A laser—Doppler sensor for flowrate measurements

Abstract

In many fields of research, as well as in industrial and medical applications, precision, low volumetric flowrate measurements are required with instruments which function reliably over a wide measuring range. This paper describes an instrument that utilizes laser—Doppler anemometry as the basis for a measuring device that is able to cover a measuring range for liquid flows of up to 1:6500. Measurements over the entire range are accomplished without range switching; in addition, very low volume rate measurements can be obtained, e.g. measurements as small as 5 × 10 −2 cm 3 min −1 . The basic priciples of the measuring device are explained and it is shown that the actual velocity of the pipe flow can be utilized, in all kinds of fluids, to obtain the volumetric flowrate. If the shape of the velocity profile is known, no calibration of the instrument is required. The measuring procedure is demonstrated for laminar and turbulent flow regimes. Applications in these ranges are given. In this paper, the practical realization of a laser—Doppler sensor is described and its application in verification measurements is shown. Suggestions for further developments and applications are made.