LumaSense Technologies 3434i SF6 Leak Detector - Manual (Page 160)

Chapter 12
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BE6028-14 3434i SF6 Leak Detector LumaSense Technologies A/S
Page 160 of 191
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.12.13).
Fig.12.13 Curve showing a linear span-calibration curve
Choosing a filter bank
If a filter (e.g. “A”) has already been calibrated to measure a gas
(e.g. A1) and you wish to calibrate with gas A1 again, then select the
filter bank containing the gas conversion factor for gas A1. Online
users can do this when downloading the calibration factors. Stand-
alone users should do this before setting-up and performing the span
calibration task. The gas conversion factor calculated during the
span calibration will then just overwrite the gas conversion factor
calculated during the previous span calibration of the filter with this
gas.
If you wish to span calibrate a filter to measure more than one gas,
then select a new filter bank each time you span calibrate with a