Standard Cubic Meters, Actual Cubic Meters, and the Gas Total Nobody Agrees On
Pressure and temperature compensation for gas flow: which meters need it, the absolute-pressure trap, where the math belongs, and a failed P transmitter.
Articles
Practical SCADA notes
Field-oriented references for HMI/SCADA systems, industrial communication, alarms, tags, historians, and project delivery.
Turning Tank Level Into Volume Without Getting the Inventory Wrong
Building a strapping table into SCADA: segment geometry, interpolation spacing, where the calculation runs, and the density trap in hydrostatic level.
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.
Where to Do the Square Root on Orifice Flow, and Why It Jitters at Low Flow
Orifice DP goes as the square of flow, so someone takes the root — transmitter, PLC or SCADA. Do it twice, or skip the low-flow cutoff, and it lies.
Building a SCADA Totalizer That Survives Counter Rollover and Meter Resets
Computing usage across a wrapping counter without inventing phantom flow: register width, correcting the delta once, and rollover versus meter reset.
Report-by-Exception in SCADA: Why It Breaks When You Treat It Like Slow Polling
Running report-by-exception and change-of-state — DNP3 events, deadbands, heartbeats, integrity polls — without losing short events or stale values.
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.
Why Your MQTT Dashboard Jumps Backward: Timestamps, Sequence Numbers and Replay
MQTT arrival order is not process order. Why the DUP flag never catches the duplicates that hurt, Sparkplug's 8-bit seq wrap, and the MQTT 5.0 properties that fix stale retained state.
Use MQTT Shared Subscriptions to Scale Consumers — but Keep the Historian Out of the Pool
Shared subscriptions split an MQTT stream across workers — and will quietly halve your historian feed and scramble trend order if you point them wrong.
How to Size an MQTT Wildcard Subscription Before It Floods Your Historian
Estimating the real load behind site/#, and the MQTT 5.0 features that actually contain it: Retain Handling, shared subscriptions, Receive Maximum, SUBACK reason codes.
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.
Which OPC UA Name Should Your SCADA Store: NodeId, BrowseName, or DisplayName?
NodeIds regenerate, browse paths move, DisplayName is a label. Picking the reference your HMI and historian store so firmware doesn't blank a screen.
How to Set OPC UA Deadbands Without Hiding a Drifting Transmitter
Choosing DataChangeFilter settings — absolute versus percent deadband, DataChangeTrigger, queue size — so a filter cuts noise, not real movement.
Backfilling a Historian Gap with OPC UA HistoryRead Without Double-Counting
Repairing a historian gap with OPC UA HistoryRead: scoping the window, letting returnBounds handle edges, keeping Bad quality, and paging safely.
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.
MQTT Payload Schema Versioning for SCADA Edge
Versioning MQTT telemetry payloads so historians, HMI clients, MES connectors and analytics survive a field change instead of breaking on one.
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.
How to Fix Bad Historian Data Without Overwriting the Original
A failed transmitter pegs a tag at full scale for eleven hours. Correcting the record with an audit trail that survives review, raw sample intact.
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.
Why the PLC and MES Shift Counts Never Match, and Which One to Trust
The shift report says 1,738 good parts and the HMI says 1,742. Where to look first: counter style, historian deltas, S6F11 event time, or the spool.
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 Keep MQTT Store-and-Forward From Punching Holes in Your Historian
Why an MQTT edge gateway loses data during a WAN outage, and how to buffer with source timestamps, sequence numbers and a replay policy that holds.
Your Historian Event Frame Is Only as Good as Its End Trigger
Event frames pay off only if their boundaries hold. Where to take start and end triggers, what to capture as attributes, and frames that never close.
Every S6F11 Arrived and the Lot History Still Has Holes
Where lot traceability breaks when built from equipment events: missing lot context, GEM event time, spool replay order, and split/merge genealogy.
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.
How to Commission Analog Scaling Without Trusting the HMI Number
A field walkthrough for analog scaling: ranges, engineering units, Modbus word order, NAMUR thresholds — so PLC, SCADA, HMI and historian agree.
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.
OPC UA Sampling vs Publishing: Why Connected Doesn't Mean Good Data
How sampling interval, publishing interval, queue size, deadband and the KeepAlive/Lifetime pair decide whether your client and historian see the process.
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.
OPC UA Certificate Renewal Checklist
A practical checklist for renewing OPC UA application certificates without breaking SCADA clients, historians, gateways, or production HMI connections.
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.
Designing Sparkplug B Topics You Won't Have to Rename Later
Laying out Sparkplug B group, edge node and device IDs — plus birth certificates, aliases and STATE — so a rename doesn't break every subscription.
Historian Basics
What an industrial historian does, what to plan before collecting data, and common mistakes in historian projects.
OPC UA Client Commissioning Checklist
A practical checklist for commissioning OPC UA client connections from SCADA, HMI, historian, or gateway software to PLCs and automation servers.
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.
What is a SCADA Tag?
A practical definition of SCADA tags and how they connect PLC addresses, alarms, trends, screens, and reports.
HMI vs SCADA vs MES vs Historian
A field-oriented comparison of common industrial software layers and where their responsibilities overlap.
What is SCADA?
A practical explanation of SCADA systems: what they do, where they fit, and what to watch for on real projects.