C135 PCS 7 (PCS7)
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Resolving WinCC OS Delta Download Invalidation - Exceeded Recommended Amount of Changes

Resolving WinCC OS Delta Download Invalidation - Exceeded Recommended Amount of Changes

In SIMATIC PCS 7 V9.0 (SP1, SP2, SP3), the error 'The recommended amount of changes has been surpassed to guarantee changes download' (Die empfohlene Änderungsmenge wurde überschritten) disables the 'Changes Only' download option and forces a full OS download because the working delta loader status file enforces an obsolete 1,000-tag limit. In modern APL projects, instantiating just 10 PID loops exceeds 1,000 tags. Although WinCC increased this threshold to 10,000 tags in newer updates (defined in dlStatusConfig.xml), existing installations retain an active working copy named dlStatusConfigCurrent.xml that remains locked to 1,000 tags. To restore delta downloads: delete dlStatusConfigCurrent.xml from C:\Users\Public\Documents\Siemens\WinCC, recompile the OS, and trigger the delta download.

Table of Contents

Executive Summary

During plant expansions or routine online commissioning on operating SIMATIC PCS 7 systems, the ability to download incremental changes ('Changes Only') from the Engineering Station to redundant OS Servers without stopping runtime is essential for continuous process uptime. Engineers frequently encounter an unexpected barrier where the 'Changes' radio button in the OS download dialog becomes disabled, accompanied by a warning that the recommended change volume has been exceeded. This occurs even when the actual change set comprises only a handful of technological blocks. This guide analyzes the internal limits of the WinCC Online Delta Loader, explains why update installations fail to purge legacy limit files, and provides the verified workaround to raise the threshold to 10,000 tags.

Architecture and Fundamental Mechanics

WinCC Online Delta Loader Limit Mechanics

+-------------------------------------------------------------------------+
|                        SIMATIC PCS 7 Engineering Station                |
|                                                                         |
|   [Engineer adds 12 PIDConL Blocks in CFC -> AS-OS Compile]             |
|   - 12 Blocks x ~100 Tags/Block = ~1,200 New WinCC Tag Records          |
+-----------------------------------|-------------------------------------+
                                    |
                                    v Delta Loader Evaluation
+-------------------------------------------------------------------------+
|            WinCC Delta Loader Configuration File Inspection             |
|                                                                         |
|   Location: C:\Users\Public\Documents\Siemens\WinCC\                    |
|                                                                         |
|   Master Template:  dlStatusConfig.xml         [Limit: 10,000 Tags]     |
|   Active Copy:      dlStatusConfigCurrent.xml  [Limit:  1,000 Tags] <--!|
+-----------------------------------|-------------------------------------+
                                    |
         +--------------------------+--------------------------+
         |                                                     |
         v Comparison Check                                    v Workaround Action
+------------------------------------+           +------------------------+
| 1,200 Tags > 1,000 Tag Limit       |           | DELETE ACTIVE FILE:    |
|                                    |           | dlStatusConfigCurrent  |
| -> Delta Download DISABLED!        |           |                        |
| -> System demands FULL DOWNLOAD    |           | Next compile creates   |
|    which halts running OS Runtime! |           | fresh copy with        |
|                                    |           | 10,000 TAG LIMIT!      |
+------------------------------------+           +------------------------+

The Software Update Anomaly

  1. APL Tag Volume: Classical PCS 7 blocks required 10–20 tags each. Modern Advanced Process Library (APL) blocks—such as PIDConL, MotSpdCL, and VlvAnL—utilize structured variables, signal status bytes, and auxiliary attributes generating over 100 WinCC tag management records per block instance.
  2. The 1,000-Tag Bottleneck: WinCC historically restricted delta downloads to 1,000 tag records to prevent excessive lockup of the SQL runtime database during online injection.
  3. Failure of Update Installers to Delete Working Copies: When Siemens released WinCC V7.4.1.10 / PCS 7 V9.0 SP2 raising the limit to 10,000 tags, the installer updated dlStatusConfig.xml. However, if the project had already performed a delta download prior to the update, the working copy dlStatusConfigCurrent.xml was left untouched in the Public Documents folder, indefinitely enforcing the old 1,000 tag restriction.

Step-by-Step Implementation Procedure

Step 1: Locate and Delete the Obsolete Working File

  1. On the Engineering Station (and target OS Servers if performing local maintenance), open Windows Explorer.
  2. Navigate to the Public Documents folder:
    - English OS: C:\Users\Public\Documents\Siemens\WinCC
    - German OS: C:\Benutzer\Öffentlich\Öffentliche Dokumente\Siemens\WinCC
  3. Locate the active working configuration file: dlStatusConfigCurrent.xml.
  4. DELETE the file dlStatusConfigCurrent.xml (or rename it to dlStatusConfigCurrent.xml.bak).
  5. Do NOT delete the master template file dlStatusConfig.xml.

Step 2: Verify Master Configuration Limit in dlStatusConfig.xml

  1. In the same folder, right-click dlStatusConfig.xml and open with Notepad.
  2. Search for the tag limit entry (e.g., <MaxTags> or <TagManagementLimit>).
  3. Verify that the configured value is set to 10000.
  4. If the value is still 1000, update the value to 10000, save, and close the file.

Step 3: Recompile the OS in SIMATIC Manager

  1. Return to SIMATIC Manager on the Engineering Station.
  2. Right-click the OS project and select Compile.
  3. Choose Scope: Changes only and complete the compilation.
  4. During compilation, the WinCC Delta Loader reads dlStatusConfig.xml and generates a fresh, updated dlStatusConfigCurrent.xml with the expanded 10,000-tag limit.

Step 4: Execute Delta Download to Redundant Servers in Correct Sequence

  1. Open the OS Download dialog in SIMATIC Manager.
  2. Confirm that the Scope: Changes radio button is now re-enabled and selectable.
  3. In redundant configurations, always follow the recommended sequence (Compendium Part A):
    - Download changes first to the Standby OS Server.
    - Verify redundancy synchronization completes.
    - Download changes to the Master OS Server.

Verification

  1. File Regeneration Check: Inspect C:\Users\Public\Documents\Siemens\WinCC. Confirm that a newly created dlStatusConfigCurrent.xml exists with a recent timestamp.
  2. Download Execution: Perform the delta download. Verify that the progress bar executes online injection of tags and graphics without error, terminating with: Download of changes to OS completed successfully.
  3. Runtime Continuity: Confirm that WinCC Runtime on both OS servers remained in active operation without restarting SQL Server or disconnecting client stations.

Limitations and Operational Precautions

  1. Structural Alterations Require Full Download: Deleting dlStatusConfigCurrent.xml resolves tag quantity limits, but structural modifications—such as renaming the OS project, altering archive acquisition time bases, or changing WinCC User Archive database schemas—cannot be loaded via delta download and legitimately require an Entire Download.
  2. Redundant Synchronization Prerequisite: If the redundant partner server is offline or desynchronized, SIMATIC Manager will block delta download until server pairing is restored.

Engineer FAQ

Why did the download dialog say the recommended amount of changes was surpassed?

The working configuration file dlStatusConfigCurrent.xml was enforcing an obsolete 1,000-tag limit from an earlier WinCC version.

Where is dlStatusConfigCurrent.xml located?

In C:\Users\Public\Documents\Siemens\WinCC (or C:\Benutzer\Öffentlich\Öffentliche Dokumente\Siemens\WinCC).

Does deleting dlStatusConfigCurrent.xml cause data loss?

No. It is a temporary working snapshot; WinCC automatically regenerates it from dlStatusConfig.xml upon the next compile.

What is the expanded tag limit in modern PCS 7 versions?

10,000 tags, starting in WinCC V7.4.1.10 and PCS 7 V9.0 SP2/SP3.

Why does adding only 10 PID blocks exceed 1,000 tags?

Each APL PIDConL block instantiates approximately 100 to 110 WinCC tag records, including setpoints, feedbacks, limits, and status bytes.

Why didn't the PCS 7 SP2 update fix this automatically?

The update installer updates dlStatusConfig.xml but does not delete previously created dlStatusConfigCurrent.xml files.

Can I set the tag limit higher than 10,000?

It is not recommended by Siemens, as injecting more than 10,000 tags online can cause severe SQL locking and freeze runtime graphics.

In what order should redundant servers be downloaded?

Download changes to the Standby OS Server first, verify synchronization, and then download to the Master OS Server.

What if deleting the file does not enable delta download?

If the change set contains structural database alterations (archive cycle changes, project renaming), a full download is mandatory.

Does this file exist on OS Clients?

No, the delta loader configuration is evaluated on the Engineering Station and OS Servers.

Technical References

Related Articles

Related Tags

  • Delta Download
  • dlStatusConfig.xml
  • OS Download
  • WinCC V7.4
  • PCS 7 V9.0 SP3
  • Redundant OS
  • Changes Only
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