Industrial Automation Glossary

Plain-English definitions of common terms in instrumentation, control systems and manufacturing IT. Terms link to our full tutorials where you can learn more. Use your browser’s find function (Ctrl+F) to jump to a term.

Numbers

4-20 mA — The most common analog signal for process instruments. The measured range maps to 4-20 mA; the “live zero” at 4 mA makes it possible to detect a broken wire. Try the 4-20 mA calculator.

A

Actuator — A device that moves or controls a mechanism, such as a pneumatic valve actuator or an electric motor.

Alarm — A notification to the operator that a condition requires a response. Good alarm systems follow ISA-18.2 and avoid nuisance alarms. See setting up SCADA alarms.

Alarm flooding — When so many alarms occur in a short period that operators cannot respond to them effectively, often during a plant upset.

Analog input (AI) / analog output (AO) — Controller I/O channels for continuous signals such as 4-20 mA or 0-10 V.

Asset management — Tracking the condition, configuration and maintenance history of plant equipment and instruments.

Availability (OEE) — The share of planned production time that equipment is actually running. See the OEE calculator.

B

Batch process — Production in discrete quantities following a recipe, common in pharmaceuticals, food and specialty chemicals. Governed by ISA-88.

Bumpless transfer — Switching a controller between manual and automatic without a sudden jump in output.

Bus topology — A network layout where devices share one communication line. See SCADA network topologies.

C

Calibration — Comparing an instrument against a reference standard and adjusting it so its readings are correct. See calibration and standardization.

Cascade control — Two nested control loops where the output of the primary (outer) controller sets the setpoint of the secondary (inner) controller.

CMMS — Computerized Maintenance Management System, used to plan and record maintenance work.

Commissioning — Testing and bringing a new or modified system into operation, including loop checks and functional tests.

Control loop — The combination of a measurement, a controller and a final control element working to hold a process variable at its setpoint. See PID control.

Control valve — A valve positioned by a controller to regulate flow, pressure, temperature or level.

Coriolis flowmeter — A meter that measures mass flow directly from the twisting of vibrating tubes. See mass flowmeters.

CPU — The processor module of a PLC that executes the control program. See PLC components.

D

Data historian — A database optimized for storing and retrieving time-series process data. See DCS database servers.

Dead time — The delay between a change in controller output and the first measurable response of the process.

Derivative action (D) — The part of a PID controller that responds to the rate of change of the error.

Differential pressure (DP) — The difference between two pressures; used to infer flow and level. See the DP level calculator.

Digital input (DI) / digital output (DO) — On/off I/O channels, such as limit switches and motor start commands.

Digital twin — A virtual model of a physical asset or process, updated with real data, used for simulation, optimization and training.

Displacer — A level instrument that measures the change in buoyant force on a partially submerged body. See float, displacer and DP level.

DCS — Distributed Control System, a plant-wide control system with controllers distributed across the process, common in continuous process industries. See what is a DCS.

DMZ (industrial) — A buffer network between plant (OT) and business (IT) networks that controls data flows between them.

E

Edge computing — Processing data close to the equipment rather than in a central data center or cloud. See IIoT.

Electromagnetic flowmeter (magmeter) — A flowmeter that measures the voltage induced when a conductive liquid flows through a magnetic field. See magnetic and ultrasonic flowmeters.

Electronic batch record (EBR) — A digital record of how a batch was produced, used in regulated industries such as pharmaceuticals instead of paper batch records.

ERP — Enterprise Resource Planning, business software for finance, orders, purchasing and planning (ISA-95 Level 4).

Ethernet/IP — An industrial Ethernet protocol based on the Common Industrial Protocol (CIP). See industrial protocols.

F

Fail-safe — A design in which a failure leads to a safe state, such as a valve that closes on loss of air.

FAT / SAT — Factory Acceptance Test and Site Acceptance Test: formal tests of a system at the supplier’s facility and again after installation on site.

Feedforward control — Adjusting the controller output based on a measured disturbance before it affects the process variable.

Field device — An instrument or actuator installed in the process, such as a transmitter or control valve. See DCS field devices.

Fieldbus — A digital network connecting field devices to controllers, such as PROFIBUS or Foundation Fieldbus.

Function Block Diagram (FBD) — A graphical IEC 61131-3 PLC language built from connected function blocks. See PLC programming languages.

G

Gateway — A device that translates between two communication protocols, for example Modbus RTU to OPC UA.

Gauge pressure — Pressure measured relative to atmospheric pressure. See absolute vs gauge vs differential pressure.

Genealogy — The record of which materials, lots and process steps went into a finished product; a core MES function.

H

HART — A protocol that adds digital communication on top of a 4-20 mA signal for configuration and diagnostics.

HMI — Human-Machine Interface, the screens operators use to monitor and control the process. See SCADA HMI.

Hysteresis — The difference in an instrument’s output depending on whether the input is increasing or decreasing.

I

I/O module — Controller hardware that connects field signals to the controller. See DCS controllers and I/O.

IEC 61131-3 — The international standard defining PLC programming languages.

IEC 62443 — The international series of standards for industrial automation cybersecurity. See ISA-99.

IIoT — Industrial Internet of Things, connecting industrial devices and systems to share data. See IIoT explained.

Integral action (I) — The part of a PID controller that accumulates error over time to eliminate offset.

Integral windup — Excessive build-up of the integral term while the controller output is saturated, causing overshoot.

Interlock — Logic that prevents or forces an action to protect people, equipment or product, such as stopping a pump on low suction pressure.

Intrinsic safety (IS) — A protection technique that limits electrical energy so it cannot ignite a hazardous atmosphere.

ISA-88 — The standard for batch control, defining physical, procedural and recipe models. See ISA-88.

ISA-95 — The standard for integrating enterprise and control systems, defining levels 0-4. See ISA-95.

L

Ladder Diagram (LD) — A PLC programming language resembling relay wiring diagrams.

Level transmitter — An instrument that measures the level of liquid or solids in a vessel. See radar vs ultrasonic level sensors.

Loop check — Verifying during commissioning that each instrument signal reaches the correct controller input with the correct scaling.

LRV / URV — Lower and upper range values of a transmitter, corresponding to 4 mA and 20 mA.

M

MES — Manufacturing Execution System, software that manages and tracks production on the shop floor (ISA-95 Level 3). See what is MES.

Modbus — A simple, widely used open protocol for industrial communication, available as RTU (serial) and TCP (Ethernet).

MQTT — A lightweight publish/subscribe messaging protocol widely used in IIoT.

MTBF / MTTR — Mean Time Between Failures and Mean Time To Repair, key reliability metrics.

O

OEE — Overall Equipment Effectiveness = Availability × Performance × Quality. See the OEE calculator.

OPC UA — A secure, platform-independent standard for industrial data exchange with a rich information model.

OT — Operational Technology: the hardware and software that monitor and control physical processes.

Offset — A steady-state difference between setpoint and process variable, typical of proportional-only control.

P

P&ID — Piping and Instrumentation Diagram, showing process equipment, piping, instruments and control loops.

Performance (OEE) — Actual production speed compared with the ideal speed while running.

PID — Proportional-Integral-Derivative, the most common feedback control algorithm. See PID control explained.

PLC — Programmable Logic Controller, an industrial computer for real-time control of machines and processes. See what is a PLC.

Pressure transmitter — An instrument that converts pressure into an electrical signal. See pressure transmitters.

Process variable (PV) — The measured quantity being controlled, such as temperature or flow.

PROFIBUS / PROFINET — Fieldbus and industrial Ethernet protocols from PROFIBUS & PROFINET International.

Proportional band (PB) — An alternative way of expressing controller gain: PB % = 100 ÷ gain.

R

Redundancy — Duplicating critical components, such as controllers, networks or power supplies, so the system keeps running if one fails.

Repeatability — The ability of an instrument to give the same reading for the same input under the same conditions. See accuracy, precision and repeatability.

RTD — Resistance Temperature Detector, usually platinum (Pt100 or Pt1000). See the RTD calculator.

RTU — Remote Terminal Unit, a field device that collects data and communicates with SCADA over long distances. See RTUs in SCADA.

S

Safety Instrumented System (SIS) — An independent system that takes the process to a safe state when dangerous conditions are detected (IEC 61511).

Scan cycle — The repeating cycle in which a PLC reads inputs, executes its program and updates outputs. See how PLCs work.

SCADA — Supervisory Control and Data Acquisition, systems for monitoring and controlling distributed processes. See what is SCADA.

Sequential Function Chart (SFC) — An IEC 61131-3 language for describing sequences of steps and transitions.

Setpoint (SP) — The target value for a controlled variable.

SIL — Safety Integrity Level (1-4), a measure of the risk reduction provided by a safety function.

Signal conditioning — Processing a sensor signal (amplifying, filtering, isolating, linearizing) so it can be measured accurately. See signal conditioning.

Smart transmitter — A microprocessor-based transmitter with digital communication and diagnostics.

SPC — Statistical Process Control, using control charts to monitor process variation. See manufacturing analytics.

Split-range control — One controller output driving two or more final elements over different parts of its range.

Stiction — Static friction in a control valve that makes it stick and then jump, often causing oscillation.

Structured Text (ST) — A high-level, text-based IEC 61131-3 PLC language similar to Pascal.

T

Tag — A named data point in a control system, such as a process value, setpoint or alarm.

Thermocouple — A temperature sensor made of two dissimilar metals that produces a voltage proportional to temperature difference. See thermocouple types.

Time constant — For a first-order process, the time to reach 63.2% of the final change after the dead time.

Traceability — The ability to trace a product’s history, materials and process conditions. See MES traceability.

Transmitter — An instrument that converts a measurement into a standard signal for transmission to a controller.

U

Unified Namespace (UNS) — An architecture where all systems publish their current state to a central, hierarchical data hub, often built on MQTT.

V

VFD — Variable Frequency Drive, which controls motor speed by varying supply frequency.

Vortex flowmeter — A flowmeter that counts vortices shed by a bluff body placed in the flow.

W

Wet leg — A liquid-filled reference line on a DP level transmitter, used when vapors would condense in the line.

Watchdog timer — A timer in a PLC or controller that faults the CPU if the program scan takes too long, protecting against runaway or stuck programs.

Work order — An instruction to produce a quantity of product (production) or perform a task (maintenance).

Z

Zero suppression / elevation — Calibration adjustments to a DP transmitter’s range to account for liquid in impulse lines or wet legs.

Zones and conduits — The IEC 62443 approach to segmenting industrial networks into security zones connected by controlled conduits.