MINIATURE PHOTOELECTRIC SENSING CHAMBER

A low profile, low volume smoke chamber displaces a light source, such as a light emitting diode or laser diode, and a sensor, such as photodiode or phototransistor, to the exterior of the sensing volume. A symmetrical sensin g volume results which can be coupled to symmetrical input/output ports via a generally U-shaped flow path. A two part sensing chamber housing is formed with a lower cylindrical base portion and an upper cylindrical cover portion whic h slideably engage one another. At least the upper cylindrical portion carries a plurality of grooves for suppression of reflections and collection of dust. An exterior end of the upper portion carries a plurality of spaced apart openin gs which can be filled with a screen. A reduced sensing volume in combination with a selected screen size produces an acceptable signal to noise ratio and respon se rate while still excluding insects and other non-smoke related particulate matter .