Toner dispensing rate adjustment using the slope of successive IRD readings

In a method of creating tri-level images on a charge retentive surface, the steps including:

• moving said charge retentive surface past a plurality of process stations including a charging station where said charge retentive surface is uniformly charged;
• forming a tri-level image on said charge retentive surface, said tri-level image comprising two images at different voltage levels and a background voltage level;
• forming test patches on said charge retentive surface;
• using, at least one developer housing structure having a relatively long mean residence time, developing said test patches with toner to form developed test patches;
• providing a toner dispensing structure with a relatively long mean residence time for replenishing toner used for developing said test patches;
• sensing the voltage levels of said developed test patches and generating signals representative of said voltage levels wherein the time interval for sensing successive test patch voltage levels is relatively short compared to said mean residence time;
• and
• processing said signals and adjusting the dispensing rate of said toner dispensing structure in a manner which compensates for the time oscillations in toner concentration attributable to the relative values of said mean residence time and said time interval.