WinCC RT Archive Variables Exceed 0: Troubleshooting Guide
Quick Answer: When WinCC Runtime (RT) archive variables exceed 0, it typically indicates a configuration mismatch, licensing issue, or communication problem. Check the archive configuration, verify licenses, and ensure proper tag connections.
Understanding WinCC Archive Variables
In Siemens WinCC SCADA systems, archive variables are used to log process data over time. The Runtime (RT) component handles the actual data acquisition and storage. When you see a message indicating that archive variables exceed 0, it often means that the system is trying to archive more variables than allowed by the license, or there is a configuration error preventing proper archiving.
WinCC uses a tag logging system where each variable to be archived must be configured in the Tag Logging editor. The number of archive variables is limited by the installed license (e.g., 128, 512, 1500, or unlimited). Exceeding this limit triggers a system message and stops archiving for some variables.
Common Causes of Archive Variables Exceeding 0
| Cause | Description | Typical Symptom |
|---|---|---|
| License Limit Exceeded | The number of configured archive variables exceeds the license capacity. | System message “Archive variables exceed 0” or similar; some variables not archived. |
| Incorrect Archive Configuration | Archive size, segment settings, or cyclic archive configuration errors. | Data gaps or archive not starting. |
| Communication Failure | Loss of connection to the PLC or data source. | Tags show bad quality; archive variables count may reset. |
| Database Issues | Corrupted SQL server database or insufficient disk space. | Archive errors in WinCC diagnostics. |
| Startup Sequence | Archive system not fully initialized before tags are requested. | Temporary exceed message during startup. |
Step-by-Step Troubleshooting
1. Check the License
Open the WinCC License Manager (or Automation License Manager) and verify the installed license for “WinCC RT Tag Logging”. The license type (e.g., 128, 512, 1500, 65536) determines the maximum number of archive variables. If you have more variables configured than the license allows, you must either reduce the number of archived tags or upgrade the license.
To check the current usage, go to the WinCC Explorer -> Tag Logging -> right-click on the archive and select “Properties”. The number of configured variables is displayed. Compare this with the license limit.
2. Review Archive Configuration
In the Tag Logging editor, ensure that all archive variables are correctly linked to process tags. Look for any variables that might be duplicated or incorrectly configured. Pay attention to the acquisition cycle: a very fast cycle on many variables can overload the system. Consider using a slower cycle for non-critical data.
Also check the archive size and segment settings. If the archive is configured to use a single segment that is too small, it may fill up quickly and cause errors. Use multiple segments with a reasonable size (e.g., 100 MB per segment) and enable automatic segment switching.
3. Diagnose Communication
Use the WinCC Channel Diagnosis tool to check the status of communication drivers. If tags show “bad quality”, the archive system may not count them correctly. Ensure that the PLC is connected and all necessary communication modules are running. Restarting the communication driver or the entire Runtime can sometimes resolve transient issues.
4. Examine the SQL Server Database
WinCC archives data in a Microsoft SQL Server database. Check that the SQL Server instance is running and the WinCC database is not corrupted. Use SQL Server Management Studio to connect to the instance (default: WINCC) and verify the database integrity. Ensure there is sufficient disk space on the drive where the database files are stored.
5. Analyze WinCC Diagnostics
Open the WinCC Diagnostics tool (Start -> Siemens Automation -> WinCC -> WinCC Diagnostics). Look for error messages related to “Tag Logging” or “Archive”. Common errors include “Archive system not ready” or “Cannot write to archive”. These messages often provide specific error codes that can be looked up in the WinCC help system.
Preventive Measures and Best Practices
- Right-size your license: Before project commissioning, accurately estimate the number of archive variables and purchase the appropriate license.
- Optimize acquisition cycles: Use the slowest acceptable cycle for each variable to reduce system load. For example, use 1 second for critical loops and 10 seconds or more for trends.
- Monitor archive usage: Regularly check the number of active archive variables via WinCC scripts or the system diagnostics to catch issues early.
- Implement archive backup: Configure automatic backup of archive segments to prevent data loss and allow for database recovery.
- Test thoroughly: Simulate full load conditions during FAT (Factory Acceptance Test) to ensure the archive system handles all variables without errors.
Pro Tip: Use the WinCC Performance Monitor to track archive system load. If the “Archive Write Queue” consistently grows, consider reducing the number of variables or increasing the acquisition cycle.
Advanced Solutions
If the basic steps do not resolve the issue, consider these advanced approaches:
- Archive splitting: Distribute variables across multiple archives to balance the load and stay within license limits per archive.
- Use of compressed archives: Enable archive compression to save disk space and improve performance (available in newer WinCC versions).
- Script-based monitoring: Write a VBS or C script to periodically check the number of active archive variables and log warnings if approaching the limit.
- Upgrade hardware: If the system is overloaded, consider upgrading the PC hardware (faster CPU, more RAM, SSD for database) to handle the archive load.
Frequently Asked Questions
Q: Can I temporarily increase the archive variable limit?
A: No, the limit is strictly enforced by the license. You must either reduce variables or purchase a larger license. Some trial licenses may offer temporary higher limits.
Q: Does the “exceed 0” message always mean a license issue?
A: Not always. It can also appear during startup before the license is fully checked, or if there is a communication loss causing the system to miscount variables.
Q: How can I see which variables are not being archived?
A: In WinCC Runtime, open the Tag Logging diagnostics or use the “Archive Status” control. Variables that exceed the limit will show a status of “not archived” or “error”.
By following this guide, you should be able to resolve the “archive variables exceed 0” issue in WinCC Runtime and ensure reliable data logging for your SCADA system. Always refer to the official Siemens documentation for version-specific details.
