DESIGN, THEORY AND VALIDATION OF A LOW MASS 6-d.o.f. TRANSDUCER

The need for measuring multidirectional responses is becoming increasingly important in applications such as modal analysis, verification of dynamic models, etc. Therefore, a transducer comprised of a fixture containing six linear accelerometers has been developed and tested in order to measure six degrees of freedom at a point. The term transducer in this context includes both the fixture and the six accelerometers. In order to minimize the loading of the measurement object, the weight of the transducer is kept small by using low weight accelerometers and a hollow aluminum fixture. At the same time, the transducer is designed sufficiently stiff in order to consider it as a rigid body for use up to approximately 600 Hz. For the motion of the transducer, systems of equations are derived which include the transverse sensitivities of the six accelerometers. The influence of the transverse sensitivity is investigated in a parameter study on a structure consisting of a three-dimensional beam structure, excited in such a way that motion results in all directions. The transducer design leads to two important measurement features; a centrally located hole in order to measure and excite driving point frequency response functions and a flat surface in order to measure close to the surface of the structure. Experimental results are compared with theoretical ones. It was found that the major limitation of the transducer results from the inherent transverse sensitivities of the accelerometers.