Gas Sensors. How Stuff Works

Gas Sensors are devices which detects the presence of gases in an area. These are used for safety purposes to activate alarm systems as warning measure or to shut down a machinery. Gas detectors are used to detect different kinds of gases like combustible, flammable and toxic gases. These are also find application in the detection of oxygen depletion in an area. As the gas sensors measure a particular concentration of gas, the sensor responds to a calibrated gas and serves as a point or scale. As the level of gas increases above the sensor’s calibrated level, the alarm will be activated. Individual sensors are usually used to detect particular gases, but sensors capable of detecting various kinds gases are also available.
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Laser based Alarm System. Sensor Circuit.17

It is easy to construct a Laser based Relay activator to operate Alarm systems or to switch on CCTV or Auto Camera when there is any attempt of theft. It can be used to guard, doors, entry passages etc. The circuit uses Laser beam so that the range of the circuit is more than 10 meters and there is no false triggering.

Laser diode is similar to LED and emits Monochromatic narrow laser beam that passes long distance through air. The Laser diode requires 3 volts and around 100 mA current for getting maximum range. So the current limiting resistor must be selected as per the range. A China make low cost laser torch can be used for the purpose.
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