Patent ID: 8380091

Claim:
A method of measuring developer density in an electrophotographic system, comprising: providing a first electrode and a second electrode disposed to define a working volume between them through which developer passes without contacting the first electrode, wherein the electrodes are electrically insulated from each other by the working volume; connecting one terminal of a voltage source for selectively providing an AC bias having a selected frequency to one of the electrodes; providing an inductor in series with the voltage source, the inductor being connected to the other of the electrodes, whereby the source provides the AC bias across the electrodes through the inductor; applying the bias using the voltage source; measuring the current across the electrodes while the bias is applied; repeating the applying and measuring steps so that multiple biases having different frequencies are applied and respective currents are measured; and automatically determining the density of the developer in the working volume using a processor based on the multiple biases and the measured respective currents.