Category: Control Systems
Your PLC Trend Shows a Slow Oscillation? It Could Be Aliasing
A trend can display a frequency that does not exist in the process.
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Flow Reads Too High at Low Load? Check for Double Square-Root Extraction
A differential-pressure flow measurement may already be linearized before reaching the PLC.
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Flow Total Is Exactly 60 Times Wrong? Follow the Time Units
A totalizer can be numerically consistent yet use incompatible time units.
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The Sensor Is Fast but the PLC Reacts Late? Add Up Every Filter
Several modest filters can combine into a significant response delay.
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HMI Displays Fahrenheit but Writes Celsius? Test Both Directions
A converted display can look correct while an operator entry writes the wrong units.
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Alarm Appears on SCADA but Nobody Gets Notified? Trace the Pipeline
An active alarm and a delivered notification are separate outcomes.
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Database Is Back but History Is Still Missing? Inspect Store-and-Forward
Restoring a database connection does not guarantee that queued history has been written successfully.
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Production Report Repeats an Hour? Check Daylight-Saving Time
Local clock labels can repeat during a daylight-saving transition.
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Two Trends Look Identical but Values Differ? Check the Axes
Chart shape alone does not establish equal values or a causal relationship.
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OEE Jumps After a Dashboard Update? Audit the Denominator
An OEE improvement can come from a changed calculation rather than changed production.
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