LumaSense Technologies INNOVA 1314i - Manual (Page 160)

Chapter 12
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BE6030-13 1314i Photoacoustic Gas Monitor LumaSense Technologies A/S
Page 160 of 199
interference calibration cannot be performed alone! It has to be
performed together with the span calibration of each of the installed
optical filters. Cross-interference calibration is not selective, that
is, if you select to perform a cross-interference calibration, then each
time a gas is supplied to the Monitor during a span calibration, the
signal in the cell is measured using each installed optical filter. You
cannot choose which filters should be calibrated for cross-
interference from a particular gas.
Section 12.9 includes information about how to set up a combined
cross-interference and span calibration task.
12.9 Span Calibration
Before calculating the conversion factor for a filter (during span
calibration) a concentration offset factor and a humidity gain
factor must be in the filter bank which is selected for the filter
during span calibration. Span calibration of a filter can therefore only
be done after the filter has already been zero-point and humidity-
interference calibrated.
During span calibration a supply of a particular gas (e.g. gas A1) of
known concentration is attached to the air-inlet of the Monitor and
the total signal in the cell is measured using the water-vapour filter
and the filter which is being span calibrated (for example “A”). As
filter “A” has already been calibrated for humidity interference, the
total signal (V
total
) measured with filter “A” can be compensated for
any signal produced by water-vapour’s absorption of light from filter
“A” (V
H2O
) during the span calibration task. This means that your
span gas does not have to be perfectly dry. As the filter has already
been zero-point calibrated, the cell noise V
offset
(when filter “A” is
used) is known, and therefore the span calibration curve can be
drawn (see Fig.12.14 ).