Glossary of Control Systems in Technology and Aviation

Control System

A control system is a configuration of devices, algorithms, and networks that manages, directs, or regulates the behavior and operation of other systems or processes. It receives input signals (such as sensor readings), processes them according to programmed logic or mathematical models, and issues output commands to achieve or maintain a desired outcome. Control systems are fundamental to aviation (for flight stability and safety), industrial automation, robotics, energy management, and myriad other sectors.

Formally, control systems may be automatic (requiring no direct human intervention) or manual (relying on operator input), but the modern trend, especially in safety-critical applications like aviation and energy, is toward increasing automation and autonomy. The core function is to maintain a process variable—such as altitude, engine speed, temperature, or pressure—at a setpoint, even as external disturbances or internal changes occur.

There are two principal types:

• Open-loop control systems: Operate solely on predefined logic or time schedules, without measuring actual output for correction.
• Closed-loop (feedback) control systems: Continuously monitor outputs and compare them to setpoints, adjusting commands as needed to minimize errors.

Components typically include sensors (for measurement), controllers (for computation and logic), actuators (to implement changes), and human-machine interfaces (HMIs) (for operator supervision and intervention). Communication networks connect these elements, enabling reliable, real-time data exchange, especially in distributed or networked environments.

Control systems are the backbone of modern technology, evolving rapidly with the integration of digital computation, AI, and robust networking, pushing the boundaries of automation, efficiency, safety, and remote management.

Sensor

A sensor is a physical device that detects and measures a property (such as temperature, pressure, position, or chemical composition) and converts it into a signal readable by a control system. Sensors provide the raw data essential for monitoring processes, enabling precision and safety in automation.

Aviation examples:

• Pitot tubes and air data probes (airspeed, altitude)
• Inertial Measurement Units (IMUs) for attitude and movement
• Temperature and pressure sensors in engines and cabins

Industry examples:

• Thermocouples, RTDs (temperature)
• Strain gauges, piezoelectric transducers (force, pressure)
• Proximity and position sensors (robotics, automation)

In critical systems, sensors are often duplicated (redundant) and equipped with self-diagnostics to detect faults, as per ICAO and industry standards. Modern sensors may include built-in processing, networking (ARINC 429, CAN bus), and advanced calibration, ensuring resilience in harsh environments.

Controller

A controller is the processing element of a control system. It receives sensor data, compares it to desired setpoints, and determines the necessary output to actuators. Controllers can be simple analog circuits, programmable logic controllers (PLCs), microcontrollers, or sophisticated embedded computers.

Aviation examples:

• Flight management systems (FMS)
• Autopilot and fly-by-wire computers
• Engine control units (ECU/FADEC)

Industry examples:

• PLCs in assembly lines
• Process controllers in chemical plants

Controllers implement various algorithms:

• PID (Proportional-Integral-Derivative) for balancing error correction
• Model-based or adaptive control for complex, changing environments

Safety-critical systems use redundant controllers with fail-operational design, as specified by DO-178C or IEC 61508 standards. Controllers may include cybersecurity features and remote diagnostics for secure, reliable operation.

Actuator

An actuator is a device that converts the controller’s output signals into physical action, affecting the process or machine.

Aviation examples:

• Servomotors for control surfaces (elevators, ailerons, rudder)
• Hydraulic actuators (landing gear, flaps)
• Electric actuators (valves, environmental controls)

Industry examples:

• Electric motors (conveyors, pumps)
• Solenoid valves (fluid control)
• Piezoelectric actuators (precision tasks)

Actuators are chosen for response speed, force, precision, reliability, and environmental constraints. Safety is paramount: redundant actuators and position feedback are standard in aviation and critical infrastructure.

Human-Machine Interface (HMI)

A Human-Machine Interface (HMI) is the platform through which humans interact with automated systems. It provides visualizations, controls, alerts, and real-time process data.

Aviation examples:

• Cockpit flight displays (PFD, MFD, EICAS)
• Touchscreen controls, head-up displays, voice interfaces

Industry examples:

• Touchscreen control panels on machinery
• SCADA dashboards for process monitoring

HMI design prioritizes ergonomics and human factors, with clear alerting, intuitive controls, and protection against cyber threats. Remote access HMIs are increasingly common, demanding strong security.

Communication Network

A communication network connects the components of control systems (sensors, controllers, actuators, HMIs), enabling reliable data exchange.

Aviation protocols:

• ARINC 429/629 (deterministic avionics data buses)
• CAN bus
• ARINC 664/AFDX (Ethernet-based, high-bandwidth, redundant)

Industrial protocols:

• Profibus, Modbus, Ethernet/IP, OPC UA

Robustness, security, redundancy, and real-time performance are essential. In IoT and networked environments, advanced management and cybersecurity are critical.

Open-Loop Control System

An open-loop control system operates on predefined logic or timed instructions, without measuring or correcting its actual output. It assumes predictable system behavior.

Examples:

• Timer-based deicing systems in aviation
• Washing machines, toasters

Open-loop systems are simple and cost-effective but cannot adapt to disturbances or variations. They are best for non-critical, predictable applications.

Closed-Loop (Feedback) Control System

A closed-loop (feedback) control system continuously measures its output, compares it to a setpoint, and adjusts its input to minimize error.

Aviation examples:

• Autopilots adjusting flight path based on sensor feedback
• Engine control units maintaining thrust

Industry examples:

• Temperature controllers, voltage regulators

Closed-loop control ensures accuracy, adaptability, and stability, essential for dynamic or safety-critical environments.

SISO and MIMO

SISO (Single Input Single Output) systems control one input and one output.
MIMO (Multiple Input Multiple Output) systems handle multiple inputs and outputs, managing complex interactions.

Aviation MIMO example:

• Coordinated flight control (pitch, roll, yaw, throttle)

MIMO systems require advanced modeling and control strategies, such as state-space or model predictive control.

Embedded Control System

An embedded control system is a dedicated controller integrated within a larger device, performing specific real-time functions.

Aviation examples:

• FADEC for engines
• Cabin pressure controllers

Design features:

• Optimized for size, weight, power
• Reliable under strict certification (DO-178C)

Embedded systems form the backbone of modern avionics, consumer products, and industrial automation.

Distributed Control System (DCS) and Networked Control System (NCS)

A Distributed Control System (DCS) uses multiple controllers distributed across a plant or facility, coordinating via a network.

Industry examples:

• Refineries, power plants, airport energy management

A Networked Control System (NCS) is any control system where components communicate over networks, including wireless or Ethernet-based systems, enabling remote monitoring and distributed intelligence.

SCADA (Supervisory Control and Data Acquisition)

SCADA systems provide supervisory control and centralized data acquisition for geographically dispersed assets.

Aviation examples:

• Airport lighting, HVAC, baggage handling

Features:

• Real-time monitoring, alarms, remote operation
• Secure communication and robust data logging

SCADA is essential for operational efficiency and safety in large infrastructure.

Feedback

Feedback is the process of sending a portion of the output back to the controller for real-time comparison and adjustment.

• Negative feedback stabilizes systems (e.g., thermostat)
• Positive feedback amplifies changes (risky if not controlled)

Feedback is vital for closed-loop control, ensuring accuracy and robustness.

This glossary provides foundational definitions for core concepts in control systems as applied in aviation, technology, and industry. For further details or custom solutions, contact us or schedule a demo .