Method and apparatus for determining the quantity ratio of two components of a multi-substance mixture

摘要

A method for determining the quantity ratio of two components of a multi-substance mixture whose absorption bands are adjacent to each other and overlap comprises using an interference filter which is rotated in a uniform rotation about a first axis through the filter plane which forms with a perpendicular erected on the filter plane a fixed angle beta which is not equal to zero. The filter is rotatably arranged about a second axis through the filter plane and the method is characterized by adjusting the angle alpha which the axis of rotation forms with the ray in the range of beta is less than alpha so that a signal corresponding to the first derivative of the spectral intensity distribution of the radiation transmitted by the substance mixture just passes through zero and a quantity correlated with this angle is used as a measure of the quantity ratio. The radiation modulator for determining the quantity ratio includes a housing having an opening for the passage of the light ray therethrough and a filter in the housing in the path of the beam. The filter is mounted for rotation about a first axis comprising the axis of the filter and is mounted for pivoting about a second axis also going through the filter. The first axis is such that the area normal thereof forms with the first axis a fixed angle beta and the first axis is rotatable about the second axis and an angle alpha is formed between the first axis in the ray direction which may be read and indicated and the filter is adjustable to vary the angle.