What is a Gas Sensor?

Fundamentals
Gas sensors are commonly used to detect toxic or explosive gasses and measure their concentration (Getty Images)

Gas sensors (also known as gas detectors) are electronic devices that detect and identify different types of gasses. They are commonly used to detect toxic or explosive gasses and measure gas concentration. Gas sensors are employed in factories and manufacturing facilities to identify gas leaks, and to detect smoke and carbon monoxide in homes. Gas sensors vary widely in size (portable and fixed), range, and sensing ability. They are often part of a larger embedded system, such as hazmat and security systems, and they are normally connected to an audible alarm or interface. Because gas sensors are constantly interacting with air and other gasses, they have to be calibrated more often than many other types of sensors. 

Depending on their intended environments and functions, the physical makeup and sensing process can vary notably between sensors. One of the most commonly used gas sensors for toxic identification and smoke detection is the metal oxide based gas sensor. This type of sensor employs a chemiresistor which comes in contact and reacts with target gasses. Metal oxide gas sensors increase their electrical resistance as they come into contact with gasses such as carbon monoxide, hydrogen, methane, and butane. Most home based smoke detection systems are oxide based sensors.

Infrared gas sensor scheme
Infrared gas sensor scheme. (EnggCyclopedia)

Infrared point sensors measure the absorption and reflection of IR light when interacting with gasses. As a type of optical sensor, IR point sensors are comprised of multiple infrared emitters and photodiodes that determine the concentration and type of gas in a given space. The same principle is used with ultrasonic gas sensors, but instead of IR, ultrasonic sensors use sound waves to determine concentration. Caliometric sensors are specifically designed to interact with explosive gasses such as hydrogen and methane. These sensors react with the explosive gasses to create a corresponding amount of heat.

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