bmen_305_lab_4

bmen_305_lab_4 - Introduction The purpose of this lab was...

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Introduction: The purpose of this lab was to introduce op-amps and active filter circuits to the student. The lab demonstrates how op-amps and active filter circuits can be used to amplify or remove frequency components from a signal. Spectral analysis of signals via Fast Fourier Transform (FFT) graphs and Bode plots was also learned. Materials and Methods: 741 op-amp 1.6k, 800, 500k, 2 18k, 1M, 160k, 22.5k, 12k, 2 45k Ohm resistors 1 μ, 2 50n, 100n, 2 1.5 n Farad capacitors Procedure: Part 1: ECG Restoration The circuit shown in Circuit Diagram 1 was constructed. Using the function generator on the table, a sawtooth signal was generated for the input of the circuit. The output signal was acquired on the NI ELVIS software. Figure 1: Circuit Diagram used for sawtooth analysis. Next, a capacitor was added, creating the circuit shown in Circuit Diagram 2. The frequency of the input signal was slowly increased, and the output change was observed on the graph. 1
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Figure 2: Circuit Diagram of Low pass filter, used with increasing frequency Then, the input and outputs of the circuit were disconnected. FUNC_OUT was wired to both Vin and ACH1+. Vout was wired to ACH0+. ACH0- and ACH1- were grounded. NI ELVIS’ Bode Analyzer was opened. The start frequency was set at 1 Hz, and the stop frequency was set at 1000 Hz. The analyzer was started and the Bode plot was obtained. Finally, a realistic experiment was done. It was supposed that an ECG signal was acquired with a large amount of noise affecting the heart rate monitor software. The problem was determined to be high-frequency interface. The simplest solution is a low-pass filter. The input on the circuit was moved from FUNC_OUT to DAC0. The VI provided, shown below as VI 1, was run. 2
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Figure 3: VI 1 ECG signal creator Part II: Convoluted Sines For this part of the lab, a second order 150 Hz high-pass filter was built to look like the figure given. It was assumed that a 200 Hz sine wave with 2V amplitude was receiving interference from an unknown source. Using the same method as in part one, a Bode plot of the filter was constructed. Then, using LabVIEW, and clicking on the Part II tab, the vi provided for us was opened and run. The input of the circuit had to be moved from FUNC_OUT to DAC0 to use the Bode Analyzer. Next, a second order 250 Hz low-
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This note was uploaded on 11/03/2009 for the course BMEN 305 taught by Professor Meissner during the Spring '07 term at Texas A&M.

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bmen_305_lab_4 - Introduction The purpose of this lab was...

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