LumaSense Technologies INNOVA 1314i - Manual (Page 133)

Chapter 12
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BE6030-13 1314i Photoacoustic Gas Monitor LumaSense Technologies A/S
Page 133 of 199
12.1 About the Installed Optical Filters
In collaboration with LumaSense Sales Engineers, you have chosen
the optical filters that are best suited to your measuring task. Each of
these optical filters has been installed in one of the positions marked
“A”, “B”, “C”, “D” or “E” of the filter carousel wheel in your Monitor. A
special optical filter, which is selective to water vapour, is always
installed in position “W”.
Each optical filter has to be span calibrated with the gas it is to
measure. If this span calibration is not performed the Monitor is
unable to measure accurately.
Each filter in the carousel has to be fully calibrated before the
Monitor can perform accurate gas measurements. The practical
calibration procedure is fairly simple; it involves performing
measurements with the Monitor while various gas supplies are at-
tached to its air-inlet.
A full calibration of the water-vapour filter SB 0527 involves:
· Zero-point calibration (using a zero-gas * )
· Span calibration (using a known concentration of water vapour)
A full calibration of the optical filters in position “A” to “E” involves:
· Zero-point calibration (using a zero-gas*)
· Humidity-interference calibration (using water-vapour)
· Span calibration (using a known concentration of the gas this
filter is to measure)
· Cross-interference calibration (when this is necessary). If the
gas to be measured by filter “A” actually absorbs light from any of
the other installed optical filters it will interfere with the signal
measured when the other optical filters are used. If this is the
case, it is necessary to perform a cross-compensation calibration
of this filter. This involves taking measurements with all the other
installed optical filters while the span calibration is performed.
The following sections explain what a calibration is and why it is
necessary. Some of the expressions used in this chapter are also
explained, to help you understand the process.
* A zero-gas is a gas which does not absorb infra-red light e.g. pure Nitrogen.