The DSL 300 Particulate Monitor is an optical instrument designed to measure the concentration of dust or particulate matter in an exhaust gas passing through a duct, stack or flue. The DSL-330 uses the double pass light transmission measurement technique, with a folded beam Transceiver/Reflector arrangement. A light beam emitted from the Transceiver(TRX) passes across the duct, stack or flue to a Reflector, which then returns the light to the Transceiver where the intensity of the received light is measured. Increased particulate density in the stack gas attenuates the transmitted light and causes the intensity of the received light to fall. When Calibrated against standard reference measurements, the reduction in intensity can be used to calculate the particulate concentration and present a reading in mg/m3.