Patent ID: 6931219

Claim:
An electrophotographic color printing machine for producing color images, comprising: means for recording an image on an imaging member; a first developer unit for developing said image, said first developer unit including a sump for storing a quantity of dry developer material comprised of toner of a first color and carrier material, a member for transporting developer material from said sump, said sump including a viewing window, in communication with developer material, in said sump, an optical sensor, device for measuring reflected light off developer material, a first auger for flowing developer across said viewing window; and means for generating a signal indicative of the toner concentration in said sump, said optical sensor including a light source and a light detector, said light source emitting light at a first predefine wavelength based upon said toner of said first color; and a second developer unit for developing said image, said second developer unit including a sump for storing a quantity of dry developer material comprised of toner of a second color and carrier material, a member for transporting developer material from said sump, said sump including a viewing window, in communication with developer material, in said sump, an optical sensor, device for measuring reflected light off developer material, a second auger for flowing developer across said viewing window; and means for generating a signal indicative of the toner concentration in said sump, said optical sensor including a light source and a light detector, said light source emitting light at a second predefine wavelength based upon said toner of said second color.