Feb02_2005_2pp

# Feb02_2005_2pp - ± Two methods we’ll...

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1 February 2, 2005 ¾ Transition Week : Finish Signals and Noise and begin ELECTROCHEMISTRY ¾ Reminder: Exam #1, Feb. 16 th at 7pm! ¾ Info page will be posted early next week ¾ Email me next week if you have a conflict with the time 2 More Signal Averaging ± Signal must be digitized . . . How? ± Digitization frequency? - Nyquist Theorem ± Precision of digitization? - how many bits? 8-bit = 2 8 = 256 (0.4 %) 12-bit = 2 12 = 4096 (0.02 %) analog digital

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3 Signal Averaging a Spectrum •Get same S/N enhancement: -incr. with n 1/2 •Need good synchronization for each replicate scan 4 Boxcar Averaging ± Just a single-channel signal averager: -select a single delay time -integrate signal over selected time gate -average signal for n-replicates - repeat at new delay time ± Gives S/N incr. with n 1/2 for each data point
5 Digital Filtering ± Can manipulate digitized signals to improve S/N -can do this after data collection -don’t need a repetitive signal

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Unformatted text preview: ± Two methods we’ll consider:-Savitsky-Golay Smoothing (time domain)-Fourier Filtering (frequency domain) 6 Savitsky-Golay Smoothing ± A weighted moving average applied to a series of data. EXAMPLE: 3-point smooth 1. Select the first 3 data points 2. REPLACE the central data point with the weighted average of the first three data points 3. Select data points 2-4 and repeat 7 Fourier Filter/Smooth ± We would have greater control if we were to do this in the frequency domain: 8 Beware! ± It is easy to smooth/filter signal as well as noise-overlay original and processed waveforms-make sure that result is not distorted ± Need high point density-trade-off between resolution and noise (high point density = greater ∆ f)-trade-off between and time (lotsa data points = incr. storage and processing time)...
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## This note was uploaded on 05/15/2010 for the course CHEM 221 taught by Professor Joelgoldberg during the Spring '10 term at UVM.

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Feb02_2005_2pp - ± Two methods we’ll...

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