Category: Control Systems
PID Output Stuck at 100%? The Integral May Be Hiding the Real Problem
A PID output at its limit does not prove the tuning is weak.
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Trend Looks Perfect During an Outage? Check the Quality Gaps
A continuous trend line can conceal missing or bad-quality data.
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Temperature Runs Away After Enabling PID? Check the Control Direction
A loop that drives farther from setpoint may have the wrong control direction.
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Alarm Disappeared from the Screen? Check Shelving and Filters
An alarm absent from one display may still be active.
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PID Looks Badly Tuned? Check Whether SP and PV Use the Same Scale
A PID cannot interpret a setpoint in degrees correctly when its process input represents percent.
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Operator Enters 12.34, but the PLC Gets 12.3? Trace Precision End to End
Displayed decimal places, accepted entry precision, and stored precision can differ.
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PID Output Spikes When the Setpoint Changes? Check Derivative Kick
A sharp output spike exactly when setpoint changes can come from derivative acting on error.
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Production Count Doubles After a Retry? Give Each Event a Durable Identity
Retrying a database write can duplicate a production event when the first write succeeded but its acknowledgment was lost.
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A Tiny Sensor Ripple Is Shaking the Valve? Check the Derivative Term
A small measurement ripple can create a large derivative contribution.
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SCADA Log Stops Overnight? Check Disk Space and Rotation Limits
A logging process can keep running while new records stop reaching disk.
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