Sensors - Xerox Paser 7400 Service Manual

Sensors

The Finisher/Inverter, Duplex Unit, and paper trays contain 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 detects if a paper jam occurs. Other sensors stop
printer activity if a door is open (interlock), detect the presence and size of media in
the trays, and monitor the fusing temperature.
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 vacant, nothing is between the arms of the sensor, light falls on the
photo-receptor sending the signal High. If the light is interrupted, the photo-transistor
goes Low.
Hooks
Hook
Sensor Bracket
s7400-310
Theory of Operation 2-25