Theory of Operation 2-25SensorsThe Finisher/Inverter, Duplex Unit, and paper trays contain sensors of various typesthat perform a variety of functions. One group of sensors track the progress of thepaper along the paper path and detects if a paper jam occurs. Other sensors stopprinter activity if a door is open (interlock), detect the presence and size of media inthe trays, and monitor the fusing temperature.Photo SensorsTwo 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 anobject or condition.Photo-reflective sensors have the light emitter and light receiver aligned on a singlesurface. Output of the photo-receptor is High (> +4.5 V) when light is being reflectedback and Low (< +.3 V) when it isn’t. Photo-receptive sensors consist of a LED inone arm of a U-shaped holder, and a photo-transistor in the other arm. When thesensing area is vacant, nothing is between the arms of the sensor, light falls on thephoto-receptor sending the signal High. If the light is interrupted, the photo-transistorgoes Low.HooksHookSensor Brackets7400-310
