Trend Looks Perfect During an Outage? Check the Quality Gaps
A continuous trend line can conceal missing or bad-quality data. Review raw quality and interpolation behavior before concluding that the process stayed stable.
Original data-quality example; inspect the actual query and visualization settings.
What is happening?
History queries may aggregate, interpolate, or omit invalid records. A visual line between valid points is a rendering choice, not proof of measurements throughout the interval. Reports should make coverage and quality visible.
Check these five things
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Query raw values with quality and timestamps.
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Locate communications or sensor-quality events.
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Check interpolation and bad-quality handling in the trend.
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Compare sample coverage with the reporting interval.
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Label gaps or uncertain periods appropriately.
Worked example
A teaching dataset has valid values at 12:00 and 12:10 but no valid observations between them. Drawing a straight line suggests a smooth transition, yet the missing interval could contain unobserved changes. The report should not treat that line as measured evidence.
Quick diagnostic reference
| Display feature | What to verify |
|---|---|
| Continuous line | Interpolation rules |
| Average | Included sample quality |
| Empty interval | Coverage reporting |
The mistake to avoid
Do not replace missing measurements with zeros unless zero is the defined meaning. That changes the dataset and can distort averages or totals.
How to verify the fix
Use a reference dataset with valid, bad, and missing intervals. Confirm charts and calculations preserve the intended distinctions.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Inductive Automation: Quality codes and overlays. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.