A near-infrared and/or visible optical analyzer which is able to measure the concentrations of material in industrial processes. The analyzer is equipped with a number of interference filters (9), mounted in a rotating filter wheel (11). The monochromatic radiation is reflected by the material moving along the optical window (27) of the analyzer. More than one type of detectors (29) are mounted in a detector head (30) to measure the reflected radiation in a wide wavelength range. The amplified and dark current compensated signal is processed by a microprocessor controlled circuit. The reflection optical standard (24) used as a reference in the analyzer periodically intercepts the radiation beam and radiation reflected from the standard is also impinging upon the same detectors. The reflection standard is mounted on a blade (22) rotated by a reduction gear mechanism (20). On the other side of the blade a so called absorption optical standard (25) is mounted, with the help of which the stable operation of the analyzer can be checked.
