Apparatus and process for the non-destructive measurement of the ohmic resistance of a thin layer using eddy currents

An apparatus for non-destructive measurement of the ohmic resistance of thin layers according to the eddy current-principle, said apparatus comprising:

• a high frequency generator;
• an oscillating circuit comprising at least an inductor and a capacitor, said inductor circuit being connected to said high-frequency generator, the inductor and oscillating circuit being provided in a vicinity of said thin layers and in a roller at certain time intervals when the roller is turning;
• means for continuously causing the frequency of the high-frequency generator and the resonant frequency of the oscillating circuit to be equal;
• a cover provided on said inductor, the surface of the cover being flush with a surface of said roller;
• a carrier foil provided over the roller with the thin layer displaceably provided thereon;
• a first means for storing a signal when the inductor is not in the vicinity of the thin layers;
• and
• a second means for storing a signal when the inductor is in the vicinity of the thin layers;
• whereby said ohmic resistance of said thin layers is determined from said signals stored in said first and second means.

A non-destructive process for measuring the ohmic resistance of thin layers utilizing eddy currents, said process comprising the steps of:

• providing the oscillating circuit comprising at least an inductor and a capacitor in the vicinity of the thin layer;
• applying a high frequency signal to said oscillating circuit;
• continuously causing the frequency of the high frequency signal and a resonant frequency of the oscillating circuit to be equal;
• providing a carrier foil of which the thin layer to be measured is displaceable;
• storing a signal from the oscillating circuit when the inductor is in the vicinity of the thin layers in a first storing means;
• and
• storing a signal from the oscillating circuit when the inductor is not in the vicinity of the thin layers in a second storing means;
• whereby the ohmic resistance of the thin layer is determined from said storing signals in said first and second storing means.

An apparatus for the non-destructive measurement of the ohmic resistance of a thin layer, comprising:

• an electrically conductive thin layer (1) having an ohmic resistance and being displaceably arranged over a roller (20) so that a part of the circumferential surface of said roller (20) is in the close vicinity of said thin layer (1);
• an inductor (2) generating a magnetic field, said magnetic field penetrating into said conductive thin layer (1);
• a high frequency generator (7);
• capacitive means (4) establishing together with said inductor (2) an oscillating circuit (3), said oscillating circuit (3) being connected to said high frequency generator (7);
• means (14) for continuously causing the frequency of the high-frequency generator (7) and the resonant frequency of the oscillating circuit (3) to be equal;
• a cover (37) provided on said inductor (2), the surface of the cover being flush with a surface of said roller (20);
• first means for storing a measuring signal from said oscillating circuit (3) when the inductor (2) is in the vicinity of said thin layer (1);
• a second means for storing a zero signal from said oscillating circuit (1) when the inductor (2) is not in the vicinity of said thin layer (1);
• and
• means for determining the ohmic resistance of said thin layer (1) by evaluating said measuring signal and said zero signal.