Ricoh C211 Service Manual page 491

8. Ink Detection
TP1
~1
D902
5
CN104-16
OUTPUT1
VR901
TP2
D904
D903
9
m
0UTPUT2
1
-12V
I
8
Main Control P.C. B.
TRIGGER2
I
I
I
I
CN901-1, ,
Y
12 THRESHOLD
I
I
9;
2
[6]=
L--
T
1C908
lNk Detecting Board
[A]
Ink is present
NO ink is present
(1) Standard Generation Pulse
I I
I
I I
(2) Detecting Pulse
(3) Output of CN902-2
(LED 102)
[A]: Doctor Roller
[B]: Detecting Pin
[C]: Ink Roller
The ink detection circuit consists of an electrode (detecting pin), to detect the electros-
tatic capacity and a multivibrator. The pulse generated by the multivibrator is different
when ink is present and when ink is not present. This pulse is compared to a standard
pulse to detect whether or not there is ink in the drum.
(1)
(2)
(3)
The standard pulse is output from OUTPUT 1. The pulse length (To) can be ad-
justed by adjusting VR901.
OUTPUT 2 is the detection pulse. The time constant is determined by C908 and the
ink. The detection pulse is triggered by the rising edge of the standard pulse.
When ink is present, the electrostatic capacity increases and the pulse length
(TI)
becomes longer. On the other hand, when ink is not present, the pulse length
(T2)
becomes shorter as the electrostatic capacity decreases.
The pulse length
(TI
or T2) is compared with the standard pulse (To).
When the time constant
(T2
= No
ink) is shorter than the standard pulse
(To),
the
output of CN902-2 goes High.
2-78
Rev. 8189