The zero-order hold in time domain identification: An unnecessary operating premise

It is contended that transfer of identified discrete time (DT) models to continuous time (CT) on the basis that inputs that generated the measured output are constant within the inter-sample (the zero-order hold, ZOH) is unnecessarily crude when the actual inputs are band-limited signals. It is shown that the ZOH premise leads, primarily, to error in the phase angles of the entries of the modal residues. This error, as one anticipates, increases with modal to sampling frequency ratio and is important even at significant oversampling rates. Formulas to perform the transfer from DT to CT derived on the premise that the inputs are a train of Dirac impulses are shown to provide notable improvement, over the ZOH, in the accuracy of the synthesized CT model. Copyright © 2010 John Wiley & Sons, Ltd.