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Maintenance
Sensor Photocell Zeroing
6
6-11
8. Adjusting the photocell will cause the yellow bar to reduce in width. It should be
adjusted until the yellow line is as thin as possible over the green bar.
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Figure 6-7. Adjusting the Photocell
9. Tighten the Allen screw.
10. Often, when the Allen screw is tightened, the zero will move. Review the width of
the yellow line, again loosen the Allen screw, and now offset the yellow bar the same
width that you observed it moving from tightening the Allen screw, and now offset it
in the opposite direction by this same width.
11. Again, tighten the Allen screw. Now the width of the yellow line should be
minimized.
12. Tap on the bracket with a screwdriver handle to relieve mechanical stress. Continue
to tap on the bracket until the counts stop changing.
13. If the zero moved significantly as a result from tapping the bracket, repeat this
procedure as necessary.
14. Reinstall plastic zeroing plug.
15. After the unit has become thermally stabilized, perform a normal instrument zeroing
procedure. Refer to Chapter 6, Sensor Photocell Zeroing.
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Figure 6-8. Photocell Location