A device for determining the average particle size of particles, which are suspended in a liquid and flowing medium, via dynamic light scattering, comprising
- a) a throughflow cuvette for directing a liquid medium with specific viscosity and specific refractive index, which comprises particles in suspended form, in a laminar flow through a throughflow cuvette along a flow direction;
- b) a laser for radiating laser light of a specific wavelength in a radiation direction onto a liquid medium situated in the throughflow cuvette, a collimator being disposed between the laser and the throughflow cuvette;
- c) a temperature sensor for measuring the temperature of the liquid medium;
- and
- d) a detector for measuring the intensity of scattered laser light in the form of images, the detector being disposed perpendicular to the flow direction and at a specific angle of 10° to <180° relative to the radiation direction, and the detector
- i) comprising a beam splitter which deflects the scattered laser light onto a first and a second light-sensitive sensor, the two sensors being suitable for detecting images with respectively a specific number of pixels, and the two sensors being configured such that they detect scattered laser light alternatingly with a specific delay time as image;
- or
- ii) comprising a camera which has a light-sensitive sensor surface which is suitable for detecting images with respectively a specific number of pixels, the sensor surface being configured such that it detects scattered laser light with a specific delay time between two successive images as image;
- e) a data processing device for receiving the images measured at the detector, the data processing device being configured for implementing the following steps:
- 1) standardising the measured images so that the measured intensity of the laser light obtains the same average and the same standard deviation in the case of all images;
- 2) determining an offset and an angle of rotation of a pattern on at least one partial region of a first image relative to a pattern on at least a partial region of a second image following temporally thereafter and using this information in order to make the patterns of the two images congruent;
- 3) subdividing the congruent images respectively into many individual partial areas with respectively a specific number of pixels and averaging the brightness values of the pixels of the many individual partial areas;
- and
- 4) correlating the averaged brightness values of the pixels of the many individual partial areas of the first image with the averaged brightness values of the pixels of the many individual congruent partial areas of the second image, a correlation value being produced for each pair of congruent partial areas of the two images;
- 5) averaging over all obtained correlation values to form an average correlation value for the two images;
- characterised in that the device is configured for measuring, with a first and at least a second, different from the first, delay time, for indicating an autocorrelation function from the hereby respectively obtained, averaged correlation values, and for determining the average particle size by means of the autocorrelation function, the measured temperature of the liquid medium, the viscosity and the refractive index of the liquid medium, the wavelength of the laser light, the angle of the detector.