EFFECTS OF ANTI ALIASING FILTER IN THE MSA HP3566A ON THE RESULTS OF FRF MEASUREMENT

• Main Author: EDWARD REMBET (NIM : 23107015); Pembimbing : Dr. Ir. Zainal Abidin; Pembimbing 2 : Ir. No, MICHAEL
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/16443
• Institution: Institut Teknologi Bandung

Recently, FRF measurement of a vibration system is performed with a digital data acquisition device such as the MSA HP3566a. On this device, the effects of aliasing on the signal spectrum are suppressed using an AAF (Anti Aliasing Filter). Unfortunately, AAF can change the vibration spectrum obtained. In this theses, the effects of AAF in the MSA HP3566a on the results of FRF measurements was investigated. Before this investigation can be performed, the type and order of the AAF must be determinated first. This determination was done by exciting the AAF with a stepped sine signal. This signal was generated using a signal generator DAC NI PCI 6281. After the filter has been identified, FRF measurement without AAF and with AAF can be modeled. The model was constructed for two systems. The natural frequency of the first system was selected to be 50% of the cut-off frequency of AAF while the natural frequency of the second system was selected to be 85% of the cut-off frequency of AAF. Those models was analyzed by using the Laplace transform method for continuous time signal and z transform method for discrete time signals. The transformation function from s domain to z domain was done by using five methods of transformation which are Impulse-Invariant Transformation Method, Numerical Solution of The Differential Equation Method, Bilinear Transformation Method, Zero Order Hold Method and First Order Hold Method. After that, transfer functions of the system were determined. Once obtained, these transfer functions were then expressed as FRF Bode diagrams. The effect of AAF for the FRF measurement can be determined by comparing the FRF Bode diagram of system without AAF and these with AAF. Based on FRF measurements of the AAF, it was concluded that the AAF in MSA HP3566a is low-pass filter. That filter consist two eigth order of Butterworth filters those are connected series. Meanwhile, the comparison between the FRF Bode diagrams of system without AAF and these with AAF show that the FRF measurement is not effected by AAF.