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A sensor measures a physical property and supplies data to a computer. A processor compares readings with a rule or stored threshold. An actuator then changes a physical condition. Sensors provide input; actuators provide output.
Sensor | Physical property / suitable application |
|---|---|
Acoustic | Sound level, such as noise monitoring |
Accelerometer | Acceleration, such as detecting a fall |
Flow | Rate of fluid movement through a pipe |
Gas | Concentration/presence of a gas, such as a leak |
Humidity | Water vapour in air, such as a greenhouse atmosphere |
Infra-red | Infra-red radiation, such as detecting a warm body |
Level | Height of liquid in a tank |
Light | Light intensity, such as automatic lighting |
Magnetic field | Magnetic field, such as a door-position detector |
Moisture | Water content in a material, such as soil |
pH | Acidity/alkalinity, such as nutrient solution |
Pressure | Force per area, such as tyre pressure |
Proximity | Presence of a nearby object, such as parking assistance |
Temperature | Temperature, such as a freezer |
Worked decision: irrigation
Air may be humid while soil is dry. Choose a soil moisture sensor to decide when plants need water. A humidity sensor answers a different question. Read the moisture value, compare with the required threshold, operate the valve actuator, and keep reading so watering stops when appropriate.
An analogue sensor varies continuously. An analogue-to-digital converter (ADC) converts its signal into a digital reading for the processor. A digital sensor may incorporate this conversion; do not assume every external sensor needs a separate ADC box.
Independent application
Choose sensors for a water tank's height, its pipe's flow rate, and the acidity of its contents. Explain why one sensor cannot directly measure all three quantities.
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Transfer: Sensor selection
Transfer: Sensor selection
- Rate of change of motion: [Space 1]
- Vehicle approaching an obstacle: [Space 2]
- Change in a magnetic field: [Space 3]
- Signal conversion needed for an analogue reading: [Space 4]
Interactive exercises for Module 2 and beyond require an active plan.