SYSTEM FOR MEASURING AND CONTROLLING MIXTURE CONTENT

A method of detecting the ratio of component particles in a mixture wherein the quantity of one of the component particles is continually decreased, as in an electrostatic printing operation, includes the provision of a window adjacent the path of movement of the mix of component particles and contacting particles in transit therepast, illumination of the mix through the window and detection of light reflected from the mix through the window. Replenishment of the depleted component may be electrically controlled in accordance with the light reflected and optical filter provisions may be employed to limit the spectrum of the light with which the mix is illuminated where the components of the mix differ in color. Diversion of a quantity of mix to by-pass an area wherein depletion of one component occurs effects mixing in the direction of flow and cross-flow mixing effects greater consistency in the mix transverse to the direction of flow.