Ricoh FT8680 Service Manual page 59

31 July 1995 OPTICS
5.11 AUTO IMAGE DENSITY CONTROL
26 mm
50 mm
A171D571.img
26 mm
50 mm
166 mm
A171D501.wmf
The original background density is read through a fiber optics cable on the
exposure lamp unit. The sampled strip is at the leading edge of the original
and the size depends on the scanner speed (reproduction ratio).
The fiber optics cable conducts the light to a photodiode on the main PCB.
The photodiode then converts the density to the ADS voltage. The CPU
compares it with the standard ADS value (+3 V), which is set at the process
control data initialization by checking density of the white pattern underneath
the left exposure glass holder and adjust the development bias accordingly.
Detailed bias control is described in the development bias section.
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