Measurement Method; Calculating O Concentration - Teledyne T700 Operation Manual

Principles of Operation

10.7.1. MEASUREMENT METHOD

10.7.1.1. Calculating O
298
measurements made on the sample gas in the absorption tube along with data regarding
the current temperature and pressure of the gas to calculate a final O
Concentration
3
The basic principle by which photometer works is called Beer's Law (also referred to as
the Beer-Lambert equation).
absorbed by a particular gas molecule over a certain distance at a given temperature and
pressure. The mathematical relationship between these three parameters for gases at
Standard Temperature and Pressure (STP) is:
I = I e
0
Where:
I
is the intensity of the light if there was no absorption.
o
I
is the intensity with absorption.
L
is the absorption path, or the distance the light travels as it is being absorbed.
C
is the concentration of the absorbing gas. In the case of the T700, Ozone (O
α
is the absorption coefficient that tells how well O
wavelength of interest.
To solve this equation for C, the concentration of the absorbing Gas (in this case O
application of algebra is required to rearrange the equation as follows:
I
o
C = ln
I
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:
I
o
C = ln
I
Where:
T
= sample ambient temperature in degrees Kelvin
P
= ambient pressure in inches of mercury
Teledyne API – Model T700 Dynamic Dilution Calibrator
It defines the how light of a specific wavelength is
- α LC
at STP
1
×
α L
at STP
1
× ×
α L
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concentration.
3
absorbs light at the specific
3
Τ 29 . 92 inHg
×
o
Ρ
Κ
Equation 10-5
).
3
), the
3
Equation 10-6
Equation 10-7
06873B DCN6388