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EPA Protocol Calibration
The checks described in this section, if carried out carefully, will provide reasonable
confidence that a photometer which has the required inherent capability is
operating properly. Checks should be carried out frequently on a new calibrator,
and a chronological record of the results should be kept. If the record of the
photometer performance shows continued adequacy and reliability, the frequency of
the checks can be reduced with no loss of confidence in the photometer. (The
record, however, may indicate the need for continued frequent verification of the
system condition.) Even where the record shows excellent stability, the checks
should still be carried out monthly as the possibility of malfunction is always
present.
A well-designed properly built photometer is a precision instrument, and once it is
operating adequately, it is likely to continue to do so for some time, particularly if
the photometer is stationary and is used intermittently under ideal laboratory
conditions. If the photometer is commercially manufactured, it should include an
operation/instruction manual. Study the manual thoroughly and follow its
recommendations carefully and completely.
8.4.1. Linearity Test
Because the required photometric measurement is a ratio, a simple linearity check
of the photometer is a good indication of accuracy. Linearity of commercially made
photometers may be demonstrated by the manufacturer. The linearity test is
conducted by first generating and assaying an ozone concentration near the upper
range limit (80% of full scale is recommended) of the measurement range in use.
Other data points can be created by adding Zero Air (F
generated concentration (F
ensure a homogeneous concentration at the Inlet to the analyzer being calibrated.
The First step of performing this linearity test is to determine the dilution ration of
the various test points according to the following formula:
F
=
o
R
+
(
F
F
)
o
d
For this test, the flow rates F
the true value. To help ensure accurate flow measurements, the two flowmeters
should be of the same general type and one should be standardized against the
other. The dilution ratio R is calculated as the flow of the original concentration (F
divided by the total flow (F
With stable, high resolutio n flowmeters and with careful technique, R should be
accurate to within ± 1%.
194
) and pass the mixture through a mixing device to
o
and F
must be accurately measured within ±2% of
o
d
+ F
).
o
d
Model 400E Ozone Analyzer
Instruction Manual
) to the flow of originally
d
P/N 04316 Rev: B
)
o
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