Sensors (Cambridge International IGCSE Computer Science)
Spec point — "3 (a) Understand what is meant by a sensor and the purposes of sensors (b) Identify the type of data captured by each sensor and understand when each sensor would be used, including selecting the most suitable sensor for a given context "
Sensors
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Sensors are input devices
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They measure a physical property of their environment such as light levels, temperature or movement
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Sensors can be used for monitoring systems and control systems
- A monitoring system tracks the state of a system, it gathers data and may issue warning messages
- A control system will control the system based upon the input from sensors
- For example, if the water temperature in a fish tank fell below the acceptable level, a control system would start up a heater
- The system will then continue to check the **water temperature readings **(outputs) and when they are within the acceptable range it will switch off the heater
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A process where outputs are recycled and used as inputs, creating a continuous cycle is called a** feedback loop**
Exam Hint
- You are likely to be given a scenario and asked to identify the sensors that would be used.
- The 14 sensors you need to be aware of are in the table below
| Sensor type | What it measures | Typical use |
|---|---|---|
| Acoustic | Sound levels | To detect changes in sound levels of industrial machinery To monitor noise pollution In security system to detect suspicious sounds |
| Accelerometer | Acceleration rate, tilt, vibration | Detecting sudden changes in vehicle movement and deploy safety features if needed In mobile phones to detect orientation of the device |
| Flow | Rate of gas, liquid or powder flow | Detect changes in the flow through pipes in water system |
| Gas | Presence of a gas e.g. carbon monoxide | Detect levels of gas in confined spaces Detect gas levels when fixing gas leaks |
| Humidity | Levels of water vapour | Monitor humidity in greenhouses |
| Infra-red | Detecting motion or a heat source | Security systems detecting intruders who break the beam Measures heat radiation of objects - used by emergency services to detect people |
| Level | Liquid levels | Detects levels of petrol in a car tank Detect levels of water in a water tank Detect a drop in water levels due to a leak |
| Light | Light levels | Automatically switching on lights when it gets dark (street lights, headlights) |
| Magnetic field | Presence and strength | Anti-lock braking system Monitoring rotating machinery such as turbines |
| Moisture | Presence and levels of moisture | Monitoring moisture in the soil Monitoring dampness in buildings |
| pH | Acidity or alkaline | Monitoring soil to ensure optimum growing conditions Monitor ph levels in chemical processes |
| Pressure | Gas, liquid or physical pressure | Monitoring tyre pressure Monitoring pressure in pipes during the manufacturing process |
| Proximity | Distance | Monitoring the position of objects in robotics Used in safety systems to prevent objects from colliding |
| Temperature | Temperature in Celsius, Fahrenheit or Kelvin | Used to maintain temperature in swimming pools Used to control temperature in chemical processes |
Worked Example What type of sensor would be used to help drivers when reversing? [1]
A Motion B Infra-red C Light D Proximity Is this a monitoring system or a control system? [1]
A Monitoring B Control Answer
A Motion B Infra-red C Light Final answer: D Final answer: Proximity
Final answer: A Final answer: Monitoring B Control
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