Ametek Land 4500 MKIII, User Manual

Page: 77 / 128

C - 1
Model 4500 MkIII Opacity and Dust Monitor
User Guide
C
Theory of Operation and Application
C1 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 MkIII uses a high-intensity
green LED light source to achieve this.