# lab10 - MEEN 260 Texas A&M University Laboratory Manual...

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MEEN 260 Laboratory Manual Texas A&M University 1 D IGITAL F ILTER D ESIGN AND I MPLEMENTATION Created Apr. 2, 2002, B. Pautler and J. Fisher Revised Nov. 11, 2004, R. Langari Last updated Dec. 11, 2007, M. Lucas Purposes of the Experiment 1. To gain experience in utilizing circuit theory to design a digital filter. 2. To demonstrate how analog and digital devices may work together. 3. To give students experience in digital filtering and programming in the LabVIEW Environment. Theory Digital Filters Digital filtering uses discrete data points sampled at regular intervals. These data points are usually sampled from an analog device such as the voltage output of an accelerometer. Most digital filtering schemes rely not only on current value of the measured variable but also on it’s past values and thus data storage is necessary. Data can be used from previously filtered data or previously unfiltered data, which leads us to the two kinds of filters we will be examining. These filters basically find the weighted average of the data. Figure 1: Diagram of a Digital Filter

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MEEN 260 Laboratory Manual Texas A&M University 2 Input Averaging Filter In the input filter, previous unfiltered values will be used in the scheme. This filter will take the form of Y k = α U k + (1- α )U k-1 Where α is the weighting on the current value of the unfiltered signal U k . Sometimes we refer to (1- α ) as β . The remainder is from the previous value of the unfiltered signal, U k-1 . Note that we can extend this idea to more complex filters such as Y k = α 0 U k + α 1 U k-1 +…+ α n U k-n Filter with Memory In the filter with memory, previously filtered values will be used to adjust the new output. This filter will take the form of Y k = α U k + (1- α )Y k-1 where α is the weighting on the current value of the unfiltered signal, U k-1 . The remainder is from the previous value of the filtered signal, Y k-1 . Once again, sometimes we refer to (1- α ) as β . Varying α will change the amount that the data is filtered. Pre-lab: A set of data points is measured from a continuous signal as given in the following table: k Uk 0 0.10 1 1.05 2 1.92 3 3.90 4 4.02 5 4.94
MEEN 260 Laboratory Manual Texas A&M University 3 Use the accompanying Excel spreadsheet to create a simple input averaging filter with α ’s of 0.25, 0.5, 0.75, and 1.0. Which value of α gives the best performance? Justify your answer. Lab Exercise:

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lab10 - MEEN 260 Texas A&M University Laboratory Manual...

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