Campbell Scientific CR9000X Measurement and Control System - Manual (Page 283)

Section 7. Measurement Instructions
7-59
Linear Spectral Rebinning
Linear spectral rebinning combines the spectral components from a fixed
number of adjacent bins into a single component of the final spectrum. Linear
spectral rebinning is selected by setting Fref equal to zero and SBin to two or
more. The parameter SBin determines the number of bins to combine.
Let i be the bin number of the rebinned spectrum. The center frequency of
each spectral component with linear spectral rebinning is
( )
⎟
⎠
⎞
⎜
⎝
⎛ −
− × =
2
1
bin
bin
SR
c
S
S i
N
f
i f
Where i ranges from 0 for the DC component to Floor ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
×
bin
S
N
2
for the bin containing the highest frequency component. where the
( )
x Floor
is the largest integer that is not greater than x ,
SR
f is sample rate of the
original time series (parameter FSampRate), N is the length of the FFT
(parameter FFTLen), and
bin
S is the number of bins to combine (parameter
SBin).
The difference between the center frequencies of adjacent spectral components
after linear spectral rebinning is
bin
SR S
N
f
, and bandwidth of each spectral
component (except the dc component) is also
bin
SR S
N
f
. The bandwidth of the
dc component is
N
f
SR
.
As with the original FFT results, ILow and IHigh . determine which part of
the rebinned spectrum to return. To return the entire spectrum, set ILow to its
minimum value, 0, and IHigh to its maximum value. The maximum IHigh is:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
×
bin
S
N
2
floor
where the
( )
x floor is the largest integer that is not greater than x . To limit
the lower end of the spectrum, users first select a minimum frequency of
interest,
low
f , and then set ILow to
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+
×
2
1 1
round bin
SR
low
bin
S
f
f N
S
,
where
( )
x round is x rounded to the nearest integer. To limit the upper end
of the spectrum, users select a maximum frequency of interest,
high
f , and then
set