What is a Sensor?

“Sensor. Noun. A device that detects or measures a physical property and records, indicates, or otherwise responds to it.” – Google

A sensor detects physical variations in the world, e.g. light, temperature, radiowaves, sound, magnetic fields, vibration, particles (e.g. pollution, radiation) or objects (e.g. water droplets).

Humans contain Sensors

Humans and other creatures contain sensors: eyes, ears, nose, tongue, skin.  Humans are very good general-purpose sensors:

These sensors are sometimes used in sensor journalism, but so too are manmade sensors like cameras, motion detectors and thermometers.

In many situations, manmade sensors are more appropriate:  humans tend to fail the “dull, dirty, dangerous” test: their attention wanders on boring tasks, and it’s not fair to put them into dirty or dangerous situations where a manmade sensor would be more appropriate; they also can’t detect much of the physical world -e.g. radiowaves – without help, and their outputs aren’t always accurate enough for the task in hand.

Manmade Sensors are Old News

Manmade sensors convert common physical quantities (light, temperature etc) into measurements, actions or stimuli (sounds, light etc).  Manmade sensors have been designed and used for centuries, including:

Low-Tech Still Works

One area of journalism where sensors are commonly used is weather reporting.  At the low-tech end of modern weather recording is a Stevenson screen with manually-read instruments.  A Stevenson screen is a wooden box designed in 1864 to shelter a thermometer from direct weather (rain, snow, wind) and other objects (leaves, animals) that might damage the instruments inside it or bias readings from them. Stevenson screens are used for weather reporting worldwide, and contain instruments like:

Stevenson Screens are a good example of the care needed to obtain minimally-biased sensor readings.  The box and its positioning is standardized by the World Meteorological Organisation, to minimize instrument bias, e.g. all boxes are mounted 1.25m high to minimize ground temperature effects, louvred to minimize the effects of still air (e.g. overheating), and with doors opening North, to minimize reading errors from direct sunlight.

But Electronics can be Convenient

Each of the instruments above has an electronic equivalent, e.g. a sensor that can provide data remotely without a person needing to visit the Stevenson screen.  Digital sensors (sensors that convert physical quantities into electrical signals) are more recent, including digital cameras (Sasson 1975) and other sensors whose outputs can be sent to electronic storage, over wifi links or directly to computer processors.  We’ll talk more about these later.