Abstract:

The paper deals with the mechanical modeling of the dynamics of force-proving instruments in the framework of Lorentz Force Eddy Current Testing (LET). An experimental setup for this kind of measurements is presented and the obtained Lorentz force signals are analyzed. The process of system identification is discussed for two different scenarios, using force profiles, computed in numerical field simulations, as known input signals. In the first case, two independent SingleInput/Single-Output models were used to describe the dominant dynamical behavior of the experimental setup at relative high velocities. In the second case, a Multi-Input/Multi-Output model with three degree of freedoms is used to model the dynamics of a modified setup with a complex Halbach structure instead of a cylindrical permanent magnet. The signal analysis and the derivation of the Multi-Input/Multi-Output transfer function are emphasized and discussed in detail. LET requires a high velocity constancy during the linear motion of the specimen. Therefore, a mechanisms and its control is discussed, which is generating such a property on the output.

Keywords: Nondestructive testing, Lorentz force eddy current testing, vibrations, multi-body systems, model parameter identification, eigenfrequency, damping, signal processing.