Troubleshoot Missing Analog Trend History in CEMAT CS

When CEMAT CS no longer displays historical analog values, first determine whether the problem is the trend display or the underlying archived data. CEMAT TrendControls can display archived process-value tags as well as online process tags, so check the selected data source and time range, then verify that the relevant archive contains values for that period. The report gives no software version, screenshot, tag name or archive status, so it does not establish a specific cause or a confirmed fix.

Symptoms and Interpretation

The reported symptom affects trend history for analog values that previously displayed. The discussion contains no screenshot or information about whether current live values still appear, whether all archived history is absent, or whether only one screen/time range is affected. Siemens' CEMAT V9.1 system description says TrendControls can display archived values from the process-value archive and online process-tag values from tag management. A missing historical curve therefore needs separate checks for the view's data link/time selection and the archive data itself. This is a diagnostic distinction, not a confirmed cause for the reported system.

Establish the Scope of the Failure

Capture the affected trend screen, including the visible time interval, tag name, scale and any trend-control status. Record the exact CEMAT, PCS 7 and WinCC versions and updates.
Check whether the analog tag's current value is visible in its faceplate or another established online display. If live values are also missing, investigate the process-tag/communication path separately from history.
Compare more than one affected tag and trend. If all historical trends fail together, prioritize shared archive/runtime or data-source configuration; if only one fails, compare that tag's archive assignment and trend link with a working tag. This comparison is a diagnostic method, not a claim about the root cause.
Record the selected time range and whether the trend uses archived tags or online process tags. Avoid changing archive configuration while collecting evidence.

Check the Trend Data Source and Time Range

CEMAT TrendControls can be configured to display archive tags or online process tags, and the time window can be specified using start/end times, a start time and period, or a start time and number of measurement points. In the affected trend's documented CEMAT/WinCC configuration, confirm that the intended archive tag is linked, that the requested start and end fall within the period for which data exists, and that the displayed range is not simply outside the archived interval. CEMAT's V8.2 reference manual describes WinCC OnlineTrendControl navigation, including first/previous/next/last archived data records; availability and control behavior depend on the configured control and version. Use the matching installed version's help rather than assuming the same toolbar layout.

Check Whether the Archive Contains Values

In the installed WinCC Tag Logging/Process Value Archive configuration, verify that the affected process tag is actually assigned to the archive used by the trend and that archive logging is active for the relevant period. Compare its archive assignment and data availability with a known working analog tag. Determine whether the expected period is in the active archive or was moved/swapped to another storage location; do not relocate or attach archive data without the corresponding version-specific Siemens procedure and a backup. A trend control cannot render historic samples that are not available through its configured archive source.

Apply Version-Specific Checks

The source does not identify its WinCC version. If the installation is WinCC V7.4 SP1 and the data is in swapped-out archive segments, Siemens' Update 18 Readme specifically lists an improvement for display of swapped-out archive values in WinCC OnlineTrendControl. Treat this only as a version-specific check: verify the installed update level and release notes before considering an update, and follow the site's validated patch/change procedure. It does not prove that swapped-out data caused this incident or that Update 18 applies to another WinCC release.

Verification

After identifying and correcting a documented mismatch, select a time interval known to contain archived samples and confirm the historical curve appears for more than one expected timestamp. Check the tag identity, value/time relationship and archive source, and compare against an independent archive readout or another established display where available. Confirm that current online values still behave as expected and that the history remains accessible after normal screen navigation. Record the exact version, time interval and observed result; do not claim a test occurred unless one was performed on the plant.

Limitations and Operational Precautions

No cause or resolution is present in the discussion; the only reply requests a screenshot. The CEMAT documentation cited here describes trend features, not the state of this installation's archives. The system versions, affected trend configuration and archive status are unknown. Do not delete, reset, reconfigure, move or restore archive segments as an exploratory step. Protect archived process data, preserve a backup and coordinate any archive/runtime or software change with operations and the site's change-control process.

Engineer FAQ

What should I check first when live values appear but history does not? Check that the trend is linked to the intended archive tag and that its requested time interval overlaps available archived samples.

Can a CEMAT TrendControl show online values and archived values? Siemens' CEMAT V9.1 system description documents both sources: online process tags and archived process-value tags.

Could the displayed time range explain a blank curve? Yes, if the selected interval does not overlap available archived values. Confirm the range and archive time coverage before changing logging configuration.

What does an Update 18 reference mean? Siemens lists a WinCC V7.4 SP1 Update 18 improvement for displaying swapped-out archive values. It is relevant only to that version/update context and does not diagnose this report.

What evidence should be sent to support? Provide a redacted screenshot, exact CEMAT/PCS 7/WinCC versions and updates, affected tag/archive names, selected interval, whether online values work, and whether the archive contains data for that period.

Technical References

Siemens, CEMAT V9.1 Reference Manual System, function manual, 11/2020, A5E50300953-AA, TrendControls: archived process-value archive tags, online process tags and selectable time ranges: https://support.industry.siemens.com/cs/attachments/109798210/Cem_V91_System_000_en.pdf
Siemens, CEMAT V8.2 Reference Manual System MinAS, OnlineTrendControl toolbar and archived-record navigation: https://support.industry.siemens.com/cs/attachments/109745916/Cem_V82_System_001_en.pdf
Siemens, WinCC V7.4 SP1 Update 18 Readme, A5E41459682-AT, 06/2021, Tag Logging improvement for display of swapped-out archive values in OnlineTrendControl: https://support.industry.siemens.com/cs/attachments/109801003/WinCC_V74_SP1_Update18_Readme.pdf
Siemens, WinCC: Working with WinCC, System Manual, 11/2019, A5E47940912-AA, Tag Logging and creating controls from archive tags: https://support.industry.siemens.com/cs/attachments/109773058/WinCC_Working_with_WinCC_en-US_en-US.pdf

Troubleshoot Missing Analog Trend History in CEMAT CS