BSA Flow Software Installation and User's Guide - CSI

Figure 7-21: The effect of changing the azimuth angle, ψ, and the angle between
the incident beams, ϑ, on the slope of the diameter–phase relationship.
Changing ϑ affects both the slope of the diameter phase curve and the
velocity-frequency relationship.
ϑ can be changed in two ways:
• Changing the focal length of the front lens of the transmitting optics.
• Changing the beam separation.
The 55X Modular LDA Optics system, the 60X FiberFlow series and 65X60
FlowLite all have exchangeable front lenses of different focal lengths.
Changing the beam separation is a more convenient method of changing ϑ
since the working distance remains unaffected. The 55X82 Beam Translator
is meant for this purpose. This unit fits the 55X-series optical modules and
the 85 mm FiberFlow probes (models 60X80, 60X81, 60X82 and 60X83).
Also with the 60 mm diameter probe a change in beam separation can be
achieved using the special 41X805 Beam Displacer for 60X60, 60X62,
60X64 and 60X66, and 41X806 Beam Displacer for 60X61, 60X63, 60X65
and 60X67.
Handling the In Figure 7-22 the phase difference is illustrated for three different particles
of
2π ambiguity increasing size. While the phase difference for the first two particles is
within 2π (= 360°), the third particle falls beyond this range.
Figure 7-22: The 2π ambiguity.
From measuring the phase difference between the Doppler bursts received
by the two detectors alone there is no way to tell whether the diameter is D 3
or D 3 ’ (corresponding to the phase difference –2π). This is referred to as the
2πambiguity.
BSA Flow Software:Reference guide 7-27