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ME345_Lecture_22

ME345_Lecture_22 - o as is(no filter o with a 4 th-order...

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M E 345 Spring 2008 Professor John M. Cimbala Lecture 22 03/05/2008 Today, we will : Finish reviewing the pdf module: Filters Do some example problems – filters If time, start to review the pdf module: Op-Amps Given : A voltage signal contains useful data up to about 1000 Hz. There is also some unwanted noise at frequencies greater than 3000 Hz. We want to use a low-pass filter so that the noise is attenuated by at least 95%. We plan to use a cutoff frequency of 2000 Hz so that there is minimal attenuation of the 1000 Hz component of the signal. To do : Calculate the required order of the low-pass filter. Solution :

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Example Given : Vibrations around 90 Hz with an amplitude of about 5 V are measured with a DAQ. Data are sampled at f s = 500 Hz (exceeding the Nyquist criterion). Unfortunately, there is also some electronic interference noise at 3600 Hz, with an amplitude of about 1 V. To do : Sketch the frequency spectrum that you would expect to see for two cases:

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Unformatted text preview: o as is (no filter) o with a 4 th-order low-pass anti-aliasing filter set to a cutoff frequency of 200 Hz Solution : Example Given : A voltage signal has a frequency around 100 Hz, and ranges from 5.0 to 6.0 volts. There is also some unwanted AC noise at a frequency around 5000 Hz, with an amplitude of ± 0.005 V. The digital data acquisition system is 12-bit, and has a range from -5 to 5 volts. ( a ) To do : Calculate an appropriate DC offset and gain in order to utilize the full range of the A/D system. Solution : ( b ) To do : Design a first-order filter with these requirements: Use resistors and capacitors only • Don’t attenuate the 100 Hz signal by more than 25% (after the gain). • Attenuate the 5000 Hz noise to lower than the quantizing error of the A/D system (in other words, remove it completely, since its amplitude will be reduced to the noise level of the A/D converter). Solution :...
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ME345_Lecture_22 - o as is(no filter o with a 4 th-order...

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