correspond with specific control means for performing this function which may be located in the doctor 1 or with control means of the machine that are programmed or designed for furthermore performing this function for example the microprocessor controller or equivalent central device of the machine which controls machine operations the coils both of the reading element 21 and of the wearing element 20 can be a printed circuit or the like can correspond with commercial coils with ferrite cores or with any other conventional element according to some implementations the reading element 21 further comprises an electronic unit not depicted in the drawings capable of generating a signal with a specific frequency or with a frequency within a specific range which is fed to the coil 21 a which is magnetically coupled with the inductive element l of the wearing element 20 the electronic unit can correspond with a generator that generates a sinusoidal signal or another type of frequency wave or with an oscillator circuit for example the power supply for powering the electronic unit to generate the magnetic excitation signal can come from the general power supply of the machine for example and the electronic unit can be continuously powered throughout the operation of the machine according to some implementations the wearing element 20 comprises a substantially l shape with a first section extending parallel to an end 10 a of the blade 10 and a second section transverse to the first section the capacitive element c being arranged in the second section and the inductive element l being arranged in the first section according to some implementations the inductive element l is arranged at the end of the first section furthest from the second.