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Passive and active sensors

What is the difference between passive and active sensors? Professor Richard Mitchell explains more.
A small robot with a light sensor
© University of Reading

A passive sensor is one which just ‘listens’ to what is happening. Examples include:

  • A light sensor which detects if a light is shining on it
  • An infra-red sensor which detects the temperature of an object

An active sensor is one which transmits a signal into the environment and then measures the response that comes back.

One example is an ultrasonic system:

  • A pulse of ultrasound is emitted
  • If an object is in the way, the pulse is reflected back
  • The sensor detects it
  • The time taken between emission and detection gives an indication of the distance of the object.

Hence an active sensor has an actuator and a sensor. In the next step you can find out more about this in Richard’s demonstration on echo location.

© University of Reading
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