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Theory of Operation T400 Ozone Analyzer Operator’s Manual
278
13.1.3. THE REFERENCE / MEASUREMENT CYCLE
In order to solve the Beer-Lambert equation (see Section 10.1.2) 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. The Model T400 accomplishes this be alternately sending the sample gas
directly to the absorption tube and passing it through a chemical Scrubber that removes
any O
3
present.
ABSORPTION TUBE
Figure 13-2: Reference / Measurement Gas Cycle
The Measurement / Reference Cycle consists of:
TIME INDEX STATUS
0 seconds Measure/Reference Valve Opens to the Measure Path.
0 – 2 seconds
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 seconds Measure/Reference Valve Opens to the Reference Path.
3 – 5 seconds
Wait Period. Ensures that the Absorption tube has been adequately flushed of O
3
bearing
gas.
5 – 6 seconds
Analyzer measures the average UV light intensity of Non-O
3
bearing Sample Gas (I
0
) during
this period.
CYCLE REPEAT EVERY 6 SECONDS
06870C DCN6332