Your Loop Isn't Badly Tuned — The Valve Is Sticking: Finding Stiction in Trend Data
A level loop still cycling after two retunes is usually the valve. Reading stiction off PV/OP trends, proving it with a step test, and monitoring it.
Articles
Practical SCADA notes
Field-oriented references for HMI/SCADA systems, industrial communication, alarms, tags, historians, and project delivery.
Why Your HMI Trend Draws a Flat Line Through a Ten-Minute Outage
Held values, dropped quality codes and late samples inserted at arrival time each make a trend lie after an outage. Working out which one you have.
A Straight Line in Your Historian Isn't Always Data
How historians hide communication gaps behind interpolated lines and held values, and the quality rules that keep bad data out of a shift report.
How to Scale HMI Trend Pens So the Screen Doesn't Lie to the Operator
Take trend axis defaults from OPC UA EURange, not 0-100. Clamping at 100% hides NAMUR NE 43 fault currents that land at -2.5% and 106.25%, plus alarm lines and commissioning checks.
Historian Trend Annotations: Store Operator Events as Events, Not Fake Tags
Recording calibration, manual mode and bypass windows as event records separate from the sampled stream, joined back by asset ID and time window.
Why Your Historian Missed the Pump Trip: Exception vs Periodic Collection
Exception and periodic collection store different truths. Picking per tag so a 300 ms interlock survives, and proving the choice during commissioning.
Renaming Historian Tags Without Losing Three Years of Trend
Historians key archive data to a point ID or a name string, so a rename can split a tag's history in two. What to verify before operators find the gap.
A Trend Cursor Only Proves What the Clocks Agree On
HMI, historian, PLC log and alarm list stamp one event seconds apart. Where each timestamp is born, and which one to trust during an incident.
How to Downsample Historian Data Without Losing the Trip That Mattered
Averaging old process data hides trips and flattens peaks. Classifying tags, picking a method per class, and testing a purge job before production.
How to Validate a Historian Calculated Tag Before Reports Depend On It
A calculated tag quietly becomes an official number. Checking formula, quality rules, period boundaries and counter resets before reports depend on it.
Why Your Historian Shows the Pressure Dropping After the Trip
How historian timestamps go wrong — clock drift, NTP versus PTP, OPC UA source time, late data, DST — and catching it before a report dispute does.
How to Set a Historian Backfill Policy Before Late Data Rewrites Your Reports
Store-and-forward hands you hours-old samples when a link recovers. Which timestamp wins, what a late value may overwrite, and how to mark it.
Setting Historian Deadbands So Trends Aren't Noise or Lies
Picking historian deadbands and compression from the instrument and the process, not HMI decimal places, so trends keep movement without storing noise.
Historian Basics
What an industrial historian does, what to plan before collecting data, and common mistakes in historian projects.
Designing SCADA Trend Displays Operators Can Troubleshoot From
Trend screens that answer the operator's real question during an upset: grouping by loop, choosing scales, and drawing a comms gap as a gap.