Sensors (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: James Woodhouse
Reviewed by: Lucy Kirkham
Sensors
Sensors are input devices
They measure a physical property of their environment such as light levels, temperature or movement
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
A process where outputs are recycled and used as inputs, creating a continuous cycle is called a feedback loop
Examiner Tips and Tricks
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 |
D | Proximity |
A | Monitoring |
B | Control |
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