Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 47)

4.2 Optical Alignment
The TGA100 has a simple, robust optical design that makes it easy to adjust and maintain its optical alignment. The
optical system, illustrated in
, includes the laser, a collimating lens in front of the laser, a beamsplitter to
reflect some of the laser’s energy onto the reference detector, and two focusing lenses mounted in front of the sample
and reference detectors.
Figure 4-2
Figure 4-2. TGA100 Optical Layout
Reference
detector
The TGA optical alignment does not change during normal operation, but it should be checked after transport or after
the laser dewar is moved to evacuate it or to change lasers. To check the optical alignment, compare the reference and
sample detector signals (displayed above the detector graphs in the lower left corner of the real time screen) with the
previous values. If these signals have not changed, this indicates the alignment has not shifted. It is important when
doing this comparison for the analyzer parameters to be the same, especially the detector temperatures and the laser
temperature and current.
If the optical alignment must be adjusted, perform the following steps.
1) Loosen the transport lock screw and axial lock screw at the detector end. Note that these screws should both be
tightened only for transport. They should both be loose during operation to allow the detector end to move slightly
as the length of the long sample cell changes with temperature. Figure 4-3 illustrates the alignment hardware at the
detector end. Note that this illustration shows the horizontal adjustment screw that was included with older units;
newer units use a fine-pitch horizontal adjustment screw at the dewar end which makes horizontal adjustment at
the detector end unnecessary.
2) Loosen the horizontal and vertical clamping screws at the dewar end (illustrated in Fig ). ure 4-4
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