LASER-DOPPLERANORDNING FOER BESTAEMNING AV STORLEKEN HOS SFAERISKA PARTIKLAR SOM ROER SIG I ETT VAETSKEFLOEDE

PCT No. PCT/DK83/00054 Sec. 371 Date Jan. 16, 1985 Sec. 102(e) Date Jan. 16, 1985 PCT Filed May 18, 1983 PCT Pub. No. WO84/04592 PCT Pub. Date Nov. 22, 1984.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 ( theta ) 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 ( phi M) 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 ( phi R) is generated to indicate whether the resulting phase difference signal ( phi M) has been caused by a phase difference between the doppler signals exceeding 2 pi .