Fume detector and alarm system

摘要: A fume detector including a gas sensor having heater element and variable impedance associated therewith whose decreases in the presence of toxic gases or fumes, decrease free oxygen an atmosphere being monitored. load resistor series circuit with pair connected potentiometers parallel form Wheatstone bridge. first voltage comparator to one reference provides signal when supply below predetermined level. second other potentiometer junction between fails open condition. third across bridge condition exists. The first, outputs are commonly input fourth comparator. warning device is output energized any signals comparators falls