HSMS Select Timeout: Three Causes That Look Identical in the Host Log
Silence, mismatched SystemBytes, or a wrong SessionID: real captures of three Select failures and the SEMI E37 timers T5, T6 and T7 behind each log line.
Articles
Practical SCADA notes
Field-oriented references for HMI/SCADA systems, industrial communication, alarms, tags, historians, and project delivery.
PRP and HSR Give You Zero-Gap Redundancy — and Hide a Dead LAN
How IEC 62439-3 PRP and HSR deliver bumpless redundancy for SCADA and IEC 61850, why a failed LAN goes unnoticed, and what to monitor at commissioning.
Making Online PLC Edits Without Tripping the Running Process
Changing ladder logic in a running PLC safely: online edit versus download, scan-order traps, seal-in glitches, forces, and a pre-edit checklist.
Getting Modbus RTU Through a Serial Device Server Without Dropping Frames
Commissioning a serial-to-Ethernet device server carrying Modbus RTU: operating mode, packing timers, TCP framing, idle timeouts and half-duplex control.
Why Your Modbus Gateway Pings Fine but SCADA Still Goes Stale
A Modbus TCP-to-RTU gateway can answer ping and still drop requests. Finding the queue saturation behind stale tags, and tuning the driver for it.
Your HMI Breadcrumb Should Follow the Plant, Not the Project Tree
Make each HMI screen state where it is: ISA-101.01 display hierarchy as the breadcrumb, command labels that show scope, and tests for copied screens.
Your HMI Says Step 40 — It Should Say What Step 40 Is Waiting For
A sequence screen showing only a step number sends the operator hunting across four displays. Separate state, step, and hold reason, and latch the reason.
How to Keep a Reusable HMI Faceplate From Commanding the Wrong Pump
Popup context passing for reusable faceplates: one stable equipment key, command binding that fails closed, and telling a broken binding from bad quality.
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.
How Many Modbus TCP Clients Can One PLC Actually Take?
Modbus TCP devices cap simultaneous connections lower than you think. Inventorying clients, reading real socket behaviour, and protecting the HMI.
The Modbus TCP Bug Where the Socket Is Fine but the Values Are Wrong
How a mishandled transaction ID lets a Modbus TCP gateway hand your SCADA driver the wrong register's value — and how to prove it with a capture.
Good Quality, Stale Value: Reading OPC UA StatusCode and Timestamps
Using StatusCode severity bits, SourceTimestamp and ServerTimestamp to catch frozen data, cached gateway values and clock drift a value-only HMI hides.
Stop Scanning Every SCADA Tag at One Second
Why a flat 1-second scan overloads PLCs and gateways, and how scan classes and load shedding keep the data operators act on fast under stress.
Why Adding a Rework Loop Made Our First-Pass Yield Go Up
Rework quietly breaks linear MES route models. How to bind visit numbers, dispositions, and equipment events to the right route step instance.
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.
An Equipment Constant Is a Recipe Change With a Different Name
The host wrote the EC, EAC came back 0, and nine lots ran on the old value. SEMI E5 EAC codes, a real S2F13 readback, S2F29, and the SAT matrix.
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.
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.
Modbus RTU Timeouts Are Usually a Wiring Problem: An RS-485 Commissioning Walkthrough
Commissioning a Modbus RTU link the right way: prove polarity, termination, biasing and grounding before you ever open the register map.
OPC UA Alarms & Conditions: Getting Retain, Acknowledge, and Reconnect Right in SCADA
Commissioning OPC UA Alarm & Condition subscriptions: event filters, the Retain flag, ConditionRefresh, and the failures that appear on reconnect.
How to Test SCADA Server Switchover Without Fooling Yourself
A green redundancy icon proves the heartbeat works and nothing else. What to check on clients, alarms, historian and background jobs during a failover.
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.
The HMI Accepted the Setpoint. The PLC Didn't.
Why setpoint entry fails on the acknowledgment path, splitting display limits from PLC hard limits, and the tests that catch silent rounding.
Rotating an MQTT Broker Certificate Without Dropping Your SCADA Clients
A staged plan for rotating MQTT broker, client and CA certificates without breaking publishers, store-and-forward queues or Sparkplug birth sequences.
In OPC UA, a Trusted Certificate Is Not Permission to Write
How OPC UA separates certificate trust, user identity and Part 18 role mapping — and commissioning writes so the wrong session can't move a setpoint.
A Manual Override You Can't Audit Is a Fault You Can't Find
A forced valve and a substituted flow reading are different overrides, and one Manual bit can't tell them apart. Logging that survives a server restart.
Why Your Modbus TCP Gateway Reads the Wrong Slave
The Modbus unit identifier is 'useless' on TCP until a gateway is involved. How routing works behind serial gateways, and finding the slave that answered.
OPC UA Reverse Connect: When the Server Has to Dial the Client
How reverse connect flips the TCP direction through a cell firewall, and the certificate, endpoint and diagnostic traps that still bite afterward.
Your SCADA Backup Isn't a Backup Until It Restores on a Clean Machine
A SCADA restore drill on a clean machine: what the backup set misses, OPC UA certificate traps, RPO and retention per artefact, and a measured RTO.
SCADA Service Account Password Rotation: Trigger It on Events, Not a Calendar
Nobody memorizes a service account password, so a 90-day policy buys little. What IEC 62443-3-3 SR 1.2 and NIST 800-63B actually ask for.
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 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 Connects Fine but Every Tag Reads Bad: the NodeId Moved
After a PLC download the session opens and every item returns Bad_NodeIdUnknown. How namespace indexes and client caches shift, and what to check first.
Alarm Rationalization Workshop Checklist
Running alarm rationalization sessions that produce usable priorities, causes and operator response guidance instead of another unread spreadsheet.
Why Operators Code Everything as "Other" — Fixing an MES Downtime List
Designing downtime reason codes operators pick correctly under pressure: prompt timing, auto-coding from PackML state, and the fields reports need.
Telling a Dead MQTT Gateway from a Quiet One on the HMI
Using Last Will, birth messages and retained state so a SCADA screen shows offline, stale and healthy as three things — not one green icon that lies.
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.
Why Your HMI Should Never Merge Mode and State Into One Field
Mode is who may command the equipment; state is what it is doing. SEMI E30's control state model splits them — here is how to split the HMI to match.
Five HMI/SCADA Project Decisions That Are Expensive to Undo
Tag names, alarm counts, screen hierarchy, broken-wire handling, and command state after a restart — with the numbers ISA-18.2, ISA-101.01 and NAMUR NE 43 already give you.
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.
HMI Faceplate Design Checklist
A practical checklist for designing HMI faceplates that operators can use quickly, consistently, and safely during normal operation and troubleshooting.
Why Remote I/O Drops Four Minutes After a Clean Switch Startup
Industrial Ethernet switch commissioning by the numbers: the IGMP querier and the 260-second membership interval, auto-negotiation half-duplex traps, RSTP's 20-second max age against IEC 62439-2 ring classes, and the real port numbers to test.
SCADA Commissioning Checklist
A commissioning checklist for validating HMI and SCADA screens, tags, alarms, trends, historians, users, backups and comms paths before handover.
SCADA Tag Naming Guide
A practical guide for creating readable, maintainable SCADA tag names across equipment, signals, alarms, trends, and reports.