Calculating O Concentration - Teledyne T400 User Manual

6.1.1 C
ALCULATING
The basic principle by which the analyzer works is called the Beer-Lambert Law or
Beer's Law. It defines how light of a specific wavelength is absorbed by a particular gas
molecule over a certain distance. The mathematical relationship among these three
parameters is:
Where:
I
o
I
e
L
C
α
wavelength of interest.
To solve this equation for C, the concentration of the absorbing Gas (in this case O
application of a little algebra is required to rearrange the equation as follows:
Unfortunately, both ambient temperature and pressure influence the density of the sample
gas and therefore the number of ozone molecules present in the absorption tube thus
changing the amount of light absorbed.
In order to account for this effect the following addition is made to the equation:
C =
Where:
T
P
140
O C
ONCENTRATION
3
I = I
is the intensity of the light if there was no absorption.
is the intensity with absorption.
is the mathematical constant (Euler's number)
is the absorption path, or the distance the light travels as it is being absorbed.
is the concentration of the absorbing gas (in the case of the T400, Ozone (O
is the absorption coefficient that tells how well O
( )
I
0
C =
ln
I
( ) ( )
I
1
0
X
ln
I
αL
= sample temperature in Kelvin
= sample pressure in inches of mercury
Teledyne API – Model T400 O
Lc
-α
e
o
absorbs light at the specific
3
( )
1
at STP
X
αL
(
T
29.92 inHg
X
X
P
273K
Analyzer
3
Equation 6-1
)).
3
), the
3
Equation 6-2
Equation 6-3
)
083730400A DCN8130