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Abstract

An apparatus for measuring components of liquid samples, such as milk samples, based on the ability of these components to absorb infrared radiation at certain frequencies. A single radiation beam is directed through a cuvette containing the sample, and the apparatus comprises a plurality of pairs of optical filters. Each of these pairs is associated with a respective one of the components to be measured and comprises a component filter for passing infrared radiation at a narrow frequency band at which the radiation absorbing ability of the said component is relatively high, and a reference filter for passing infrared radiation at a different narrow frequency band at which the radiation absorbing ability of the component is lower. A component of the sample is measured by successively positioning the filters of the associated pair of filters in the radiation beam between the radiation source and the cuvette, and the radiation passing the cuvette is detected by a detector, preferably a thermopile radiation detector of the monolithic type, and the content of the respective component is calculated on the basis of the signals received from the detector. The radiation beam is chopped by means of conventional chopping means, and each of the filters is preferably retained in the radiation beam in a period of time comprising a plurality of cycles of the chopping means.

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