Electrode Configurations
Once one has a theory of the I-V characteristic of an electrode, one can proceed to measure it and then fit the data with the theoretical curve to extract the plasma parameters. The straightforward way to do this is to sweep the voltage on a single electrode, but, for a number of reasons, configurations using multiple electrodes and/or exploring only a part of the characteristic are used in practice.
Read more about this topic: Langmuir Probe