RM

optical and electronic instruments; namely, smoke density monitors, opacity monitors, dust density monitors, optical heads, and air purge units, the latter consisting of air purging ducts and air purging nozzles, used in conjunction with a motor whereby clean air is blown through such ducts and nozzles across th optical lenses of smoke density monitors, to prevent the deposit of contaminants upon such lenses, thereby enabling the proper function of such monitors; reflectors, shutters, junction boxes and parts therefor