Chapter 5 (1) - Chapter 5 Signals and Noise Signal carries...

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Chapter 5 Signals and Noise Signal carries information about the analyte that is of interest to us. Noise is made up of extraneous information that is unwanted because it degrades the accuracy and precision of an analysis Signal-to-Noise Ratio S/N = (mean)/(Standard deviation) = Signal-to-noise (S/N) is much more useful figure of merit than noise alone for describing the quality of an analytical method. The magnitude of the noise is defined as the standard deviation s of numerous measurements and signal is given by the mean x of the measurements. S/N is the reciprocal of the relative standard deviation. S/ N < 2 or 3 impossible to detect a signal. x s R S D = 1
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Figure 5-1 Figure 5-2
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Sources of Noise Analysis are affected by two types of noise: 1. Chemical noise 2. Instrumental noise Chemical noise: Arises from an uncontrollable variables that effect the chemistry of the system being analyzed. Examples are undetected variations in temperature, pressure, chemical equilibria, humidity, light intensity etc.
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Instrumental Noise: Noise is associated with each component of an instrument – i.e., with the source, the input transducer, signal processing elements and output transducer. Noise is a complex composite that usually cannot be fully characterized. Certain kinds of instrumental noise are recognizable, such as: 1. Thermal or Johnson noise 2. Shot noise 3. Flicker or 1/f noise 4. Environmental noise
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Instrumental Noise 1. Thermal Noise or Johnson Noise: Thermal noise is caused by the thermal agitation of electrons or other charge carriers in resistors, capacitors, radiation transducers, electrochemical cells and other resistive elements in an instruments. The magnitude of thermal noise is given by where, ν rms = root mean square noise, f = frequency band width (Hz), k = Boltzmann constant (1.38 x 10 -23 J/K), T = temperature in Kelvin, R = resistance in ohms of the resistive element. Thermal
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Chapter 5 (1) - Chapter 5 Signals and Noise Signal carries...

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