Patent ID: 6928250

Claim:
An electrophotographic printing machine of the type having a latent image recorded on an imaging member wherein said latent image is developed and transferred to a media substrate during successive printing cycles of successive print jobs, comprising: a charging device for producing a voltage potential on the media substrate to transfer the developed latent image to the media substrate, said charging device including a coronode member and shield; a first voltage supply for apply a shield voltage to said shield; a second voltage supply for applying a wire voltage to said coronode member; a voltage monitor for measuring the voltage on the shield, said voltage monitor periodically polling the voltage during a cycle of a print job and generating a voltage measured signal as a function thereof; control means, responsive to a media type of each media substrate and said voltage monitor, for adjusting said wire voltage to said coronode member in respect to said shield voltage to said shield to compensate for process impedance as said media substrate passes under said charging device to obtained desirable image transfer.