determining whether a current increase or decrease has been detected the change in value must exceed a current window that is given either as input to the system or determined by the system the system for example determines the appropriate current window that is required on a periodic basis by taking a series of measurements at the same bias level and determining standard deviations or uncertainty levels by standard statistical algorithms an acceptable change in current is then determined by requiring an absolute change in current values greater than a value representative of a given certainty level or multiple of the standard deviation 4 if the current is already at a maximum a periodic check on this condition is performed by successively decreasing voltage bias 18 in a stepped manner until two or more successive decreases in current levels are detected voltage bias 18 is then stepped in increasing increments until two or more successive measurements with the same current value are detected the cycle is repeated with smaller voltage steps one or more times processor 38 determines a maximum current and sets an optimal voltage bias e g the minimum bias necessary to achieve a selected percentage of maximum current it will be appreciated that processor 38 may construct a learned database i e operating conditions associated with key parameters such as optimal bias settings current values appropriate voltage steps and current windows such a stored database would be used as a starting point for system operation but would be updated on a periodic basis to verify optimal conditions other system operating variables are optimized using the basic procedures discussed above for example if the system is operating under reduction limited conditions an increase.