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EPA Protocol Calibration T400 Ozone Analyzer Operator’s Manual
214
When F
d
has been adjusted and R has been calculated, assay the diluted concentration
with the photometer and then compare the diluted assay (A
2
) with the original undiluted
assay (A
1
) by calculating the percentage of linearity error (E) according to the following
equation.
Equation 10-2
100
A
)R/A(A
E
1
21
×=
This linearity error must be <5% in magnitude and should be <3% for a well-performing
system.
Note The result is not the true linearity error because it includes possible
instrument errors in the flow measurements. This test technique should
only be used as an indicator.
If the linearity error is >5% or is greater than you expect it to be, check and verify the
accuracy of the flow dilution carefully before assuming that the photometer is
inaccurate. The test should be carried out several times at various dilution ratios, and an
averaging technique should be used to determine the final result.
If the linearity error is excessive and cannot be attributed to flow measurement
inaccuracy, check the photometer system for:
Dirty or contaminated cell, lines or manifold.
Inadequate "conditioning" of the system.
Leaking of two-way valve or other system components.
Contaminated zero-air.
Non-linear detectors in the photometer.
Faulty electronics in the photometer.
06870C DCN6332