Ricoh FT5034 Service Manual page 65

[Timing chart]
3. ID Sensor Output
Vsg is the ID sensor output corresponding to the drum surface erased by the erase
lamp prior to the ID sensor pattern. Vsg is almost constant.
Vsp is the ID sensor output corresponding to the sensor pattern image.
Vsp represents the toner density of the developer because it indicates the reflected
light intensity from the sensor pattern. The pattern is developed by using the present
developer in the machine.
The toner density will be controlled by comparing Vsp with Vsg.
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The bias voltage for the sensor pattern is set to 470 volts (constant) to prevent
the developed pattern density from varying according to the manual image
density level.
ID sensor output
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Main Board
ID sensor LED