Gas detector
Gas detectors are used to sense the presence of gases, often for the purpose of determining whether combustible or otherwise harmful gases are present. There are many situations in which hazardous gases may accumulate in dangerous concentrations. In such cases health and safety regulations and prudence both require a system capable of detecting accumulations of hazardous gases before a hazardous situation exists. For example, smoke and fire alarms may detect the presence of any of various gases or particles in the air. Carbon dioxide is an example of one of such gases. Carbon dioxide is given off as a bi-product of combustion reactions. Carbon dioxide concentrations in air significantly increase if combustion is occurring in a closed space or nearby. The carbon dioxide given off disperse through the air, and the dispersion may occur more rapidly and in different directions than smoke or water vapor dispersion. The danger of these is becoming increasingly apparent, especially in industrial plants, mines, well-sealed homes and office buildings, recreational and other vehicles and other environments in which people are present for long periods Gas sensors are useful for safety monitoring, process monitoring and control, evaluation of gaseous product quality, environmental control and automotive applications. Infrared gas sensors are based on the principle of the selective absorption of infrared radiation by gases. Such gas sensors generally comprise one or more radiation sources, e.g. thermal radiators such as incandescent lamps, one or more absorption sections, wavelength-selecting elements (selective radiation filters) and one or more radiation detectors, which convert the optical signal into an electrical measurement signal. Non-dispersive infrared (NDIR) techniques utilizing the characteristic absorption bands of gases in the infrared have long been considered as one of the best methods for composite gas measurement. These techniques take advantage of the fact that various gases exhibit substantial absorption at specific wavelengths in the infrared radiation spectrum. Reduction gas detectors operate on the principle of flowing a gas stream to be analyzed through a heated bed of mercuric oxide (HgO). Electrolytic conductivity detectors usually provide an electrical signal that is functionally related to the presence of a selected component and typically aid in determining properties of electrolytes in solutions. Such devices often include electrode surfaces with a continuous phase liquid electrolyte in between the electrode surfaces. Metal oxide semiconductor (MOS) sensors are used to detect combustible gases. Combustible gases present a significant hazard in the work place. A MOS sensor typically comprises a sintered metal (tin, zinc, or iron) oxide film on an alumina or silica substrate, which surrounds a heater coil. In general, gas detectors often include a source of radiation, a sample chamber and a detector which uses transducers that respond to the presence of one or more selected gases to change their electrical characteristics to enable, by electrically monitoring such characteristics, the detection of the presence and concentration of the selected gas in an environment.
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