1.4.3 T/H Correction
The drum charge efficiency is the ratio of the charge actually on the drum to
the charge that was applied to the drum. It varies with the temperature
around the drum charge roller. It drops off at lower temperatures, so the
lower the temperature is, the higher the charge that is required.
Also, as the drum ages, the photoconductive layer gets worn. This causes a
decrease in the drum potential after charging.
The drum charge thermistor detects the temperature (T) around the drum
charge roller. The drum charge roller voltage is changed to account for the
effects of temperature on drum charge efficiency.
The CPU also keeps track of the drum rotation time (H) that corresponds to
the wear on the drum surface. The drum charge roller voltage is increased at
set intervals.
These corrections for the drum charge roller voltage are called T/H
correction.
The T/H correction that is applied during copying differs from that applied
when making ID sensor patterns. See below for how the correction is
determined.
The T/H correction difference between the A153, A155, and A156 copiers
and the A157, A159, and A160 copiers is a result of the difference in copy
processing speed (200 mm/s for the A153, A155, and A156 copiers,
compared with 150 mm/s for the A157, A159, and A160 copiers).
Potential of new drum
Change in drum potential
with use
A156/A160/A162 2-24 STM
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