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Unformatted text preview: • Signal-to-Noise Ratio o Equals mean divided by standard deviation o It becomes impossible to detect a signal when this ratio is about 2-3 • Bandwidth o The frequency interval over which a measurement is made o The absolute frequency interval is called the pass band • Sources of Noise o Chemical noise Arises from undetected variations in temperature or pressure, fluctuations in relative humidity, vibrations, changes in light intensity, and laboratory fumes o Instrumental Noise Noise comes from each component of an instrument 4 types of noise: Thermal noise • Cause by thermal agitation of electrons or other charge carriers • Disappears only at absolute zero • Can be decreased by narrowing bandwidth o However, as bandwidth is narrower, instrument is slower to respond to measurement and more time is required • Independent of frequency itself (sometimes called white noise) Shot noise • Encountered whenever electrons or other charged particles cross a junction • Found at pn interfaces, or at evacuated spaces b/n cathode and anode •...
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This note was uploaded on 10/24/2009 for the course CHEM 447 taught by Professor Staff during the Winter '08 term at University of Michigan.
- Winter '08