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GPT Theory
The principle of GPT is based on the rapid gas phase reaction between NO and O
produces quantities of NO
It has been empirically determined that under controlled circumstances the NO-O
is very efficient (<1% residual O
mixing of NO and O
conditions are met:
•
•
•
•
Given the above conditions, the amount of NO
(at a 1:1 ratio) to the amount of O
Since the O
SLPM) and the GPT chamber's volume is known, once the TOTAL GAS FLOW
requirements, the source concentration of NO, and the target concentration for the O
generator are entered into the calibrator's software. The T750 adjusts the NO flow rate and
diluent (zero air) flow rate to create the appropriate NO
Choosing an Input Concentration for the NO
It is important to ensure that there is enough NO in the GPT chamber to use up all of the
O
. Excess O
3
by most NO
The EPA requires that the NO content of a GPT mixture be at least 10% higher than the O
content. Since there is no negative effect of too much NO in the GPT chamber, API
recommends an NO concentration value higher (as much as twice as high as the highest
intended target NO
three of the four conditions listed in Section 4.2.3.1 above are therefore constant and the
NO
output can be easily and reliably varied by simply changing the O
2
EXAMPLE:
•
•
90
as shown by the following equation:
2
NO
+
O
→
NO
3
), therefore the concentration of NO
3
can be precisely predicted and controlled as long as the following
3
The amount of O
used in the mixture is known.
3
The amount of NO used in the mixture is AT LEAST 10% greater than the
amount of O
in the mixture.
3
The volume of the mixing chamber is known.
The NO and O
flow rates (from which the time the two gases are in the
3
mixing chamber) are low enough to give a residence time of the reactants in
the mixing chamber of >2.75 ppm min.
added.
3
flow rate of the T750's O
3
will react with the resulting NO
3
analyzers, this will result in false low readings.
x
value) and kept constant. As long as the flow rate remains constant,
2
Calibration values of NO
2
The NO gas input concentration should be no lower than 495 ppb and can be
as high as 900 ppb.
ν
+
O
+
h
(
light
)
2
2
being output by the T750 will be equal to
2
generator is a set fixed value (typically about 0.105
3
concentration at the output.
2
to produce NO
. Since NO
2
3
from 200 ppb to 450 ppb will be needed.
, which
3
Equation 4-4
reaction
3
resulting from the
2
3
is undetectable
3
3
concentration.
3
083730750B DCN8606
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Troubleshooting
