TRANSDUCER INERTIA AND STINGER STIFFNESS EFFECTS ON FRF MEASUREMENTS

In order to study methods for measuring complete driving point frequency response function (FRF) characteristics for forces and moments, it was necessary to evaluate which test technique had the best chances of success. Impulse testing has consistency problems with input magnitudes and direction as well as mixing windows for signal processing. The chirp has excellent signal-tonoise ratios and generally superior coherence when compared to both random and impulse testing. It was found that stinger resonances within the test frequency range and later outside the test frequency range caused measurement complications for certain test structure natural frequencies. These complications were effectively predicted using the transducerʹs inertial properties, the stingerʹs stiffness properties, and the structureʹs linear and angular driving point FRF characteristics (as determined from impulse tests) when stinger resonance effects were removed from the chirp data.