An ion implanter includes a platen having a clamping surface configured to support a wafer for treatment with ions, the platen also having at least one pair of electrodes under the clamping surface, a clamping power supply configured to provide an AC signal to the at least one pair of electrodes and a sensed signal representative of the AC signal, and a controller. The C-shaped contact spring is back and forth movable to keep the nut in contact with the inner sleeve so as to achieve good grounding effect. In a master transferring step, a magnetic field is applied to a master placed close to the magnetic recording medium. The emission of a signal representative of a variation in pressure to the central unit is commanded only if the comparative change in the pressure and in the measured temperature might be representative of a variation of the amount of air in the tire. The mineral is preferably selected from calcium, iron, zinc, copper, manganese, iodine, magnesium, and mixtures of these.