A sensor apparatus for measuring a plasma process parameter for processing a workpiece. The sensor apparatus includes a base, an information processor supported on or in the base, and at least one sensor supported on or in the base. The at least one sensor includes at least one sensing element configured for measuring an electrical property of a plasma and may include a transducer coupled to the at least one sensing element. The transducer can be configured to receive a signal from the sensing element and convert the signal into a second signal for input to the information processor.