A real-time system is presented to monitor impedance match characteristics of a recently manufactured etch system, where a low pressure planar plasma is provided using multipole magnetic cores. Apart from typical radio-frequency (rf) parameters, the system particularly monitors match positions or the diagnosis of plasma impedance. Sensitivities of match positions to factor variations were examined. Statistical analysis was pet-formed over transient match data to extract further diagnostic clues. Using a real-time rf sensor, meanwhile, match positions were correlated to plasma impedance. The process factors that were varied in the experiments include source power, pressure, Ar, and O-2 flow rates. A sublinear relationship was found between each position and source power with much lessened match sensitivity in Ar or O-2 flows. Phase match position demonstrated an enhanced sensitivity over impedance match position. Statistical mean analysis of transient match data enabled further detection of shifts in plasma impedance. A catastrophic mismatch fault was correctly identified, while being illustrated as an inadequacy of reflected rf power as a diagnostic variable. Revealed further with the sensor is that plasma impedance is a strong function of reactance, which was most significant in Ar or O-2 variations. As a result, monitoring match positions in conjunction with statistical transient analysis is an effective alternative to diagnosing plasma impedance.