HP 2500C Series - Manual (Page 135)

Functional Overview 6-15
Paper Paths and Components
Output stack sensing is based on fixed field proximity sensing using two LEDs side by
side.These LEDs have both light source emitters as well as receivers. In short, it is based
on the concept of fixed distance sensing and ignoring any objects that lie beyond their
sensing range regardless of object surface reflectivity e.g. plain paper vs. glossy paper.
(But Transparencies will affect the sensing distance, they are detected earlier by 8mm)
Sensor is mounted on the carriage wall directly on top of the BOF of media (which is
approx. 10mm). As BOF is the non-printed area, this is used as the reflecting surface for
the light so that the variation in colour/text content of the output media does not have any
influence. Fixed field sensors compare the amount of reflected light that is seen by two
differently aimed receiver optical elements. A target is recognised as long as the amount
of light reaching receiver seen by one receiver is greater than other.
Distance of sensing( from the bottom of the sensor to paper full level) = 35mm