Frequency tuning system and method for finding a global optimum

A generator comprising:

• a controllable signal generator to generate a frequency in response to a frequency control signal;
• a power amplifier to generate power at the generated frequency;
• an output line coupled to the power amplifier a sensor coupled to the power amplifier, the sensor generates an output signal indicative of an impedance presented to the power amplifier;
• a controller that is coupled to the sensor and the controllable frequency driver, the controller provides the frequency control signal to the controllable signal generator in response to the output signal indicative of the impedance presented to the power amplifier, the controller including a processor and a non-transitory, tangible computer readable storage medium encoded with processor readable instructions for adjusting the frequency control signal, the instructions including instructions to:
• setting the frequency control signal to a current best level so the frequency driver generates a current best frequency;
• determining a current best error based upon the output signal from the sensor;
• maintaining the frequency control signal at the current best level for a main-time-period;
• changing the frequency control signal to a probe level so the signal generator generates a probe frequency;
• maintaining the frequency control signal at the probe level so the signal generator maintains the probe frequency for a probe-time-period, wherein the probe-time-period is less than the main-time-period;
• setting the current best frequency to the probe frequency if the error at the probe frequency is less than the error at the current best frequency.