Canon 1000 Service Manual page 158

3. OPERATION AND TIMING
e. Measuring the Toner by the SALT Sensor
To check the density of toner within the developer, a toner image is formed on the photosensitive drum
after copying operation. This measurement of density is done by the SALT sensor (Figure 3-542) mounted to
the side of the photosensitive drum. A density pattern is formed on the photosensitive drum, and infrared light
is shone against the density pattern to measure the density with reference to the reflected light.
DC controller
Direct intensity/re-
flected intensity
Bk
SALT sensor
The changes in the LED intensity over time or
caused by changes in ambient temperature are
corrected in the same way as for color toner. Since
the window of the sensor tends to become soiled
with stray toner, correction is made for the dirt on
the window also.
The LED is turned on during last rotation after
copying operation, and the light reflected by the
surface of the photosensitive drum without a
deposit of toner is read. The difference between
the measured value and the initial value is used as
a correction value when computing the density of
the density pattern.
3-114
COPYRIGHT © 2001 CANON INC.
Toner supply signal
Color toner
density sensor
C
SALT sensor
SALT sensor
Transfer belt
Figure 3-542
Direct intensity signal
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
CL
Toner supply clutch
Color toner
density sensor
Y
M
SALT sensor
Detection of direct light
LED
Mirror
Reflected intensity signal
Figure 3-543
Color toner
density sensor
Photosensitive drum
Detection of reflected light