The general concept of developer “conductivity” is known to play a role in development rate and efficiency, but a packed powder cell measures conductivity under conditions quite different from an actual toning nip. For a two-component developer with magnetized carrier, the developer is magnetically agitated as it flows through the toning zone, while in the packed cell it is static. A test cell was constructed which agitates a thin layer of developer and subjects it to brief voltage pulses, as it would realistically experience in a nip transition. In many cases of interest the developer is insulating enough that most of the current is capacitive, making actual toning current difficult to discern. This particular problem can be overcome by designing the measurement circuit as a compensated probe, that is, with a capacitor in parallel with the current sense resistor. Example waveforms give evidence of a nonlinear conduction process in toning.
Graham S. Wright, "Conductivity and Time-Constant Measurements on Magnetically-Agitated Electrophotographic Developer Using the Method of the Compensated Probe" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP19), 2003, pp 22 - 27, https://doi.org/10.2352/ISSN.2169-4451.2003.19.1.art00008_1