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 at least one transducer coupled to the at least one sensing element. The transducer is configured so as to receive a signal from the sensing element and converting the signal into a second signal for input to the information processor.