Canon NP6621 Service Manual page 107

2. Toner Level Detection Control
The level of toner inside the cartridge is monitored
by the antenna sensor circuit.
Inside the cartridge is the toner level sensor, and
an AC bias is applied to the developing cylinder.
The developing cylinder and the toner level
sensor are bonded statistically, and the amount of
static charge between the two varies according to
the level of toner inside the cartridge. For this
reason, an AC bias which suits the level of toner is
Blade mount
Toner
Blade
Developing cylinder
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Toner level
Developing assembly
sensor
frame
Figure 3-313
CANON NP6621 REV.0 FEB. 1998 PRINTED IN JAPAN (IMPRIME AU JAPON)
OPERATIONS AND TIMING
identified by the toner level sensor and communi-
cated to the antenna sensor circuit.
The antenna sensor circuit is directly supplied
with a specific, attenuated AC bias by the composite
power supply for use as a reference signal.
The antenna sensor circuit compares the signal
from the toner level sensor against the reference
signal to find out the level of toner.
Antenna sensor circuit
Comparator circuit
DC controller
PCB
TEP*
3–51