Land 4500 MKII Premier, Operation And Maintenance Manual

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Model 4500 Premier Dust and Opacity Monitor
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C1 Theory of Operation and Application
C1-1 General Outline
When a beam of light crosses a medium containing smoke or dust particles, some of the light is transmitted
and some is lost due to scattering. The fraction which is transmitted is called the transmittance and
the fraction which is lost is the opacity.
In the early days of emissions measurement, the opacity of the smoke leaving a stack was measured by
the Ringelmann method in which a trained observer makes a visual estimate of its appearance.
Modern methods for opacity measurement are far more sophisticated than the Ringelmann method, but
many of the specifications relate back to the way the human eye sees smoke emissions. The wavelength
response of an opacity monitor must mimic that of the human eye. An instrument must have a nearly
photopic response. The Land Model 4500 Premier uses a high-intensity green LED light source to achieve
this.