Method and device for determining the particle size in a flowing sample

A device for determining the average particle size of particles in a flowing liquid medium by means of dynamic light scattering (DLS), the device comprising:

• an optically transparent channel,
• a laser aligned with the channel,
• at least one detector aligned with the channel at a scattering angle to the laser beam, which is set up to generate two two-dimensional spatially resolved images of a scattered light pattern with a specific delay time τ in succession and to output them as digital image data, wherein the two images form an image pair and wherein the at least one detector is also set up to generate at least two image pairs with different delay times τ, and
• an electronic evaluation unit for the digital image data, which is configured
• to bring the scattered light patterns of the images of each image pair into coincidence with each other at least by means of relative displacement and thereby to respectively determine a maximum correlation value and a displacement amount s,
• to determine a displacement velocity v from at least one of the displacement amounts s of the at least two image pairs and from the associated delay time τ, and
• to determine at least one coefficient of a correlation function g2(τ) that is dependent on the delay time τ from the correlation values of the at least two image pairs by means of a numerical fitting so as to derive a value for the average particle size from the at least one coefficient and thereby carry out a correction as a function of the determined displacement velocity v.