LDA is considered an absolute flow measurement method. By knowing the laser wavelength and the intersection angle between the laser beams, the calibration constant or fringe spacing can be easily calculated. It might thus seem unnecessary to calibrate an LDA system.
In the real world, tolerances on the lasers, optical fibres, lenses, and alignment introduce small deviations from the nominal fringe spacing. This leads to systematic errors on the measured velocities, which can be corrected for by calibration of the fringe spacing.
We offer optional calibration of the fringe spacing for 60 mm FiberFlow and FlowExplorer probes with a calibration uncertainty of 0.067% (coverage factor 2).
Calibrated probes come with a label showing the calibrated fringe spacing, a calibration certificate including the calibration data, a description of the calibration rig, an uncertainty analysis of the calibration procedure, and traceability references.