me120 lab report 1_RD

me120 lab report 1_RD - Waveform Data Acquisition...

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Waveform Data Acquisition Experiment ME 120 Experimental Methods Lab Section Tuesday 5:30pm Report by: \ Laboratory Date: September 15, 2009 Report Date: October 2, 2009 Abstract

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We used LabVIEW 8.2 to create a program where it can display two output graphs. One showed a sample graph reading that consists of a change of amplitude due to a change of time. The other was a display of a voltage power spectrum where it showed a change of amplitude due to a change in frequency from the Data Acquisition board. This was done by creating a while loop that included different relationships within the LabVIEW block diagram components that gave us the option to manipulate different inputs like Number of Samples and Sample Rates. By doing this we found that making the program run 100 samples at our chosen sample rate of 1000, the power spectrum graph outputted a range that was half of the sample rating. As the frequency was increased from the Data Acquisition and surpassed the given range, it would try to readjust itself to give a more accurate reading. We found that what was being displayed before exceeding the range was a misrepresentation of what was actually going on. This representation is called aliasing where under sampling is occurring 2
Background and Objective The purpose of this lab experiment was to familiarize ourselves with different concepts and procedures in order to accurately understand how the Data Acquisition was integrated to the program. Through this integration, we also had to see how they are related to the Sample Theorem and Aliasing. To fulfill the purposes of this experiment, we found that the higher the sample rating was, the better the representation of the output graph will be produced. i Because the graphs are going to be outputting a frequency, it was discovered through the Nyquist Criterion equation Fmax<=0.5 SF, that a maximum frequency cannot be more than half of the sample frequency. When the input frequency violates that equation, aliasing occurs. What is seen on the power spectrum graph right before aliasing occurs is not a true representation of the analog frequency. ii Procedure/ Apparatus and Experimental Results In order to perform this experiment, the equipment required is a program of LabVIEW 8.2, a National Instruments Data Acquisition Board (Model number: PCI- 6024E), and a National Instruments Data Acquisition Cable (Model Number: 184749C- 02), Ribbon Cable 1m (PN R6868), and a Jumper wire that is 24 AWG and 2 inches long.

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