Booker Hill Projects Ltd Glossary Of Control Engineering

Stepping into the world of control engineering can feel a bit like learning a new language. Terms such as feedback loops, PID controllers, and transfer functions get thrown around quickly, and before long it’s easy to feel overwhelmed. But control engineering doesn’t have to be intimidating. With the right explanations—and a handy glossary—you can build a strong foundation that makes everything else much easier to understand.

This glossary is designed specifically for beginners who want clear, simple definitions without the jargon. Whether you’re a student, a new engineer, or just curious about how automated systems work, this guide will help you become more confident with the terminology you’ll encounter in textbooks, tutorials, and real-world applications. Think of it as your quick‑reference companion on your journey into control systems.

Let’s break down the buzzwords and start making sense of how machines, processes, and feedback come together to create the controlled, stable systems we rely on every day.

🧭 Foundations of Control Systems

• Control System — A system that manages, commands, directs, or regulates the behaviour of other devices or systems using control loops.

• Feedback — Information returned to the controller about the actual output, used to correct deviations.

• Setpoint (SP) — The desired value a control system aims to maintain (e.g., temperature, pressure).

• Process Variable (PV) — The actual measured value of the controlled parameter.

• Manipulated Variable (MV) — The variable the controller adjusts to influence the process (e.g., valve position).

• Disturbance — An external factor that affects the process and causes deviation from the setpoint.

• Stability — The ability of a control system to return to equilibrium after a disturbance.

  
  

⚙️ Controllers & Algorithms

• PID Controller — A controller using proportional, integral, and derivative actions to minimise error.

• Proportional Control (P) — Corrects error in proportion to its magnitude.

• Integral Control (I) — Eliminates steady‑state error by integrating past errors.

• Derivative Control (D) — Predicts future error based on its rate of change.

• Feedforward Control — Adjusts the process based on known disturbances before they affect the output.

• Cascade Control — A control structure with a primary and secondary loop for improved performance. I.e. Level ➡️ Flow SP ➡️ PV MP Speed.

• Ratio Control — Maintains a fixed ratio between two process variables (e.g., fuel/air).

• Adaptive Control — Automatically adjusts controller parameters in real time.

• Model Predictive Control (MPC) — Uses a dynamic model to predict future behaviour and optimise control actions.

  
  

🏭 Industrial Automation Hardware

• PLC (Programmable Logic Controller) — Rugged industrial computer used for automation and control.

• PAC (Programmable Automation Controller) — A more powerful, flexible controller combining PLC reliability with PC‑style processing.

• DCS (Distributed Control System) — A networked control architecture used in large, continuous processes (e.g., chemical plants).

• RTU (Remote Terminal Unit) — Field device used in remote monitoring and SCADA systems.

• HMI (Human–Machine Interface) — Screens or panels operators use to interact with control systems.

• SCADA (Supervisory Control and Data Acquisition) — System for monitoring, controlling, and collecting data from remote equipment.

• I/O (Input/Output) — Interfaces that connect sensors and actuators to controllers.

  
  

  • AI (Analogue Input) — A variable electrical signal (like 0–10 V or 4–20 mA) sent into a controller to represent measured values such as temperature or pressure.

  • DI (Digital Input) — A two‑state signal (ON/OFF or 1/0) sent into a controller from devices like switches or sensors.

  • AO (Analogue Output) — A variable signal sent from a controller to adjust devices such as valves or speed drives.

  • DO (Digital Output) — A simple ON/OFF signal sent from a controller to operate equipment like relays, solenoids, or indicator lights.

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• Servo Motor — High‑precision motor used in motion control applications.

• VFD (Variable Frequency Drive) AKA VSD (Variable Speed Drive) — Controls AC motor speed by varying frequency and voltage.

  
  

🔌 Sensors, Actuators & Field Devices

• Transmitter — Converts sensor signals into standardised outputs (e.g., 4–20 mA).

• Thermocouple — Temperature sensor using voltage generated by two dissimilar metals.

• RTD (Resistance Temperature Detector) — Temperature sensor using resistance changes in metal.

• Flowmeter — Device measuring fluid flow rate (e.g., Coriolis, magnetic, turbine).

• Pressure Transducer — Converts pressure into an electrical signal.

• Control Valve — Modulates flow using a valve body, actuator, and positioner.

• Actuator — Mechanism that moves or controls a device (electric, pneumatic, hydraulic).

• Solenoid — An electromechanical device that uses electricity to move a metal plunger, commonly used to operate valves or switches.

• Limit Switch — Detects the presence or position of an object.

  
  

🌐 Industrial Communication & Networking

• OPC UA — Platform‑independent communication standard for secure industrial interoperability.

• Fieldbus — Digital communication network for industrial automation (e.g., Profibus, Foundation Fieldbus, Ethernet IP).

• EtherCAT — High‑performance Ethernet‑based fieldbus for motion control.

• Modbus — Widely used serial/Ethernet communication protocol.

• IIoT (Industrial Internet of Things) — Connected industrial devices enabling data‑driven operations.

• Edge Computing — Processing data near the source rather than in the cloud.

  
  

📊 Modelling, Simulation & Analysis

• Transfer Function — Mathematical representation of a system’s input–output behaviour.

• State‑Space Model — System representation using state variables and matrices.

• Time Constant — Measure of how quickly a system responds to changes.

• Bode Plot — Frequency‑response graph showing magnitude and phase.

• Nyquist Plot — Graph used to assess stability in the frequency domain.

• Root Locus — Plot showing how system poles move with controller gain.

• HIL (Hardware‑in‑the‑Loop) — Testing method combining real hardware with simulated systems.

  
  

🛠️ Engineering Workflow & Safety

• Commissioning — Testing and validating a control system before operation.

• FAT (Factory Acceptance Test) — Testing equipment at the vendor’s site before delivery.

• HAZOP (Hazard and Operability Study) — A structured, systematic review used to identify potential hazards and operational issues in a process or system by examining how deviations from normal conditions could lead to risks.

• SAT (Site Acceptance Test) — Testing equipment after installation and commissioning at the customer’s site.

• Redundancy — Duplicate components to ensure reliability (e.g., dual PLCs).

• SIL (Safety Integrity Level) — Risk‑reduction rating for safety systems.

• LOPA (Layer of Protection Analysis) — Method for assessing process risk.

• Alarm Management — Designing alarms to avoid nuisance and ensure operator effectiveness.

  
  

🧩 Modern Digital & Data Concepts

• Digital Twin — Virtual model of a physical system used for simulation and optimisation.

• Predictive Maintenance — Using data analytics to predict equipment failures.

• Machine Learning — Algorithms that learn patterns from data to improve control or prediction.

• Big Data — Large datasets generated by sensors, SCADA, and IIoT devices.

• Cloud SCADA — SCADA systems hosted on cloud platforms for remote access and scalability.

• Dashboard — visual display that shows key process data—such as temperatures, pressures, alarms, and equipment status—to help operators quickly monitor and understand system performance.