Ricoh FT5540 Service Manual page 83

Bias For ID Sensing
In order to develop the ID sensor pattern consistently, the CPU applies a fixed base bias level
to the development roller at the beginning of the first copy after power-up, and then once
every ten copy cycles. Fixed base bias is factory set at 500 volts dc (adjusted by SP #33).
Compensation for drum cavity temperature and drum rest time is added to the fixed base bias.
The CPU applies the ID sensor fixed base bias to the development roller about 32 milliseconds
after the scanner starts forward scan. Just after the sensor pattern is developed, the CPU
changes the bias output to the level selected by the ID keys or auto ID system. The bias
output remains at this level until the scanner starts the return scan.
Toner concentration can be increased or decreased by changing the ID fixed base bias.
Higher fixed base bias will cause the sensor pattern to be developed lighter. The CPU then
senses that the toner level is low and therefore adds more toner. This results in darker copies
as toner concentration is increased.
SP #33
ID fixed base bias:
1
0
500 380
2-35
2 3
470
530
31 August 1989