Designing SCADA Alarm Callouts That Actually Wake Someone Up
Remote notification is a delivery channel, not an alarm system. Picking which alarms page out, escalation timers that match humans, and proving delivery.
Articles
Practical SCADA notes
Field-oriented references for HMI/SCADA systems, industrial communication, alarms, tags, historians, and project delivery.
Your Valve Reports Closed but the Flow Says Otherwise: Limit Switch and Travel Timer Logic
Turning two limit switches and a travel timer into honest valve state: transit handling, discrepancy alarms, and catching a slowing actuator early.
Rate-of-Change Alarms: Catch a Runaway Before the High-High Ever Trips
Designing rate-of-rise and rate-of-fall alarms: window length, noise filtering, units, and the quality gating that stops them screaming on comms recovery.
Alarm Help Text That Survives 02:00: Cause, Consequence, and the Action You Actually Want
Alarm help text is written once during rationalization and never read again. What belongs in cause, consequence and response for a 02:00 operator.
Newest-First Alarm Summaries Hide the Critical Alarm During a Flood
During a flood a newest-first summary pushes the critical alarm off screen, and a filter left on erases it. Picking a default sort that holds.
HMI Color and Shape Semantics for Operator Screens
Practical HMI notes for using color, shape, text, and state rules so operator screens stay readable during abnormal conditions.
Poll These Switch Points Before You Blame the PLC
Intermittent bad quality usually starts at a switch port. Which SNMP objects are worth polling, why counters only mean anything as rates, and trap gaps.
The Bypass Nobody Cleared: Making Maintenance Overrides Visible in SCADA
A maintenance bypass is an operating state, not a comment field. Tag naming, ISA-18.2 out-of-service handling, expiry rules, and the audit trail.
Alarm Horn Silence Is Not Acknowledgement — Split the Buttons
Wiring horn silence to the acknowledge tag corrupts the event log from day one. Splitting silence, acknowledge, reset and shelve under ISA-18.2.
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.
Why Every Alarm Ends Up High Priority, and How to Rank Them by Response Time Instead
Building an alarm priority matrix that ranks by consequence and operator response time, with the EEMUA 191 targets that keep high priority rare.
Acknowledged Isn't Cleared: How to Run a Standing Alarm Review
Standing alarms are acknowledged but still active. Reviewing them against the ISA-18.2 stale-alarm metric before they become summary wallpaper.
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.
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.
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.
Bad Quality Isn't Zero: Handling SCADA Tag Quality Without Lying to the Operator
OPC DA quality words, OPC UA StatusCodes, DNP3 flags — and how to display, alarm and historize them so a dead signal never reads as a valid value.
Why Alarm Acknowledge, Latch, and Reset Must Stay Separate Signals
One shared bit for acknowledge and reset is how alarms vanish while the fault is live. Separating active, latch, ack, return-to-normal and reset.
The Banner Was Empty and the Plant Was Not Quiet
Filtering an alarm banner is not suppressing an alarm, and ISA-18.2 draws that line for a reason. What the default view owes the operator during a flood.
Why Two SCADA Screens Disagree About the Same Pump
One screen says the pump is stopped, the report says faulted. The fix is a derived status tag with a written priority order that every client shares.
How Long Should an Alarm Delay Be? Set It From Process Time, Not a Default
Setting on-delays, off-delays, debounce and deadband from process behaviour and ISA-18.2 — filtering nuisance alarms without hiding the first warning.
Finding the First-Out Alarm When Your SCADA Floods
Alarm floods bury the initiating cause. Preserving first-out, trusting sequence-of-events timestamps, and stopping comms failures becoming floods.
HMI Permissive and Interlock Display Checklist
How to show permissives, interlocks, inhibits, bypasses, command readiness, and first-out causes on practical HMI screens.
Alarm Rationalization Workshop Checklist
Running alarm rationalization sessions that produce usable priorities, causes and operator response guidance instead of another unread spreadsheet.
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.
The One Bit That Decides Whether a SECS/GEM Alarm Is Set or Cleared
S5F1 carries ALCD, ALID and ALTX. Bit 8 of ALCD is set-versus-clear, and dropping it leaves an MES alarm list that never goes green. Plus the S5F5/S5F6 recovery after a host restart.
From SCADA Signals to Operational State
How raw SCADA, HMI and protocol values become useful machine state, process state, alarm state and control state, and where each one is decided.
HMI Faceplate Design Checklist
A practical checklist for designing HMI faceplates that operators can use quickly, consistently, and safely during normal operation and troubleshooting.
Shelving vs. Suppression: Quieting SCADA Alarms Without Hiding Real Risk
How ISA-18.2 splits shelving, designed suppression, out-of-service and interlock bypass — and configuring them so every hidden alarm keeps an owner.
Try a Live Operational State Tutorial
A short hands-on walkthrough that turns one temperature signal into alarm state, switch action, HMI feedback, and an event log using the StateX tutorial.
Common SCADA Alarm Design Mistakes
Practical alarm design mistakes that create nuisance alarms, floods, operator confusion, and poor incident response.