A method and apparatus of providing and improving process controls when using RF power sources in medical, industrial, or scientific processes. A further improvement results in sampling RF energy in the fundamental frequency and its related harmonic frequencies. The process control employs sampling, splitting, filtering and subsequently measuring differences between the fundamental frequency amplitude and a reference frequency amplitude and furthermore measuring the difference between the fundamental frequency amplitude and each related harmonic. Data is further digitized, processed by one or more microprocessors, time stamped and sent to upstream control systems to enable process control.