A method includes providing radio frequency (RF) power from an RF power supply to a showerhead of a plasma processing system running a process operation on a substrate disposed in the plasma processing system. The method senses a voltage the showerhead using a voltage probe that is connected in-line between the RF power supply and the showerhead. The sensing of the voltage produces voltage values during the running of the process operation. The method includes comparing the voltage values against a voltage check band that is predefined for the process operation being run. The comparing is configured to detect when the voltage values are outside of the voltage check band. The method generates an alert when the comparing detects that the voltage values are outside of the voltage check band. The alert identifies a type of fault based on the voltage check band that was predefined for the process operation.