3. NOISE:
• Noise is a collective term for sources of
unwanted signal.
Noise is defined by IUPAC as:
“the random fluctuations occurring in a signal
that are inherent in the combination of
instrument and method.”
• DEPENDENCE:
The different types of noise can be wavelength
dependent or not. They can be due to the
electronics and not dependent on the signal at
all.
4. DISADVANTAGES:
• Some noise sources introduce
systematic error, and can be corrected
for, such as with a dark spectrum.
• Other noise sources introduce random
error, and can be averaged out over
several acquisitions.
5. SIGNAL
AVERAGING:
• Signal averaging is a signal processing
technique applied in the time domain,
intended to increase the strength of
a signal relative to noise that is
obscuring it.
6. BEAM
CHOPPING:
• Beam choy pping moves the analytical
signal from zero frequency to the
frequency of the chopper.
7. TYPES:
The relevant types of noise in spectroscopy
are:
• Eletronic noise
• Line noise
• Dark current noise
• Thermal noise
• Shot noise
8. DRIFT OR 1/f
NOISE:
• 1/f noise scales with 1/frequency.
• OTHER NAME:
“Electronic noise”
• DEFINITION:
• Thus it is highest at zero frequency and
decreases as frequency increases.
9. HOW TO CONTROL
DRIFT NOISE:
• Drift can be corrected by periodically
measuring a standard and correcting for
any observed change in signal.
• This noise can be minimized by chopping.
10. LINE NOISE OR
INTERFERENCE:
• A peak at 60 Hz is likely due to
interference from the 60 Hz
transmission frequency of AC
electricity (in the US)
• Interference may occur from
other sources, such as movement
of people and equipment through
a building.
11. HOW TO CONTROL LINE
NOISE:
• Electrical shielding
• Ground shielding
• Instrument to the same ground
• Physical isolating the instrument
Can help reduce interference.
This noise can be minimized by chopping.
13. GENERATION:
This type of noise is also thermally generated,
but instead of current fluctuations due to the
random motion of charge carries, dark current
noise is created by
“thermionic emission of electrons from
photocathode.”
14. HOW TO CONTROL DARK
CURRNET:
Can be significantly reduced by;
“cooling the system.”
15. WHITE NOISE OR GUASSIAN NOISE:
OTHER NAME:
“Johnson-Nyquist noise.”
Or
“Thermal noise”
DEFINITION:
electrical fluctuations arising
from the random
thermal motion of
electrons
16. GENERATION:
• One source of white noise arises from random fluctuations of electrons in
an electric device.
• This thermal noise actually occurs regardless of the applied voltage
because the charge carriers vibrate as a result of the temperature.
17. HOW TO CONTRL THERMAL
NOISE:
• Naturally we can reduce Johnson noise by reducing the temperature of
the device.
18. SHOT NOISE:
“Shot noise arises from the quantized nature of charge carries and photon”
OTHER NAME:
“Poisson noise”
19. GENERATION:
• If the signal is very low, then random variation in the small number of
incoming photons or generated electrons and holes (in a semiconductor )
causes noise.
• The shot noise in the semiconductor radiation detector is due to the
discrete flow of carrier in the device.
