Yokogawa In-Situ Gas Analyzer TDLS200 - Manual (Page 83)

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IM 11Y01B01-01E-A 6th Edition :Feb 13, 2013-00
<6. BASIC OPERATION>
6.5.1 Large Aperture Optics Installation, Alignment & Detector Gain
The alignment of the Large Aperture Optics (or LAO) is quite similar to the alignment method of a standard
TDLS200. To prepare for the alignment you will need some form of screen at the analyzer this can be a launch
unit with a screen and keypad, a mini display, or a laptop PC connected through VNC/Ethernet. Go into “Laser
Spectra & Control” observe the “Trans. (%)”. You will need to set up the alignment by first getting both the
launch and detect sides as perpendicular to the optical plane as possible. This will allow for the initial signal to
be found more easily. Note, the oxygen analyzers tend to be easier to align than CO/CH4 analyzers due to the
optical/detection internal configurations.
Once this has been done, adjust the launch unit till a change in transmission can be seen. Do this by loosening
the nuts from the launch unit and manually point the launch unit till some transmission is observed.
Note: the change in transmission might be very small depending on the incident angle on the detect optic. It
is easy to pass over the correct launch alignment without knowing it. If a change cannot be found,
repeat with smaller adjustments in both the X-axis and Y-axis. If no transmission can be established
by movement of the launch unit, check the general alignment of the detect unit to ensure its axis is
generally aligned with the launch unit axis.
Once some transmission is observed align the detect side so that the transmission is at a maximum. To do
this, back off all four of the setscrews. With two people, one to do the adjustments and one to watch the
transmission, slowly adjust the detect alignment by loosening one direction and tightening the opposite till the
maximum transmission can be found. Place setscrews so that the alignment is secure.
With the detector aligned begin vertical adjustments of the launch unit using the studs for small, fine
adjustments to attain maximum transmission. Once maximum transmission has been found in the vertical
position, adjust the horizontal plane for maximum transmission. With maximum transmission found in the
horizontal position repeat the alignment in the vertical position for maximum transmission. Once the maximum
transmission has been found once again in the vertical direction, align the horizontal direction again to finalize
maximum transmission alignment.
With the analyzer at maximum transmission, the beam needs to be centered on the detector. Adjust the laser
vertical plane till transmission is almost lost i.e. the edge of the beam is almost missing the detector lens.
Adjust the laser in the opposite vertical plane till the transmission is almost lost once again. Take note on how
many quarter turns that it takes to get from one side of the beam to the other. Repeat back to the other side
of the beam so that the transmission is almost lost once again. Make sure that the number of quarter turns is
similar. Adjust the beam back by half the number of quarter turns needed. The beam will be centered vertically.
Repeat for the horizontal direction using quarter turns once again. This will fully center the beam on the detector.
Now the detector will need to be aligned once again. Make sure that all backing nuts and setscrews are
securely fastened.
Carefully check the detector Large Aperture Optics bevel mounting seal is not leaking at the perimeter,
this can happen if too much bias is asserted. For oxygen analyzer and combustion processes with
negative pressure, this will cause false high readings as ambient air (20.9% O2) is drawn into the optical
path via a gap at the bevel seal edge – please clamp down all bolts and adjust the large bevel flange to
ensure a gas tight seal is maintained at all times.