Teledyne API Model 200AU NOX Analyzer Instruction Manual, 02293, Rev. F 7-26 Table 7-15: 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 un-certified 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.