verify diagnostic tracking accuracy:

  1. Client Connection Test:
    - Connect an external OPC test client (e.g., Matrikon OPC Explorer or third-party MES).
    - Verify in perfmon that Clients Connected immediately increments from $N$ to $N+1$.

  2. Subscription Tag Count Test:
    - Add a group of 50 process tags into the client's subscription list.
    - Confirm that Active Items in Performance Monitor reflects the addition of exactly 50 tags.

  3. Disconnect Test:
    - Close the test client; confirm that the connection counter drops back and resources are cleanly deallocated.

Limitations and Operational Precautions

Operational limitations and precautions:

  1. DCOM Timeout Latency: With classical OPC DA, ungraceful client disconnections (e.g., process crashes or cable pulls) may take up to 6 minutes for Windows DCOM RPC timeouts to decrement the connected client count.
  2. Process Object (PO) Tag Limits: High tag counts accessed via OPC count toward the licensed WinCC OS Runtime Process Objects (PO) or tag tiers; excessive unregistered tags can trip license violations.
  3. OpenPCS 7 Dedicated Node: For high tag counts (> 5000 tags polling at 1-second intervals), Siemens strongly mandates hosting OpenPCS 7 on a dedicated standalone PC to isolate OS Server runtime.
  4. Commercial Disclaimer: Verify all software options, OpenPCS 7 licenses, and server capacity limits with an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Where can I see the number of connected OPC clients in WinCC?

Use the WinCC Channel Diagnosis tool (WinCCChannelDiagnosis.exe) or Windows Performance Monitor (perfmon.msc) under the SIMATIC NET OPC Server counter.

How do I determine the total number of tags registered in the OPC server?

In Windows Performance Monitor, inspect the Item Count or Active Items counter, or browse tag totals in WinCC Tag Management.

Why does the client count stay high after an external OPC client crashes?

Classical OPC DA relies on Microsoft DCOM. If a client terminates ungracefully, DCOM retains the connection handle until the RPC ping timeout (typically 6 to 9 minutes) expires.

Can I monitor OPC UA client connections directly inside the address space?

Yes. Standard OPC UA servers expose dynamic diagnostic tags under Server -> ServerDiagnostics -> CurrentSessionCount.

What is the tool WinCCChannelDiagnosis.exe used for?

It is a built-in Siemens diagnostic application that monitors active communication channels, connection quality, and packet errors in real time.

Technical References

Related Articles

Related Tags

  • OPC DA Server
  • WinCC Diagnostics
  • OpenPCS 7
  • Performance Monitor
  • Client Connections
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