Ricoh FT4460, Service Manual, Page: 69 / 413

23 May
1989
3.9 AUTOMATIC IMAGE DENSITY SENSING
The input for the automatic image density circuit is via a fiber optic cable [A]
mounted on the first scanner. Light from the exposure lamp [B] passes
through a small hole in the reflector, reflects from the original, and is collected
by the fiber optic cable. The sampled strip starts 18 millimeters from the lead-
ing edge of the original.
The detecting length L of the ADS circuit is determined by the following equa-
tion in each copy mode:
88 mm
Black copy mode: L =
Reproduction Ratio
44 mm
Color copy mode: L =
Reproduction Ratio
The highest voltage detected by the ADS is held (peak hold) and used for the
bias voltage adjustment. The ADS system will change the developer bias to
adjust the image density for optimum copy quality. This ADS system has
three base levels (N,D,L) to allow the system more flexibility. SP Mode #34
switches the settings as follows:
N: Normal (base levels)
D: Dark (no exposure lamp change, bias increases 40V)
L: Light (2V exposure lamp voltage increase, no bias increase)
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