In simple terms
A friendly intro before the formal notes — no formulas yet.
The Smart Thermostat
Control systems are the brains behind automated devices, from your home's heating to a factory robot. They use sensors to perceive the world, a processor to make decisions, and actuators to perform actions.
Imagine you are cooking. You look at the food to see if it's cooked (your eyes are sensors). You decide it needs five more minutes (your brain is the processor). You turn the oven dial down (your hand is the actuator). After a few minutes, you check again (this is feedback), creating a closed-loop system to get the perfect result. Without checking again, it would be an open-loop system – you'd just be guessing.
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A sensor, like a thermometer, measures a physical property from the environment, converting it into an electrical signal.
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A processor compares the sensor's reading to a pre-defined target value, known as the setpoint.
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Based on the difference, the processor commands an actuator, such as a heater or a fan, to take action.
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The sensor continuously monitors the environment, feeding new data back to the processor, creating a feedback loop for ongoing adjustments.
Explore the concept
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Full topic notes
Formal explanation with the rigour you need for the exam.
Core Components of a Control System
Every control system, regardless of its complexity, is built upon three fundamental types of components that work in a sequence: sensors, a processor, and actuators. Understanding the distinct role of each is crucial to analysing any automated system.
Sensors: The 'senses' of the system. They measure physical quantities from the environment like temperature, humidity, light level, or speed. They convert this physical measurement into an electrical signal.
Processor: The 'brain' of the system. This is typically a microcontroller or a dedicated computer. It reads the signal from the sensor, processes this information according to its programming (e.g., comparing it to a setpoint), and decides what action to take.
Actuators: The 'muscles' of the system. They receive a command signal from the processor and convert it into a physical action. Examples include motors, pumps, heaters, valves, and speakers.
Bridging Worlds: Analogue and Digital Signals
The physical world is inherently analogue; properties like temperature or pressure can have any value within a continuous range. However, the processors at the heart of control systems are digital, working with discrete values (0s and 1s). This creates a need for conversion between the two domains.
Physical Property
An Analogue-to-Digital Converter (ADC) samples the continuous analogue signal from the sensor at regular intervals and quantises it into a digital representation. Conversely, a Digital-to-Analogue Converter (DAC) takes the digital command from the processor and generates a corresponding analogue voltage or current to drive an actuator.
Feedback: Open vs. Closed Loops
The most significant distinction in control systems is the presence or absence of feedback. Feedback is the mechanism by which a system's output is used to modify its input, allowing for self-regulation. This leads to two categories of systems: open-loop and closed-loop.
Open-Loop Systems: These systems do not use feedback. The control action is independent of the output. They are simpler and cheaper but can be inaccurate and unable to compensate for disturbances. A microwave oven operating on a timer is an open-loop system; it runs for the set time regardless of how cooked the food is.
Closed-Loop Systems: These systems use feedback. The output is measured by a sensor and compared to the setpoint. The difference (error) is used to adjust the control action. These systems are more complex and expensive but are highly accurate and stable. A car's cruise control is a classic example; it constantly adjusts the engine throttle to maintain a constant speed despite hills or wind.
Worked examples
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A domestic central heating system uses a thermostat to maintain a comfortable room temperature. Analyse this as a closed-loop control system. Identify the setpoint, sensor, processor, actuator, and describe the feedback loop. [5 marks]
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Here is a possible mark-scheme breakdown:
An automated irrigation system for a farm needs to maintain optimal soil moisture. Describe a closed-loop system to achieve this, identifying the necessary components and explaining the process, including signal conversion. [6 marks]
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Here is a possible mark-scheme breakdown:
How it all connects
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Glossary
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Quick check
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Revision flashcards
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What is a control system?
A system that manages, commands, directs, or regulates the behaviour of other devices or systems to achieve a desired result. It consists of sensors, a processor, and actuators.
Key takeaways
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Sensors: The 'senses' of the system. They measure physical quantities from the environment like temperature, humidity, light level, or speed. They convert this physical measurement into an electrical signal.
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Processor: The 'brain' of the system. This is typically a microcontroller or a dedicated computer. It reads the signal from the sensor, processes this information according to its programming (e.g., comparing it to a setpoint), and decides what action to take.
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Actuators: The 'muscles' of the system. They receive a command signal from the processor and convert it into a physical action. Examples include motors, pumps, heaters, valves, and speakers.
Practice — then mark it
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Practice Questions on Control Systems
Practice Questions on Control Systems
Extra simulations & links
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Checkpoint
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