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Model 9110T NOx Analyzer EPA Protocol Calibration
Teledyne Analytical Instruments 224
Any repairs which might affect its calibration.
Physical relocation of the analyzer.
Any other indication (including excessive zero or span drift) of possible significant inaccuracy of the
analyzer.
Following any of the activities listed above, the zero and span should be checked to determine if a
calibration is necessary. If the analyzer zero and span drifts exceed the calibration limits in Section 12 of
the Q.A. Handbook
6
, a calibration should be performed.
10.4. LEVEL 1 CALIBRATIONS VERSUS LEVEL 2 CHECKS
All monitoring instruments are subject to some drift and variation in internal parameters and cannot be
expected to maintain accurate calibration over long periods of time the EPA requires a schedule of
periodic checks of the analyzer’s calibration be implemented. Zero and span checks must be used to
document that the data remains within required limits. These checks are also used in data reduction and
system validation.
A Level 1 Span check is used to document that the 9110T is within control limits and must be conducted
every 2 weeks. A Level 2 Span Check is to be conducted between the Level 1 Checks on a schedule to
be determined by the user.
Table 10-2: Definition of Level 1 and Level 2 Zero and Span Checks
LEVEL 1 ZERO AND SPAN CALIBRATION
A Level 1 zero and span calibration is a simplified,
two-point analyzer calibration used when analyzer
linearity does not need to be checked or verified.
(Sometimes when no adjustments are made to the
analyzer, the Level 1 calibration may be called a
zero/span check, in which case it must not be
confused with a Level 2 zero/span check.) Since
most analyzers have a reliably linear or near-
linear output response with concentration, they
can be adequately calibrated with only two
concentration standards (two-point concentration).
Furthermore, one of the standards may be zero
concentration, which is relatively easily obtained
and need not be certified. Hence, only one
certified concentration standard is needed for the
two-point (Level 1) zero and span calibration.
Although lacking the advantages of the multipoint
calibration, the two-point zero and span
calibration--because of its simplicity--can be (and
should be) carried out much more frequently.
Also, two-point calibrations are easily automated.
Frequency checks or updating of the calibration
relationship with a two-point zero and span
calibration improves the quality of the monitoring
data by helping to keep the calibration relationship
more closely matched to any changes (drifts) in
the analyzer response.
LEVEL 2 ZERO AND SPAN CHECK
A Level 2 zero and span check is an "unofficial" check of an
analyzer's response. It may include dynamic checks made with
uncertified test concentrations, artificial stimulation of the
analyzer's detector, electronic or other types of checks of a
portion of the analyzer, etc.
Level 2 zero and span checks are not to be used as a basis for
analyzer zero or span adjustments, calibration updates, or
adjustment of ambient data. They are intended as quick,
convenient checks to be used between zero and span
calibrations to check for possible analyzer malfunction or
calibration drift. Whenever a Level 2 zero or span check
indicates a possible calibration problem, a Level 1 zero and
span (or multipoint) calibration should be carried out before any
corrective action is taken.
If a Level 2 zero and span check is to be used in the quality
control program, a "reference response" for the check should be
obtained immediately following a zero and span (or multipoint)
calibration while the analyzer's calibration is accurately known.
Subsequent Level 2 check responses should then be compared
to the most recent reference response to determine if a change
in response has occurred. For automatic Level 2 zero and span
checks, the first scheduled check following the calibration
should be used for the reference response. It should be kept in
mind that any Level 2 check that involves only part of the
analyzer's system cannot provide information about the portions
of the system not checked and therefore cannot be used as a
verification of the overall analyzer calibration.
In addition, an independent precision check between 0.08 and 0.10 ppm must be carried out at least once
every two weeks. Table 10-1 summarizes the quality assurance activities for routine operations. A
discussion of each activity appears in the following sections.