Sensors — Input and Output Devices | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 3% of your exam marks.

stable

Rare

Stable3%

Typically tested as 'give one use of…' or 'describe how this sensor works' questions.

A sensor is an input device that measures a physical property of the environment and converts the measurement into a digital value the computer can use.

Monitoring systems vs control systems

Two related uses of sensors:

Monitoring system: the computer records and reports the readings, for example by showing them on a screen or raising an alert. It does not take action on its own. Example: a weather station that records temperature and humidity.
Control system: the computer acts on the readings, switching an output device on or off (or sending a signal to an actuator) to keep some condition stable. Example: a thermostat that turns on a heater when the temperature falls below the target.

A control system usually contains a feedback loop: the output (the heater) changes the condition the sensor is measuring (the temperature), which changes the reading the sensor sends, which changes whether the heater stays on. Feedback loops are covered in topic 15.

Common sensors

Sensor	Physical property	Where it is used
Acoustic	Loudness of sound	Noise pollution monitoring; security alarms; industrial machinery condition
Accelerometer	Acceleration, tilt, vibration	Smartphone orientation; car airbag deployment; pedometer step counting
Flow	Speed at which gas, liquid or powder is moving through a pipe	Water and gas meters; chemical pipelines
Gas	Presence of a specific gas (e.g. carbon monoxide, methane)	Home CO alarms; leak detection in industrial plants
Humidity	Water-vapour content of the air	Greenhouse climate control; museum preservation
Infrared	Heat radiation; or detecting whether an infrared beam is broken	Burglar alarms; thermal imaging cameras; automatic doors
Level	The height of a liquid in a tank	Petrol tank gauge; water tank; coolant level in a car
Light	Light intensity (brightness)	Automatic street lights; smartphone display auto-brightness; greenhouse blinds
Magnetic field	Strength and direction of a magnetic field	Anti-lock braking systems; reed switches on doors; compass apps
Moisture	Water content of soil or a material	Smart-irrigation systems; building damp detection
pH	Acidity or alkalinity of a liquid	Hydroponic farming; chemical process control; swimming-pool monitoring
Pressure	Force per unit area of a gas, liquid, or physical contact	Car tyre pressure monitoring; weather stations (barometric pressure); pipeline integrity
Proximity	Distance to a nearby object	Parking sensors when reversing; robotic obstacle avoidance; production-line counting
Temperature	How hot or cold something is	Central heating; ovens; refrigerators; weather stations; medical equipment