ABB has developed a completely new way of performing measurements with eddy current technology. It is a method that makes it possible to measure, in real time and in line, dimensions and other attributes with exceptional accuracy.
The new ABB technology is based on the measurement of the voltage pulse induced in the coil when the current is suddenly interrupted. After the abrupt interruption of the constant excitation current fed to the coil, the magnetic field produced by the eddy current in the metal sheet is measured as a factor of the voltage it induces in the coil.
At the instant of the interruption, the eddy current is present only on the surface of the workpiece and has not yet penetrated deeper into the substrate.
By tracing the entire penetration sequence via the voltage induced across the coil, we can derive three unique signal values at three different times. In this way, the new measurement technique - known as Pulsed Eddy Current technology - overcomes the limitation of the traditional design. Now all three parameters can be measured: the distance, the electrical resistivity and the thickness.
The traditional eddy current technology is based on a conventional alternating current (AC) operating principle. According to this concept, the material to be measured affects the amplitude and phase change of the electromagnetic field, yielding two parameters.
But to measure dimensions, for example, the thickness of a plate, three parameters must be taken into account: (1) the distance between the coil and the work-piece, (2) the electrical resistivity, and (3) the thickness of the metal plate, strip or bar.
When eddy current technology is applied to this type of measurement, one of the parameters must be kept constant. This is merely impossible, especially in harsh environments.