Yokogawa In-Situ Gas Analyzer TDLS200 - Manual (Page 5)

5
IM11Y01B01-12E-A
1st Edition
In a standard TruePeak TDLS200 analyzer, the laser beam exiting the launch unit is normally
collimated parallel before hitting the opposing detect unit. The collimated beam size is typically less
than 1” diameter. However, this optical layout is not appropriate for long-path applications (the
dimension of process is longer than 23’). During the initial installation, it is also not so easy to align
the laser beam so that it can hit the targeted detect unit over a long distance (small changes in the
launch unit angle are magnified over long distances). Also it is almost impossible to keep good
alignment with varying ambient and process conditions – especially during cold starts and shut-
downs (the most extreme thermal changes on the mechanical structures).
To resolve the above issues, Yokogawa Laser Analysis Division has developed diverging beam
and large aperture optics strategy. At the launch side, the output laser beam has a small diverging
angle. For example, the beam size is about 20” (~50cm) diameter at 60’ (~18m) optical distance.
The optical aperture at the detect unit is enlarged from original diameter. With these two changes,
it is much easier to do initial alignment and keep good transmission at all operating conditions. It is
however, still important to mechanically strengthen the analyzer attachment nozzles onto the
combustion unit walls.