TUV certified Dust monitor Agasthya 2013 Series Dual Pass Transmissometer Dust Monitor BI 7000 is an optical instrument designed to measure the concentration of dust or particulate matter suspended in exhaust gas passing through a duct or stack of industrial process. Dust Monitor uses the double pass transmission measurement technology. Light beam emitted from the transmitter passes across the stack to a reflector, which then return the light to the transceiver where the intensity of the received light is measured.