Systems, methods and apparatus for applying a periodic voltage function are disclosed. An exemplary method comprises applying a modified periodic voltage function to an electrical node and monitoring the modified periodic voltage function over multiple cycles to monitor a relationship d ⁢ V 0 dt - I c C 1 = D to represent a status of a plasma process or the plasma processing chamber, where Ic represents a controllable ion compensation current, D is a unitless value, d ⁢ V 0 dT represents a portion of the modified periodic voltage function that includes a negative voltage ramp, and C1 is an effective capacitance including a capacitance of a substrate support.