Citizen CL-E720DT Technical Manual page 21

Detecting labels: (Media Sensor menu: "See Through")
For detecting label, both reflective sensor and transparent sensor are used. Label paper passes
between both sensors. The light emitted from the LEDs of the reflective sensor passes through the
liner (base part of label paper) where no label is stuck on it, and the light reaches the transparent
sensor. Accordingly, the phototransistor of the transparent sensor conducts. Meanwhile, in the
label part, the light is blocked by the label and does not reach the phototransistor. So, the
phototransistor turns OFF. By sensing the output from the transparent sensor, the CPU on the "SA
Main PCB" can detect the arrival of the label leading edge for printing.
Detecting U-shaped notches of tag: (Media Sensor menu: "See Through")
For detecting U-shaped notches of tag, both reflective sensor and transparent sensor are used.
The U-shaped notches are detected in the same way as the label mentioned above, except that
the light is directly falls on the transparent sensor through the notch.
Detecting black marks on tag: (Media Sensor menu: "Reflect")
For detecting black marks on tag, only the reflective sensor is used. Light emitted from the LEDs is
reflected by the tag (at other than the black mark) and reaches the phototransistor of the reflective
sensor. At the black mark, the light is not reflected. The CPU on the "SA Main PCB" detects the
black mark by sensing the output from the reflective sensor.
Media
Sensor to be
used
Media Sensor
menu
Label
Label
Label gap
Liner
Transparent and Reflective sensors
Transparent sensor
Media
Reflective sensor
See Trough
Tag
U-shaped
notch
LEDs
2-7
Chapter 2 Operating Principles
2-1.
Operation of Each Mechanism
Black mark
Reflective sensor
Media
LEDs
Reflective sensor
Reflect
CL-E720DT