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 and when they are within the acceptable range it will switch off the heater
- This process of the outputs affecting the following set of input values received from the sensors is called a feedback loop
Exam Tip
- 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
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Acoustic |
Sound levels |
To detect changes in sound levels of industrial machinery To monitor noise pollution In security system to detect suspicious sounds |
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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 |
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Flow |
Rate of gas, liquid or powder flow |
Detect changes in the flow through pipes in water system |
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Gas |
Presence of a gas e.g. carbon monoxide |
Detect levels of gas in confined spaces Detect gas levels when fixing gas leaks |
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Humidity |
Levels of water vapour |
Monitor humidity in greenhouses |
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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 |
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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 |
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Light |
Light levels |
Automatically switching on lights when it gets dark (street lights, headlights) |
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Magnetic field |
Presence and strength |
Anti-lock braking system Monitoring rotating machinery such as turbines |
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Moisture |
Presence and levels of moisture |
Monitoring moisture in soil Monitoring damp in buildings |
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pH |
Acidity or alkaline |
Monitoring soil to ensure optimum growing conditions Monitor pHlevels in chemical processes |
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Pressure |
Gas, liquid or physical pressure |
Monitoring tyre pressure Monitoring pressure in pipes during manufacturing process |
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Proximity |
Distance |
Monitoring position of objects in robotics Used in safety systems to prevent objects colliding |
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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]
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A |
Motion |
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B |
Infra-red |
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C |
Light |
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D |
Proximity |
- D [1]
- A proximity sensor would be used to monitor how close the car was to objects. It would then sound a warning alarm when the proximity is below a certain value (meaning the car is too close to an object)
Is this a monitoring system or a control system?
[1]
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A |
Monitoring |
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B |
Control |
- A [1]
- The reversing warning system is a monitoring system. It indicates to the user when the car is too close to an object but it does not stop the car automatically
