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Alternative calibration method for Laser Doppler Anemometers

10.10.2006

A new, miniaturized calibration method for laser Doppler anemometers is presented which allows narrow measurement points to be accessed. For this purpose, a platinum wire mounted on a carrier is moved linearly through the measurement volume. The movement of the carrier is recorded by interferometry.

For the velocity measurement of fluids with Laser Doppler Anemometers (LDAs), a calibration device has been developed which – due to its small design – allows access to measurement points in measuring chambers which are difficult to reach (see Fig.1). Instead of the usual calibration glass discs rotating with known velocity, a measuring wire mounted on a carrier is moved linearly through the measurement volume of the LDA. The movement of the wire is recorded interferometrically with a resolution of 2 nm. In that way the fringe distance of the LDA measuring volume to be calibrated can directly be related to the wavelength of a He-Ne laser. The method allows LDAs in measuring chambers behind thick or curved glass windows to be calibrated with a required space of only a few millimeters. In addition, it is possible to calibrate reference beam–scattered beam LDAs which are measuring in forward direction as, for example, boundary layer sensors and line sensors, which cannot be calibrated by means of a rotating glass disc.

Rotating glass disc and linear motor with platin wire carrier for the calibration of LDAs

Figure 1: Rotating glass disc and linear motor with platin wire carrier for the calibration of LDAs

Contact person:

Volker Strunck, FB 1.4, AG 1.41, E-mail: volker.strunck@ptb.de