Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 103)

Note that the loopback program simply checks a closed-loop path for communication effectiveness. The above steps are
given to help the user troubleshoot the entire cable system, but any fiber optic cable may be attached to the link adapter
to check for damage. For example, if the orange part of the long outdoor cable is suspected, simply connect up both
ends of the orange line to the PC link adapter and run pserver loopback, link 1. Also, a crude check may be done with a
flashlight (or sunlight). If a light is shined on one end of a particular cable, a small dot of light (about the diameter of a
hair) should be seen at the other end. However, note that the long outdoor cable ‘crosses’, that is, light going in the
orange fiber will come out the orange fiber, but one orange end will be labeled ‘IN’ and the other ‘OUT’. The short
cable inside the TGA enclosure runs straight through.
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