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Theory of Operation Teledyne API T703 Calibrator Operation Manual
170
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:
Equation 9-7
Ρ
inHgΤ
LI
I
C
o
92.29
273
1
ln
Where:
T = sample ambient temperature in degrees Kelvin
P = ambient pressure in inches of mercury
Finally, to convert the result into Parts per Billion (PPB), the following change is made:
Equation 9-8
inHg
LI
I
C
o
92.29
273
10
ln
9
In a nutshell the T703 photometer:
Measures each of the above variables: ambient temperature; ambient gas pressure; the intensity of the
UV light beam with
and without O
3
present;
Inserts know values for the length of the absorption path and the absorption coefficient, and:
Calculates the concentration of O
3
present in the sample gas.
9.6.1.2. The Measurement / Reference Cycle
In order to solve the Beer-Lambert equation it is necessary to know the intensity of the light passing through the
absorption path both when O
3
is present and when it is not. A valve called the measure/reference valve,
physically located on front-left corner of the O
3
generator assembly (see Figures 3-4 and 9-14) alternates the
gas stream flowing to the photometer between zero air (diluent gas) and the O
3
output from the O
3
generator.
This cycle takes about 6 seconds.
Table 9-3: T703 Photometer Measurement / Reference Cycle
TIME INDEX STATUS
0 sec. Measure/Reference Valve Opens to the Measure Path.
0 – 2 sec.
Wait Period. Ensures that the Absorption tube has been adequately flushed of any
previously present gasses.
2 – 3 Seconds
Analyzer measures the average UV light intensity of O
3
bearing Sample Gas (I) during
this period
.
3 sec. Measure/Reference Valve Opens to the Reference Path.
3 – 5 sec.
Wait Period. Ensures that the Absorption tube has been adequately flushed of O
3
bearing gas.
07223B DCN6378