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BSA Flow Software Installation and User's Guide - CSI

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Figure 7-11 Doppler burst.<br />

Figure 7-12 Filtered signal with the DC-component removed.<br />

If more particles are present in the measuring volume simultaneously, we<br />

speak of a multi-particle signal. The detector current is the sum of the current<br />

bursts from each individual particle within the illuminated region. Since the<br />

particles are located r<strong>and</strong>omly in space, the individual current contributions<br />

are added with r<strong>and</strong>om phases, <strong>and</strong> the resulting Doppler signal envelope<br />

<strong>and</strong> phase will fluctuate.<br />

Most LDA-processors are designed for single-particle bursts, <strong>and</strong> with a<br />

multi-particle signal, they will normally estimate the velocity as a weighted<br />

average of the particles within the measuring volume. You should be aware<br />

however, that the r<strong>and</strong>om phase fluctuations of the multi-particle LDA signal<br />

add a phase noise to the detected Doppler frequency, which is very difficult<br />

to remove.<br />

7-16 <strong>BSA</strong> <strong>Flow</strong> <strong>Software</strong>: Reference guide

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