54
Teledyne API Model 480H O
3
Monitor User Manual
09421A DCN8343
9. PRINCIPLES OF OPERATION
The detection of ozone molecules is based on absorption of 254 nm UV light due to
an internal electronic resonance of the O3 molecule. The 480H uses an LED lamp
constructed so that a large majority of the light emitted is at the 254nm wavelength.
Light from the lamp shines down a hollow quartz tube that is alternately filled with
sample gas, then filled with gas scrubbed to remove ozone. The ratio of the intensity
of light passing through the scrubbed gas to that of the sample forms a ratio I/Io.
This ratio forms the basis for the calculation of the ozone concentration.
The Beer-Lambert equation, shown below, calculates the concentration of ozone
from the ratio of light intensities.
o
O
n
psi
L
C
Ι
Ι
×
Ρ
×
Κ
Τ
×
×
−
=
695
.
14
273
10
6
3
α
Where:
I = Intensity of light passed through the sample
I
o
= Intensity of light through sample free of ozone
α
= absorption coefficient
L = path length
3
O
C
= concentration of ozone in parts per million
T
= sample temperature in Kelvin
P
= pressure in pounds per square inch (absolute)
