lecture 4 noise, signal/noise ratio, detection limit
Post on 20-Dec-2015
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Lecture 4
Noise, signal/noise ratio,
detection limit
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Standard analytical terminology
Value (mean, average)
Standard deviation
Relative standard deviation(RSD)
Electronics
Signal
Noise
Signal-to-noise ratio (S/N)
RSDratioNS
1_/
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A noisy set of data
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Less noisy measurements. Signal is well visible.
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Sine wave – a primitive model of a noisy experiment
Peak-to-peak noise = 3 s (approximately)
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Noises:
Thermal BRTnoise ~
temperatureresistance bandwidth
BInoise ~Shot (quantum)
current
“Flicker”frequency
noise1
~
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Environmental noise
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A simple filter
What should I do to reduce the noise?
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Removal of the amplifier noise by filtering
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Boxcar averaging
Computer can help:
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c = a + b Random numbers a and b
sc = ?22bac sss
c = a + a 22 222aaaac sssss
2
aac
22
2 aac
sss
N
aaac
...
N
ss ac
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N
ss ac
cs
cNS /
as
NcNS /
NtmeasuremenoneNStsmeasuremenNNS )_(/)_(/
This N stands for word “noise”And this isnumber ofmeasurements
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A: one measurement, S/N=4B: 100 measurements(scans), S/N= 40
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concentration
intensity
Limit of quantitation (limit of determination)
Limit of detection (detection limit)
3s/slope
10s/slope
0
Limit of linearity