| 摘要 |
<p>In a laser-doppler-apparatus, the size of moving spherical particles in a fluid flow is determined by crossing two spatially separated laser beams (15, 16) to intersect each other under a given angle () in a measuring volume passed by a part of the fluid flow. By means of two photoelectric measuring detectors (17, 18) arranged in different spatial positions outside the measuring volume, scattered rays from a moving particle are detected in the form of doppler signals having different phase. The particle size is determined by generating a resulting phase difference signal (PHIM) from the signals from the two measuring detectors (17, 18). By combining the signal from one measuring detector (17) with the signal from a reference detector (19) positioned between the two measuring detectors, a phase reference signal (PHIR) is generated to indicate whether the resulting phase difference signal (PHIM) has been caused by a phase difference between the doppler signals exceeding 2pi. </p> |
