Canon NP6012 Service Manual page 75

2. Monitoring the Level of Toner
a. Outline
The level of toner inside the developing
assembly is monitored by the toner level
antenna and the toner level detecting circuit.
The toner level antenna is found inside
the developing assembly, and an AC bias is
applied to the developing cylinder so that the
foner level antenna and the developing cylin-
der are bonded by static electricity whose
size varies according to the level of toner.
The copier uses the changes in the size
of this static electricity to monitor the level of
toner.
Developing bias
_ Reference signal
Comparator
circuit
Toner level detection PCB
ft Toner level signal
Toner level antenna
Developing cylinder
b. Mechanism
The toner level detecting PCB receives
an AC bias equal to the AC bias applied to
the developing cylinder and an AC bias that
represents the level of toner by the toner
level antenna. The AC bias applied to the
developing cylinder is used as a reference
signal, and the AC bias from the toner level
antenna is used as the toner level signal.
The toner level detection PCB compares
these two types of signals and sends the
results of comparison to the DC controller
PCB as the toner level signal (TNMONI).
DC controller PCB }-> e
| ee
eo0°e@
ADD TONER
indication
Developing
assembly
Figure 3-314
3-30 COPYRIGHT © 1985 CANONINC. CANON NPGO{2/NPEDI2F /NPGZ12 REV.1 SEPT. 1995 PRINTED IN JAPAN (IMPRIME AU JAPON)