Ricoh FT4430 Service Manual page 64

The image density sensor checks the density of the sensor pattern image
once every 10 copy cycles. The CPU receives two voltage values directly
from the sensor: the value for the bare drum (Vsg) and the value for the
sensor pattern (Vsp). These two values are then compared to determine
whether more toner should be added.
- Detect Mode B -
is added)
When the image density is too low, the CPU activates the toner supply
solenoid to add a selected amount of toner over the next 10 copy cycles.
To maintain the image density precisely and prevent image offset, toner
supply amount is changed automatically according to the value of Vsp.
If Vsp is in condition (2), toner is added according to the supply amount
selected by SP Mode # 34. If Vsp is in condition (3), toner is added according
to the supply amount selected by SP Mode # 31.
When Vsp is less than 1/20 Vsg, toner is not supplied.
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16 April '88