Model 4500 Premier Dust and Opacity Monitor93C3 Physical PrinciplesC3-1 General DescriptionThe Land Instruments International Model 4500 Premier Continuous Opacity Monitoring System (COMS)measures opacity by shining a light beam through flue gases. An internal microprocessor calculatesopacity, dust density and other parameters. The instrument comprises the following parts: The Transceiverwhich contains all of the optical and electro–optic components; the Retro-Reflector containing a glass orplastic retro-refector; the Termination Box where the customer terminations are located; and the airpurge system. A data display Control Room Unit is available.The air purge system can take several forms depending upon individual site requirements. Single anddual electric blowers are available, as are compressed-air driven devices. Continuous purge air supplyis essential to prevent dust and corrosive gases from affecting the optical system. Automatic fail–safeshutters can also be fitted for temporary protection in the event of a purge air failure.The entire system is designed for continuous operation in all weather conditions, with minimalmaintenance.Control Room UnitRetro-ReflectorTermination BoxTransceiver
