Method and apparatus for detecting and correcting the positions of electrodes, in particular in shock wave generator apparatus using a feeler finger, e.g. the rod of an actuator, movable to the focus

In a method of detecting and correcting the positions of electrodes to a predetermined distance d symmetrically about a specified point in three dimensions at which an electric arc is to be generated between the electrodes, said point being referred to as the focus, said method comprising the following steps:

• (a) providing detector means capable of detecting the presence of an electrode and disposing said detector means at a predetermined point in three dimensions, referred to as the "detection" point, said detection point being situated on the path of electrode displacement, said detector means being suitable for detecting the presence of an electrode at said detection point;
• (b) advancing one of the electrodes until said one electrode comes into contact with said detector means disposed at said detection point;
• (c) detecting the presence of the electrode at said detection point;
• (d) retracting said one electrode so as to position it at said predetermined distance d therefrom;
• (e) repeating steps (b)-(d) for each other electrode;
• and
• (f) retracting said detector means from said detection point;
• thereby enabling the position of the electrodes to be corrected regardless of the number of discharges for which the electrodes have been used.