BSA Flow Software Installation and User's Guide - CSI

Properties of the Advanced Spectrum object
Figure 6-57 Properties of the Advanced Spectrum object
The properties are identical to those of the Spectrum object, except for
“Noise reduction”.
Note It is recommended to keep Noise reduction Off during acquisition, and to
switch it On when running off-line.
For the remaining properties, please refer to section 0.
Output from the Advanced Spectrum object
Please refer to section 0
Presenting results from the Advanced Spectrum object
Please refer to section 0
Background information and references
The Advanced Spectrum add-on is based on a new algorithm, the Refined
Sample and Hold algorithm.
With this algorithm, turbulence spectra can be correctly estimated to
frequencies above the mean data rate, without sacrificing computing speed.
The upper frequency limit is thus 10-20 times higher than that of the
traditional sample-and-hold technique. One advantage of this is that correct
spectra can be obtained without excessive seeding of the flow. Two papers
presenting the theory and an experimental verification of the algorithm were
presented at the 10 th International Symposium on Applications of Laser
Techniques to Fluid Mechanics in Lisbon, Portugal, July 2000. See
http://in3.dem.ist.utl.pt/downloads/lxlaser2000/pdf/03_2.pdf and
http://in3.dem.ist.utl.pt/downloads/lxlaser2000/pdf/03_5.pdf.
In a comparison made at the 1998 Lisbon Conference on laser anemometry,
two algorithms stood out as producing better results than other ones: the
refined sample an hold technique and the improved Slot Correlation
technique. The latter gives slightly lower variance of the spectrum, but is
much slower than the refined sample and hold technique, and is therefore not
practical for on-line processing purposes.
6-62 BSA Flow Software: Options and Add-ons