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TELEDYNE INSTRUMENTS
460L Instruction Manual Theory of Operation
05228 Rev B 51
DCN 5164 PRINTED DOCUMENTS ARE UNCONTROLLED
10. THEORY OF OPERATION
10.1. Basic O
3
Measurement Principle
10.1.1. (Beer’s Law)
The detection of ozone molecules in a gas is based on the principle that ozone is a very strong
absorber of UV light with a wavelength of 254 nm. If the distance that this light travels through
the gas is always the same, the more ozone present in a gas, the more UV light is absorbed. If
the distance the light travels through the gas, the intensity of light passing through the ozone
containing gas, as well as the intensity of the light which does not pass through the gas are all
known, the amount of ozone present can be calculated according to the following equation, called
Beer’s Law (also referred to as the Beer-Lambert equation).
I=I
O
e
-
LC
Equation 10-1
Where:
I
o
is the intensity of the light if there was no absorption.
I is the intensity with absorption.
L is the absorption path, or the distance the light travels as it is being absorbed. This
distance determines how many molecules are present in the column of gas in the
absorption cell.
C is the concentration of the absorbing gas. In the case of the Model 460L, Ozone (O
3
).
α is the absorption coefficient absorption coefficient, a number that reflects the inherent
ability of ozone to absorb 254 nm light. Most current measurements place this value at
308 cm
-1
atm
-1
at Standard Temperature and Pressure (STP). The value of this
number reflects the fact that ozone is a very efficient absorber of UV radiation which is
why stratospheric ozone protects the life forms lower in the atmosphere from the
harmful effects from solar UV radiation.