Ametek Land 4500 MKIII, User Manual

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Opacity and Dust Monitor
User Guide
Model 4500 MkIII
C - 2
C2 Beer-Lambert’s Law
The mathematical relationship between the light transmitted by a medium
and the quantity of pollutant present is known as the Beer-Lambert Law and
may be written;
τ
= I = e
-acL
I
where:
τ = Transmittance
I
o
= Intensity of light into the medium (see 1 below)
I = Intensity of light out of the medium (see 3 below)
a = Attenuation Coefficient
c = Concentration of Pollutant
L = Distance light beam travels through the medium (see 2 below)
1
2
3
Since opacity (Op) = 1 -
τ
, the above equation becomes:
(1 - Op) = e
-acL
or Op = 1 - e
-acL
Note that the quantity c is the amount of dust in the optical path. Optical Density
(or extinction) is defined as;
OD = -log
10
τ
= -acL/2.303
c = k x OD where k = -2.303
aL
By comparing a series of optical density measurements with gravimetric dust
measurements taken at the same time, it is possible to determine the value of k.