Troubleshooting DataMonitor Archive Discrepancies and Report Anomalies in PCS 7

Discrepant trend curves or unexpected calculation results in WinCC DataMonitor reports typically stem from mismatched time zone synchronization, improper archive tag compression cycles, or incorrect aggregate function selections (e.g., using 'Interpolated' rather than 'Time-Weighted Average'). To resolve this, verify that the OS Server and DataMonitor web server share identical UTC time synchronization, configure Tag Logging to retain uncompressed raw samples for critical regulatory tags, and select the appropriate statistical aggregation function in the DataMonitor Excel Workbook wizard.

Executive Summary

SIMATIC WinCC DataMonitor is a web-based corporate reporting and visualization tool used by plant managers and process engineers to inspect WinCC Runtime archives, generate scheduled Excel reports, and display process dashboards over standard office LANs. When DataMonitor generates values that diverge from live WinCC Runtime trends—such as truncated peak values, missing intervals, or timestamp offsets—engineers often suspect database corruption. This article explains how DataMonitor extracts and aggregates Tag Logging data, the impact of time zones and compression, and how to configure accurate reporting.

Architecture and Fundamental Mechanics

DataMonitor Data Extraction and Aggregation Mechanics:

Architecture of WinCC DataMonitor:
DataMonitor functions as a web server querying the local WinCC Tag Logging / Alarm Logging SQL databases or the central Process Historian.
Client tools include WebCenter (browser dashboards) and Excel Workbooks (automated spreadsheet reporting).
The Role of Compression and Aggregation Functions:
If WinCC Tag Logging is configured with archive compression (e.g., swinging door or delta compression), intermediate values are discarded to conserve disk space.
When DataMonitor requests data over an interval (e.g., hourly averages), it evaluates the available samples using SQL aggregate functions:
- AVERAGE: Arithmetic mean of stored points (can be misleading if points are logged on-change).
- TIME-WEIGHTED AVERAGE: Correct calculation for process variables with uneven time spacing.
- INTERPOLATED: Estimates values at specific time stamps via linear regression.
Time Zone Handling:
WinCC stores all historical timestamps in Coordinated Universal Time (UTC).
DataMonitor converts UTC into the web browser client's local time zone. If Daylight Saving Time (DST) offsets or server time configurations differ, 1-hour shifts or 'weird' zero-interval duplicates occur.

Step-by-Step Implementation Procedure

Troubleshooting Workflow for DataMonitor Archive Discrepancies:

Audit Server and Client Time Synchronization:
- Verify that the WinCC OS Server, DataMonitor web server, and client PCs synchronize to the central NTP master clock.
- Confirm that Windows Time Zone and Daylight Saving Time settings match across all participating workstations.
Verify Tag Logging Archive Settings in WinCC Explorer:
- Open WinCC Explorer on the OS Server -> Tag Logging.
- Open properties for the problematic archive tag.
- Inspect acquisition type: if using 'Cyclic, continuous', confirm the cycle interval (e.g., 1s, 5s).
- If compression is enabled, ensure the deadband threshold is not set so high that real process peaks are filtered out.
Configure DataMonitor Excel Workbook Aggregation Query:
- In Microsoft Excel, open the DataMonitor tab -> 'Insert Tag Values'.
- In the Query wizard -> 'Time interval' tab, specify start/end times.
- Under 'Calculation mode', select Time-weighted average (for continuous analog tags) or Actual value (for raw unaggregated samples).
Validate Database Consistency via SQL Query:
- Using SQL Server Management Studio (SSMS) on the OS Server, query the WinCC archive view directly (TAG:R,...); compare raw SQL values against the DataMonitor output.
Re-Publish DataMonitor WebCenter Reports:
- In the DataMonitor administrator console, refresh the web report cache and verify that published graphs match runtime trends.

Verification

To verify DataMonitor report accuracy:
1. Generate an automated DataMonitor report covering a 24-hour production shift.
2. Open the WinCC OnlineTrendControl on an OS Client covering the identical 24-hour period.
3. Compare peak values, minimums, and totalized batch volumes; confirm that values align within <0.1% margin of calculation.

Limitations and Operational Precautions

Operational precautions:
- Querying large time ranges of raw, unaggregated high-speed data (>100,000 points) via DataMonitor during active production can place heavy CPU loads on the OS Server; use time-weighted aggregates for multi-month reports.
- Ensure that DataMonitor client licenses (DataMonitor 1, 3, or 10 client connections) are installed in ALM on the web server.
- Do not alter WinCC SQL database tables directly via standard SQL insert/delete commands.

Engineer FAQ

Why do DataMonitor trends show a 1-hour time offset compared to WinCC?

Because WinCC stores data in UTC time, and the client browser or web server has an incorrect local time zone or Daylight Saving Time configuration.

What aggregation function should be used for on-change archived tags?

Always use 'Time-Weighted Average' rather than simple arithmetic average for on-change or unevenly sampled tags.

Does DataMonitor query the PLC directly?

No. DataMonitor queries the WinCC Tag Logging / Alarm Logging SQL databases or the Process Historian.

Why are process peaks missing in DataMonitor Excel reports?

Because the query was configured with an aggregate function (e.g., 1-hour average) that smooths out brief spikes, or Tag Logging compression filtered out the peak.

What software license is required for WinCC DataMonitor?

WinCC DataMonitor Server base license plus client access licenses (CALs) installed in Automation License Manager.

Technical References

Related Tags

DataMonitor
Tag Logging
Time Synchronization
Excel Reporting
Process Historian

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Troubleshooting DataMonitor Archive Discrepancies and Report Anomalies in PCS 7