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Teledyne API – Model T700 Dynamic Dilution Calibrator Principles of Operation
299
Finally, to convert the result into Parts per Billion (PPB), the following change is made:
Equation 10-8
×××=
Ρ
inHg92.29
Κ273
Τ
Lα
10
I
I
lnC
o
9
o
The T700 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.
10.7.1.2. 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 Figure 3-6 and Figure 10-13) 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 10-2: T700 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 gases.
2 – 3 Seconds
Calibrator 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.
5 – 6 Seconds
Calibrator measures the average UV light intensity of Non-O
3
bearing Sample Gas (I
0
)
during this period
.
CYCLE REPEAT EVERY 6 SECONDS
06873B DCN6388