Patent ID: 8301049

Claim:
A method of operating an electrophotographic image forming device, comprising: providing a housing; associating a power supply with said housing; associating a control circuit including memory with said housing; associating an emitter and an associated detector with said housing; operatively coupling said emitter and said detector to said power supply and said control circuit; thereafter, while said emitter and detector are operatively connected to said power supply, emitting light from said emitter onto a first reference sample having a predetermined first reflectivity, measuring the light reflected therefrom with said detector, and producing a first signal corresponding to said light reflected from said first reference sample; adjusting a duty cycle of a pulse width modulation control signal so as to cause said first signal to substantially match a first predetermined target; storing said adjusted duty cycle in said memory as a first characterization value, said first characterization value comprising a first duty cycle value corresponding to said adjusted duty cycle used to amplify said first signal to substantially match said first predetermined target; thereafter, generating a first toner patch inside said housing and measuring a reflectance of said first toner patch with said emitter and detector based on said first characterization value while said emitter and detector are operatively connected to said power supply, and adjusting at least one electrophotographic image forming parameter based thereon; and prior to said generating a first toner patch, removing said first reference sample, emitting light from said emitter with no reference sample for said light to reflect on, measuring a signal output of said detector while driving said detector according to said first characterization value, and determining an offset value corresponding to a difference between said signal output and the first signal as amplified by said adjusted duty cycle; and wherein said adjusting at least one electrophotographic image forming parameter comprises adjusting said at least one electrophotographic image forming parameter based on said offset value.