Industrial automation runs on jargon. A single conversation about a tank battery can involve HIHI setpoints, deadbands, Modbus registers, and a historian — and if you are new to SCADA, or coming from the IT side, half of those words are guesses. This glossary defines 78 terms the way a field engineer would explain them across the hood of a truck: plainly, with oil & gas examples where they help. Bookmark it, link to it, and jump straight to any term with the A–Z index below.
A network design in which the control system has no connection to the internet or the corporate network — physically or logically isolated. It is the most conservative OT security posture, common in pipelines and critical infrastructure. Air-gapped sites cannot use cloud SCADA at all, which is why Merobix also offers an on-premise deployment that runs entirely on your own servers with full data residency.
An automatic notification that a measured value crossed a configured limit and a human needs to act — tank level too high, pump amps too low, communication lost. A good alarm is timely, specific, and actionable; a bad one trains operators to ignore the system. Modern platforms deliver alarms by SMS and email; Merobix commits to delivery in under 30 seconds. See our guide to oilfield alarm monitoring.
A burst of more alarms than an operator can meaningfully process — commonly benchmarked as more than ten alarms in ten minutes. Floods usually happen during a process upset, exactly when clarity matters most: one root cause (a compressor trip) cascades into dozens of downstream consequence alarms, burying the alarm that actually explains the event.
The systematic review of every configured alarm against a documented philosophy: does it require operator action, what is its priority, what are the right limits and deadbands? Rationalization is the core discipline of ISA-18.2 and the cure for nuisance alarms. Our alarm management comparison looks at how the major platforms support it.
A controlled, operator-initiated pause on a specific alarm — typically for a nuisance alarm that keeps re-annunciating while maintenance is pending. The key difference from simply disabling it: a shelved alarm has a time limit and automatically un-shelves itself, so nothing gets forgotten in a disabled state for three years.
Logic-driven hiding of alarms that are expected consequences of a known condition. Classic example: when a well is shut in for workover, its low-flow and low-pressure alarms are suppressed automatically so they do not pollute the alarm list. Unlike shelving, suppression is designed into the system rather than invoked by an operator.
Originally a hardware panel of backlit windows in the control room, each engraved with an alarm legend, that lit up and sounded a horn when its condition tripped. The word survives as a verb — an alarm "annunciates" when it presents itself to the operator — and the hardware survives as the alarm summary screen in every modern HMI.
The standard protocol of building automation: HVAC, chillers, air handlers, and facility power systems. It matters to SCADA buyers because monitoring increasingly crosses the line between process and facility — a data center or plant utility building speaks BACnet, and Merobix includes a BACnet driver among its 20 protocol drivers.
A hazardous-location classification under the National Electrical Code: an area where flammable gases or vapors are not normally present but could be under abnormal conditions — most wellsites and tank batteries qualify. Electrical equipment installed there, including control panels, must be built and rated for it. Merobix fabricates UL 508A panels rated for C1D2 service.
A SCADA platform hosted and maintained by the vendor and accessed through a web browser, instead of software you install on servers you own. The vendor handles patching, backups, and redundancy; you handle logging in. Merobix cloud deployments are managed end to end and typically live in 3–5 days. The full trade-off is covered in our cloud vs on-premise comparison.
Measurement taken at the point where ownership of oil or gas changes hands — lease to purchaser, producer to pipeline. Because money rides directly on the number, custody-transfer measurement is held to contractual accuracy standards, witnessed proving, and audit trails that ordinary process measurement never faces. See LACT unit and EFM.
A control system built for continuous, closed-loop process control inside one large facility — a refinery, a chemical plant — where thousands of PID loops run in redundant controllers. SCADA, by contrast, grew up supervising equipment scattered across large distances. The line has blurred, but the instincts differ; our SCADA vs DCS comparison walks through when each fits.
A margin a value must travel back through before an alarm clears or a change is recorded. A tank alarm set at 80% with a 2% deadband will not clear until the level drops below 78% — so a level sloshing around exactly 80% does not generate a hundred alarm/clear pairs an hour. Deadbands are the cheapest alarm-management fix that exists.
A live virtual model of a physical asset, continuously updated with its real operating data, used to visualize, analyze, or simulate the asset. The term covers everything from a full physics simulation of a compressor to — more honestly, in most operations — a well-organized set of tags, trends, and dashboards that faithfully mirror what the equipment is doing right now.
Distributed Network Protocol 3, the telemetry workhorse of North American water and electric utilities. Its distinguishing strengths are event buffering with timestamps — an outstation remembers what happened while communications were down and reports it accurately later — and efficient report-by-exception operation over slow links. Merobix includes a DNP3 driver.
Recording when equipment stopped, for how long, and why — automatically from run-status tags, with reason codes filled in by operators. It is the raw material of OEE, deferred-production accounting, and every argument about which pump deserves replacement. If you want to know what downtime costs you, run the numbers in the Merobix ROI calculator.
A small industrial computer installed near the equipment that collects data locally, optionally processes or buffers it, and forwards it to the central platform. "Edge" simply means close to the machine instead of in a data center. Edge devices are what let modern architectures poll fast locally while sending only meaningful changes over a cellular link — more in our IIoT vs SCADA explainer.
The flow computers and audited records used to measure natural gas volumes for accounting and custody transfer. EFM data is different from ordinary SCADA polling: it carries the configuration, events, and hourly/daily history that gas accounting and auditors require, following industry measurement standards. Pulling EFM alongside real-time data is a standard requirement in gas gathering.
A multi-stage centrifugal pump hung downhole and driven by an electric motor — the muscle behind many high-volume oil wells. ESPs are expensive and die expensively, which makes them prime monitoring candidates: rising motor temperature, falling intake pressure, and drifting amps usually show up in trends days before the failure that kills the run.
An industrial protocol that runs the Common Industrial Protocol (CIP) over standard Ethernet, managed by ODVA. It is the native language of Allen-Bradley PLCs, which makes it unavoidable in North American plants. Merobix includes an EtherNet/IP driver and also programs the Allen-Bradley controllers on the other end of the wire.
The automatic switch from a failed primary server to its standby. Good failover is measured in seconds, requires no operator action, and preserves alarm states and history. Bad failover is a phone call at 2 a.m. and a blank screen. The mechanics — heartbeats, split-brain arbitration, client redirection — are covered in our high availability guide.
Factory Acceptance Test and Site Acceptance Test. The FAT proves a panel or system works as specified before it leaves the builder's shop — power it up, force the I/O, trip the alarms, sign the punch list. The SAT repeats the proof after installation, with real field wiring and real process conditions. Skipping either is how surprises reach commissioning day.
One of the IEC 61131-3 PLC programming languages: logic drawn as blocks — timers, comparators, PID controllers — wired together on screen. Function block diagrams shine for continuous control and math-heavy logic, while ladder logic remains the favorite for discrete interlocks that electricians need to troubleshoot at 3 a.m.
The hardware or software layer that translates between field-device protocols and the SCADA platform — speaking Modbus to a flow computer on one side, publishing to the cloud on the other. A well-designed gateway also buffers data locally during communication outages (store-and-forward), which matters enormously on cellular-connected sites.
Regulatory greenhouse-gas emissions reporting — for US oil and gas operators, primarily the EPA's annual reporting program. What used to be a spreadsheet scramble is increasingly fed directly from SCADA: flare meters, tank-vent estimates, and equipment runtime all live in the historian already. Our SCADA reporting guide covers turning that data into filings.
A protocol that superimposes digital data on a standard 4-20 mA instrument signal, so a transmitter can report its measurement the analog way while also carrying range, diagnostics, and secondary variables digitally. HART-IP brings the same data over Ethernet networks — and is one of the 20 protocol drivers Merobix ships.
The discipline of designing the monitoring system so that hardware failures, software crashes, network outages, and maintenance never create a gap an operator would notice. In practice it means redundancy plus automatic failover plus tested recovery — and it is usually expressed as an uptime percentage backed by an SLA.
The four standard alarm limits on an analog value. HI and LO are warnings — the value has left normal range, look at it. HIHI and LOLO are critical — act now, before the tank overflows or the pump runs dry. Separating warning from critical is what lets operators triage: a HI at 2 a.m. can wait for coffee; a HIHI cannot.
The time-series database that records every tag value over time — the system's memory. The historian answers the questions that matter after the fact: what was the pressure doing before the trip, how long was the compressor down last month, what did we produce in March. Architecture and sizing are covered in our SCADA server guide.
Querying several historians — one per site, plant, or region — as if they were a single database, without physically moving the data. Federation is how a multi-site operator trends a Permian well against an Eagle Ford well on one screen. Merobix supports historian federation on the Enterprise plan.
The screens people actually look at: process graphics with live values, alarm lists, trend displays, and control buttons. "HMI" can mean a small touchscreen on one machine or the full operator interface of a SCADA system. The craft is in restraint — a good HMI makes the abnormal obvious instead of decorating the normal. See what the Merobix interface looks like in practice.
A second, fully synchronized SCADA server running in parallel with the primary, exchanging heartbeats, ready to take over automatically within seconds. Contrast with cold standby — a backup that must be manually restored, losing hours. Hot standby redundancy is included in the Merobix Enterprise on-premise plan; the full architecture is in our redundancy guide.
A telecontrol protocol that carries supervisory data over TCP/IP networks, widely used by electric utilities in Europe and much of the world outside North America (where DNP3 dominates instead). If your equipment or your market touches international power infrastructure, you will meet it — Merobix includes an IEC 60870-5-104 driver.
The international family of standards for industrial control system cybersecurity — the OT counterpart to IT's ISO 27001. It defines security levels, roles for asset owners and vendors, and the zones-and-conduits segmentation model. Practical application is walked through in our secure OT network guide.
The standard that defines the alarm management lifecycle: write an alarm philosophy, rationalize every alarm against it, monitor alarm-system performance (rates, floods, chattering), and audit the results. If your operators receive hundreds of alarms per day, ISA-18.2 is the roadmap out — and its metrics are the vocabulary auditors and consultants will use.
Lease Automatic Custody Transfer unit — the metering skid that measures crude oil quality and volume as it leaves the lease and ownership changes hands. A LACT samples for BS&W (basic sediment and water), proves its meter, and records everything, because its totalizer is effectively a cash register. LACT monitoring is standard fare on a tank battery SCADA screen.
The most widely used PLC programming language, drawn to look like the relay ladder diagrams it replaced: power rails on the sides, rungs of contacts and coils across. Electricians can read it, which is precisely why it has outlived prettier languages for decades. We explain it from scratch in What Is Ladder Logic.
A regulatory program requiring operators to find and fix fugitive emissions leaks — valves, connectors, seals — on a documented schedule, using optical gas imaging or analyzers. LDAR is inspection-driven rather than SCADA-driven, but continuous monitoring data increasingly supports it by flagging pressure anomalies and vent events between surveys.
Requiring a second proof of identity beyond a password — a code, an app prompt, or a hardware key — before granting access. For remote-accessible SCADA, MFA is no longer optional; it is the control that turns a phished password into a non-event. Merobix Enterprise supports FIDO2 hardware keys alongside LDAP, SAML, and RADIUS integration — details on the security page.
The formal process of reviewing, approving, and documenting any modification to equipment, process conditions, or control logic before it happens. In PSM-covered facilities MOC is a legal requirement, but the logic applies everywhere: the alarm setpoint someone "temporarily" changed in 2019 is still temporary because no MOC record exists to say otherwise.
The serial version of the oldest protocol still in daily service — Modbus over RS-485 or RS-232 wire, one master polling numbered registers on daisy-chained slaves. It is slow, simple, and utterly everywhere in the oilfield: flow computers, VFDs, tank gauges. Simplicity is the feature; when it breaks, a multimeter and patience will fix it.
Modbus carried over ordinary Ethernet networks — same registers, same simplicity, modern transport. It is the closest thing industrial automation has to a universal language: if a device speaks anything, it speaks Modbus TCP. How registers, function codes, and polling actually work is explained in our plain-English Modbus guide.
A lightweight publish-subscribe messaging protocol: devices publish data to a central broker, and anything that cares subscribes. Born for unreliable, low-bandwidth links, it is ideal for cellular-connected oilfield sites — devices report on change instead of being polled. How it compares to OPC UA is covered in MQTT vs OPC UA.
A rating system for electrical enclosures describing what they keep out. NEMA 4 means hose-directed water and windblown dust; NEMA 4X adds corrosion resistance — the standard call for coastal and chemical service; NEMA 7 is for explosive atmospheres. Specifying the wrong NEMA rating is how a $400 enclosure ruins a $40,000 panel in one Gulf Coast summer.
A single score — availability × performance × quality — expressing how much of a machine's theoretical maximum output was actually produced. An 85% OEE is considered world-class in manufacturing. Its honesty depends entirely on honest downtime tracking underneath; more in our manufacturing monitoring guide.
A deployment that runs entirely on servers or virtual machines you own and control — behind your firewall, compatible with an air gap, with every byte of data resident on your hardware. It trades the convenience of cloud hosting for control and isolation. Merobix offers the same platform both ways: managed cloud or on-premise on your infrastructure.
OPC Data Access, the original industrial data-sharing interface, built on Windows COM/DCOM in the 1990s. It connected everything for two decades and still runs in older plants — along with the DCOM configuration headaches it is famous for. New designs use OPC UA; existing OPC DA servers are typically bridged rather than replaced. Merobix supports both.
OPC Unified Architecture — the modern successor to OPC DA: platform-independent, firewall-friendly, encrypted and authenticated by design, with rich information models instead of flat tag lists. It has become the default northbound interface on new PLCs and instruments, and one of the two protocols (with MQTT) at the center of every modern architecture debate.
Operational technology — the systems that watch and control physical equipment — versus information technology, the systems that run the business. The two worlds prize different things (OT: availability and safety; IT: confidentiality and patching), and "OT/IT convergence" is the ongoing project of connecting them without importing each other's failure modes.
The proportional-integral-derivative algorithm — the workhorse of continuous control. It continuously compares a measurement to its setpoint and adjusts an output (a valve, a motor speed) to close the gap: proportional to the current error, integral to accumulated error, derivative to the rate of change. Tuning the three gains is equal parts math and folklore.
The ruggedized industrial computer that actually runs control logic at the equipment: reading inputs, executing its program, and driving outputs, over and over, in milliseconds. The PLC keeps running whether or not SCADA is watching — which is exactly the division of labor explained in SCADA vs PLC. Merobix programs both Siemens and Allen-Bradley PLCs.
An artificial-lift method for gas wells that uses a free-traveling plunger and the well's own pressure to lift accumulated liquids to the surface. The controller's open/close timing decides whether the well makes gas or drowns — which makes plunger cycle data, casing/tubing pressures, and arrival times some of the most-watched tags on a gas-well SCADA screen.
Maintenance performed on a schedule or a runtime interval to prevent failures rather than react to them — oil changes at 500 run-hours, valve greasing quarterly. SCADA makes PM honest by supplying actual runtime from run-status tags instead of guesses, and triggering the work order when the meter, not the calendar, says it is due.
The SCADA system cyclically asking each device for its current values — "what's your pressure now? …now? …now?" — at an interval called the poll rate. Faster polling means fresher data and more bandwidth; on a cellular link, polling 500 registers every second is how you discover your data plan's ceiling. The alternative model is report by exception.
The industrial Ethernet standard of the Siemens ecosystem, used for fast, deterministic communication between controllers and I/O. If the plant runs Siemens S7 PLCs, PROFINET is on the network. Merobix ships both PROFINET and Siemens S7 drivers, and programs the Siemens controllers themselves.
The software module that lets a SCADA platform speak a specific device protocol — one driver for Modbus TCP, another for DNP3, another for S7. Driver breadth determines what you can connect without buying middleware: Merobix ships 20 protocol drivers spanning 7 protocol families, from Modbus and OPC UA to Sparkplug B and IEC 60870-5-104.
The OSHA regulatory framework (29 CFR 1910.119) for facilities handling threshold quantities of highly hazardous chemicals. PSM mandates process safety information, operating procedures, training, mechanical integrity, and MOC. SCADA touches it everywhere: alarm records, interlock testing evidence, and historian data all feed PSM compliance.
Granting permissions by job role rather than person by person: operators acknowledge alarms, supervisors change setpoints, administrators edit configuration — and nobody accumulates permissions they should have lost two job changes ago. RBAC is table stakes for a defensible security posture, and audit logs are what make it provable.
Duplicating critical components — servers, historians, network paths, power — so that any single failure leaves the system running. Redundancy is the architecture; failover is the act; high availability is the result. The one rule that matters: redundancy that is never tested should be assumed not to work.
Transmitting a value only when it changes meaningfully, instead of repeating unchanged data on every poll. A tank that sat at 62% all night sends nothing all night. Protocols like DNP3 and Sparkplug B are built around it — and on metered cellular links it is the difference between a $30 and a $300 monthly data bill.
A ruggedized field device that collects I/O at a remote site and reports it over telemetry — historically over radio, today usually cellular. RTUs are built for the middle of nowhere: wide temperature ratings, solar-friendly power budgets, local logging through outages. The RTU/PLC distinction has blurred; the instinct survives: PLCs control, RTUs report.
Software as a Service — and its industrial cousin, SCADA as a Service: the platform delivered as a subscription the vendor hosts, patches, upgrades, and backs with an SLA, instead of a perpetual license you install and maintain. The economics, trade-offs, and gotchas are laid out in our SCADA-as-a-Service guide.
Supervisory Control and Data Acquisition — the system that watches distributed equipment, records what it sees, raises alarms when something is wrong, and lets authorized humans intervene from anywhere. The PLCs and RTUs do the controlling; SCADA does the supervising. If you are starting from zero, begin with our beginner's guide to SCADA.
The target value — the number you want, as opposed to the number you have. A separator level controller with a setpoint of 45% spends its life nudging the dump valve to hold it there. Alarm limits are setpoints too, and changing either kind is exactly the sort of act that deserves an audit trail and, in regulated facilities, an MOC.
A contractual commitment to a measurable service standard — for hosted SCADA, chiefly an uptime percentage, with defined maintenance windows and remedies for misses. An SLA converts "we're pretty reliable" into an enforceable number. Merobix cloud plans carry a 99.9% uptime SLA; plan details are on the plans page.
A specification that turns raw MQTT into a coherent industrial system: a standard topic structure, an efficient binary payload, and birth/death certificates so every subscriber knows which devices are online and what their tags mean. It is the protocol backbone of most unified namespace architectures, and one of the drivers Merobix ships.
Buffering data locally — at the gateway or edge device — while communications are down, then automatically backfilling the historian when the link returns. On cellular-connected sites, store-and-forward is the difference between an outage being a gap in your regulatory record and being invisible. Ask any vendor exactly where their buffering lives and how long it lasts.
A well that injects produced water into a deep disposal formation. SWDs live under regulatory pressure limits and volume reporting requirements, which makes injection pressure, rate, and cumulative volume mandatory SCADA tags — and a HIHI on injection pressure one of the alarms an operator truly cannot afford to miss.
A single named data point in the SCADA system — one pressure, one temperature, one run status, each with a name like WH-101_TBG_PRESS. Tag count is the traditional unit of SCADA sizing and, on many platforms, of pricing; how per-tag licensing shapes cost is dissected in our licensing models guide.
The cluster of tanks and separation equipment at a lease site where produced oil, gas, and water are separated, stored, and measured before sale or disposal. Tank batteries are where monitoring earns its keep in the oilfield: a level transmitter and a HIHI alarm cost almost nothing next to one overflowed tank and the cleanup that follows.
Measuring something in one place and transmitting the reading somewhere else — from the Greek for "remote measurement." It is the founding act of SCADA: the moment a wellsite pressure appears on a screen a hundred miles away, telemetry happened. Radio, satellite, and now cellular and LTE are just the successive vehicles.
A plot of one or more tags over time — and usually the fastest route to understanding what a process actually did. Numbers say the pressure is 180 psi; the trend says it has been climbing since Tuesday. Overlaying tags (casing pressure against plunger arrivals, amps against flow) is where diagnoses happen. Trending is core to the Merobix platform.
The UL standard for industrial control panels. A UL 508A certified shop can build and label panels to it — evidence for inspectors and insurers that the panel's components, wiring, and short-circuit ratings were engineered rather than improvised. Merobix builds UL 508A panels, including C1D2-rated designs; costs and process are in our UL 508A guide.
An architecture in which all business and process data is published into one organized, hierarchical, real-time structure — typically an MQTT broker with a Sparkplug B payload — so any system can subscribe to any data without point-to-point integrations. The concept, and how SCADA fits it, is unpacked in our unified namespace guide.
The percentage of time a system is operational, usually counted in nines. The gaps between nines are bigger than they look: 99% allows 87.6 hours of downtime a year; 99.9% allows 8.8; 99.99% allows under one. For a monitoring platform, every one of those hours is time your alarms may not fire — which is why the number belongs in a contract, not a brochure.
The assembly of valves, spools, and fittings at the surface of a well — the "Christmas tree" — that contains pressure and directs flow. It is the natural first monitoring point: tubing and casing pressure at the wellhead tell you more about a well's health per dollar of instrumentation than anything else on the lease. See our wellhead monitoring guide.
The record that turns a problem into an assigned, trackable task: what is wrong, who fixes it, what parts it took, when it closed. The mature pattern is alarm-to-work-order — a SCADA alarm automatically opening a ticket in the maintenance system. Merobix Enterprise integrates with SAP, Maximo, and ServiceNow for exactly that handoff.
The IEC 62443 model for segmenting an industrial network: group assets with similar security needs into zones (control network, DMZ, corporate), and allow communication between zones only through defined, controlled conduits. It is the formalization of an old instinct — the wellsite PLC should never be one flat network away from the accounting server.
Missing a term? This glossary grows with the questions we get from the field. If a word sent you here and you did not find it, email [email protected] and we will add it — and if you would rather see these concepts running live than defined, a guided demo of the Merobix platform covers most of this page in twenty minutes.
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