A. Requirement specification A requirement specification for the probe system was set up in the beginning of the probe development, a specification which should make it possible to measure on all types of typical full-scale measurement objects: The diameter should preferably be less than 20 mm and the probe should be corona free up to 2•103 V/mm. The detection level should start at 10 V/mm or better. The resolution should typically be 10 V/mm or better (i.e. less than 1 % of typical air withstand field). Regarding the accuracy, the aim was to reach the order of 5 % at a field of 500 V/mm. It was also specified that the measuring time in continuous operation should be at least 24 hours. As described below, the newly developed probe fulfills this requirement specification.