Multi-Criteria Detectors Weigh Several Fire Signatures Instead of One Threshold
A dual-sensor detector puts both an ionization and a photoelectric chamber in one housing so neither fire type is missed. A multi-criteria detector goes further: it combines smoke scattering with heat, and often with carbon monoxide, and applies an algorithm to the combination rather than a threshold to each channel. The point is not extra sensitivity, it is discrimination. Burnt toast produces particles without much carbon monoxide and without a rising temperature; a real smouldering fire produces all three in a characteristic order, so a rule that requires agreement across channels can be made both more sensitive and less prone to nuisance alarms at the same time, which no single-channel threshold can. Some devices add a second scattering angle or a second wavelength to separate steam and dust from combustion particles by particle size. The common confusion is that multi-criteria means the alarm needs every signature; usually it weights them, and one strong signature still alarms. After this Concept you can say why a multi-criteria device escapes the sensitivity-versus-nuisance bind that a single-channel detector cannot.
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A dual-sensor detector puts both an ionization and a photoelectric chamber in one housing so neither fire type is missed. A multi-criteria detector goes further: it combines smoke scattering with heat, and often with carbon monoxide, and applies an algorithm to the combination rather than a threshold to each channel. The point is not extra sensitivity, it is discrimination. Burnt toast produces particles without much carbon monoxide and without a rising temperature; a real smouldering fire produces all three in a characteristic order, so a rule that requires agreement across channels can be made both more sensitive and less prone to nuisance alarms at the same time, which no single-channel threshold can. Some devices add a second scattering angle or a second wavelength to separate steam and dust from combustion particles by particle size. The common confusion is that multi-criteria means the alarm needs every signature; usually it weights them, and one strong signature still alarms. After this Concept you can say why a multi-criteria device escapes the sensitivity-versus-nuisance bind that a single-channel detector cannot.
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