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EPA Protocol Calibration Teledyne API – T101 Operation Manual
192
Table 7-4. Definition of Level 1 and Level 2 Zero and Span Checks
(from Section 2.0.9 of Q.A. Handbook for Air Pollution Measurement Systems)
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.
07266B DCN6485