In one exemplary embodiment described herein are innovative plasma processing methods and system that utilize direct measurement of direct current (DC) field or self-bias voltage (Vdc) in a plasma processing chamber. In one embodiment, a non-plasma contact measurement using the electric field effect from Vdc is provided. The Vdc sensing method may be robust to a variety of process conditions. In one embodiment, the sensor is integrated with any focus ring material (for example, quartz or doped-undoped silicon). Robust extraction of the Vdc measurement signal may be used for process control. In one embodiment, the sensor may be integrated, at least in part, with the substrate being processed in the chamber.