Campbell Scientific CR9000X Measurement and Control System - Manual (Page 121)

Section 3. CR9000X Measurement Details
Chart 3.3-3 Frequency Response
0
0 .2
0 .4
0 .6
0 .8
1
1 .0 E - 0 4 1 .0 E -0 3 1 .0 E -0 2 1 .0 E - 0 1 1 .0 E + 0 0 1 .0 E + 0 1 1 . 0 E + 0 2 1 .0 E + 0 3 1 .0 E + 0 4 1 .0 E + 0 5
F r e q u e n c y ( L o g S c a le )
R
e
l R
esponse
T a u = 5 .0 S e c o n d s
T a u = 0 .5 S e c o n d s
T i m e C o n s t a n t
= 5 S e c o n d s
T im e C o n s t a n t
= 0 .5 S e c o n d s
The time constant used is determined by the VoltFilt's
"Excitation" parameter setting. TIP
WINDOWING
The FFT option allows radix-two (2 n , where n = 5, 6, …16) transform lengths
ranging from 32 to 65,536 samples (allowing the user to set up the
measurement to have the appropriate Bin resolution). Users can optionally
apply a Hanning, Hamming, Blackman-Harris, or one from a selection of
Kaiser-Bessel beta choices, window function to their time series before
transforming them. The beta (Kaiser-Bessel) allows the user to trade spectral
leakage for spectral resolution. Table 3.3-1 shows the maximum out of band
leakage and the full width, half of maximum (FWHM) spectral resolution
monitoring a monochromatic signal using four different betas. Chart 3.3-4
shows graphically the bin resolution (or bin smearing effect) for no
windowing, the Hanning window and 4 Kaiser-Bessel betas.
Table 3.3-1. Spectral Leakage vs. Resolution
BETA
MAXIMUM LEAKAGE
(dB)
SPECTRAL RESOLUTION
(BINS)
8 -63 2.25
10 -74 2.50
12 -95 2.75
14 -110 3.00
3-33