BSA Flow Software Installation and User's Guide - CSI

u
v
2
2
=
=
∑
∑
tU
tV
2
2
− 2U
− 2V
∑
∑ t
∑
∑ t
Update derived quantities:
σ
u
=
u
2
σ
v
=
v
tU
+ U
tV
+ V
2
2
2
∑
∑
t N
⋅
N −1
t N
⋅
N −1
Update confidence limit values (assuming normally distributed velocities):
ε
σ
96
N
( σ u ) 1.
96
σ u
2N
Estimation of the integral time scale τI
u
( U ) = 1.
( V )
ε = ( )
ε
σ v
= 1.
96
N
ε σ v = 1.
96
σ v
2N
The factor1.96 gives 95% confidence.
All the above expressions are valid for statistically independent, or
uncorrelated, velocity samples. A way to ensure that the samples are
uncorrelated is to use the controlled dead time acquisition mode of the BSA
processor, with a dead time equal to 2 *τI.
To estimate τI, the Spectrum/Correlation add-on for BSA Flow Software can
be used. A step-by-step procedure is given below:
Define a BSA Flow Project with the BSA data collection mode set to
”Burst”
Add a Correlation object.
Add a 2D Plot to the Correlation object. Define the X axis as Time and the Y
axis as Correlation. Set Normalize ”On” in the Correlation properties.
Make an acquisition with high data rate, and a large number of samples
(preferably 10000 or more)
Look at the Correlation plot. It will typically have a shape similar to this:
BSA Flow Software:Reference guide 7-105