Sensors; Sensor Types - Xerox Phaser 7400 Service Manual

Sensors

The printer contains sensors of various types that perform a variety of functions. One
group of sensors track the progress of the paper along the paper path, and detect if a
paper jam occurs. Other sensors detect the presence of the Toner Cartridges, stop
printer activity if a door is open (interlock), detect the presence and size of media in
the trays, and monitor the fusing temperature.

Sensor Types

The types of sensors used vary with function. In general, there are four types in use:
Photo Sensors
Two types of photo sensors are used, photo-reflective and photo-receptive.
Photo-reflective sensors use light reflected back from an object to detect its presence.
Photo-receptive sensors use an actuator or the object itself to block the light path to
detect an object or condition.
Photo-reflective sensors have the light emitter and light receiver aligned on a single
surface. Output of the photo-receptor is High (> +4.5 V) when light is being reflected
back and Low (< +.3 V) when it isn't. Photo-receptive sensors consist of a LED in one
arm of a U-shaped holder, and a photo-transistor in the other arm. When the sensing
area is unobstructed, light falls on the photo-receptor sending the signal High. If the
light is interrupted, the photo-transistor goes Low. The figure below shows a typical
photo-receptive sensor with the Hooks (catches) used to secure the sensor to its
bracket.
Hooks
Hook
Sensor Bracket
s7400-310
Theory of Operation 2-15