Abstract: A sample to be measured, a black reference and at least one reference having a color similar to that of the sample are exposed successively and cyclicly to the same incident light beam, the light beams which are reflected successively by the sample and the references are detected photoelectrically, the ratio of the intensities of the light beams reflected by a sample and one reference color on the one hand and by the black reference and a reference color on the other hand is established electronically, the second ratio is subtracted electronically from the first and a difference which is directly proportional to the brilliance of the color of the sample is automatically obtained during each exposure or measurement cycle at a determined measurement frequency (FIG. 1).

Abstract: A particulate product is transported on at least one tray vibrated at a pre-determined basic frequency. A product overload on the tray is avoided by monitoring its vibrations and detecting whether the amplitude of at least one harmonic sensitive to the load does or does not exceed a predetermined critical threshold.