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Applications Note 1-6:.Electrodynamic Shaker Pseudo-Random Input:In the pseudo-random shaker method of transfer function determination,the accelerometer is mounted to an electrodynamic shaker system and apseudo-random input (broad-band noise) is presented to the sensor and thesensor response to this input is recorded. The pseudo-random input is thesummation of a large number of sinusoids of arbitrary frequency, phase,and having a defined a RMS (root-mean-square) amplitude. This calibrationis performed by plotting the power spectral density of the output of thesensor as a function of frequency.Shock Machine and Hopkinson BarShort-duration transient inputs are usually made by mounting the accelerometerto a shock machine or structural Òwave-guideÓ (Hopkinson Bar)and applying inputs that approximate the unit-impulse function. The Hopkinsonbar is a freely-suspended, simple cylindrical bar that is impacted atone end where the compression wave travels through the bar to the free endwhere the wave is converted to motion of the end plane to which the accelerometeris mounted. A reference accelerometer is generally mounted tothe free end of the bar to monitor the end-plane motion. In most cases, astrain gage, affixed to the side of the bar, is used to provide a trigger signalto a digital storage oscilloscope to allow capture of the wave form. Theunit-impulse function is not easily physically approximated due to theimpossibility of generating a pulse of unit amplitude and areaCentrifuge:Static zero-hertz input calibrations are generally performed using a centrifugesystem where the accelerometer to be tested is mounted at a knownradius on the centrifuge disc and the disc is rotated at a known speed. Theknown radius and rotational speed produce a primary centripetal accelerationloading that is directly traceable and is given by:The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-27