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Model 200E Instruction Manual EPA Protocol Calibration
8.2.3. Example GPT Calculation
Following is an example calculation that can be used to determine whether an existing GPT
calibrator will meet the required conditions for a specific calibration. For this example, it is
assumed that only the volume of the reaction cell, V
RC
, and the concentration of the NO
standard, [NO]
STD
, are known. All flow settings (F
NO
, F
O
, F
T
, and F
D
) will be calculated. In
many uses, these flow settings are known and need only to be substituted in Equations 8-5
and 8-6 to verify the required conditions. Before doing any calculations, the URL and flow
demand of the analyzer being calibrated must be known. Operating parameters are
determined from the operations manual:
• Upper range limit = 0.5 ppm, and
• Flow demand = 500 cm
3
/min.
• Volume of calibrator reaction cell is determined by physical measurement: V
RC
= 180
cm
3
• The concentration of the NO standard gas to be used is determined by reference
against an NIST-SRM (Section 2.0.7, Q.A. Handbook): [NO]
STD
= 50.5 ppm
Determine the minimum total flow (F
T
) required at the output manifold using Equation 8-1:
F
T
= 500 cm
3
/min (110/100) = 550 cm
3
/min
Because low flows are difficult to control and measure, it is often advantageous to set a
higher total flow than needed. In this example, we will set F
T
to 2750 cm
3
/min.
Determine the highest NO concentration, [NO]
OUT
, required at the output manifold, using
Equation 8-2:
[NO]
OUT
= 0.5 ppm (90/100) = 0.45 ppm
Calculate the NO flow (F
NO
) required to generate the NO concentration [NO]
OUT
, using
Equation 8-3:
min /
cm
24.5
ppm 5 . 50
min /
cm
2750 ppm 45 . 0
=
F
3
3
NO
=
×
Calculate the required flow rate through ozone generator (F
O
) using Equation 8-4:
min
cm
24.5 -
min - ppm 2.75
cm
180 x /min
cm
24.5 x ppm 50.5
=
F
3
3 3
O
/
/min
cm
260 = /min
cm
24.5 -
min
/
cm
80984 =
3 3 2 6
Verify that the residence time (t
R
) in the reaction cell is <2 min using Equation 8-5:
min 63 . 0
min /
cm
5 . 24 min /
cm
260
cm
180
= t
3 3
3
R
=
+
044100102 Rev A 131