Emerson's OPM 3000 Opacity Dust Density Monitor ratio measurement technique provides continuous automatic compensation for variations inlight source intensity to ensure prolonged instrument accuracy and stability. Since the OPM 3000 is insensitive to the absolute intensity of the light source, it is not affected by light source aging.

Emerson's Rosemount Analytical OPM 3000 stack mounted transmissometer sensor system consists of an optical transceiver mounted on one side of the stack and a retro reflector mounted on the other. The main light source is electronically modulated and projects a collimated beam of light, which is split into a reference beam and a measurement beam. The measurement beam is projected across the stack to a retro reflector, which reflects it back across the stack to the measurement detector. The output of the measurement and reference detectors are transmitted to the control room mounted monitoring unit where all output signals are analyzed.