An investigation into the accelerometer mounting effects on signal transmissibility in modal measurements

The purpose of this study is to define a simple model and discuss the main effects of the use of the sensors with imperfect mounting in experimental measurements. This paper presents a theoretical and experimental investigation into the effects of different mounting methods of accelerometers on signal transmissibility in modal testing. In the theoretical part, a 2-Degree-Of Freedom (2-DOF) model is used, where the first DOF accounts for the accelerometer seismic mass and Piezo-crystal and the second DOF represents the mounting interface dynamics. An experimental modal analysis is conducted on a simple steel free-free beam using impact hammer excitation. The time domain signals and Frequency Response Functions (FRFs) are measured in the cases of magnet, wax, and stud mounting. It is found that the method of mounting has a significant effect on damping rates of measured responses. Although natural frequencies undergo no important changes, the quality of measured FRFs is degraded considerably.