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TELEDYNE INSTRUMENTS
Theory of Operation 460L Instruction Manual
52 05228 Rev B
PRINTED DOCUMENTS ARE UNCONTROLLED DCN 5164
To solve this equation for C, the concentration of the absorbing gas (in this case O
3
), the
application of a little algebra is required to rearrange the equation as follows:
LI
I
C
o
1
ln
Equation 10-2
Unfortunately, both ambient temperature and pressure influence the density of the sample gas
and therefore the number of ozone molecules present in the absorption path thus changing the
amount of light absorbed.
In order to account for this effect the following addition is made to the equation:
Ρ
psi695.14
273
Τ
L
1
I
I
lnC
o
o
Equation 10-3
Where:
T = sample ambient temperature in degrees Kelvin
P = ambient pressure in pound per square inch (psi),
Finally, to convert the result into Parts per Million (PPM), the following change is made:
psi695.14
273
L
10
I
I
lnC
o
6
o
Equation 10-4
10.1.2. The Absorption Path
In the most basic terms, the Model 460L uses a high energy, mercury vapor lamp to generate a
beam of UV light. This beam passes through a window of material specifically chosen to be both
non-reactive to O
3
and transparent to UV radiation at 254nm and into an absorption tube filled
with Sample Gas.
Because ozone is a very efficient absorber of UV radiation the Absorption Path Length required to
create a measurable decrease in UV intensity is short enough (approximately 16 cm) that the light