Abstract: Apparatus and process provide qualitative and quantitative analysis of sample constituent(s) in a stream of fluid, relatively free from qualitative ambiguities and quantitative zero displacements due to slowly changing contamination in the measurement stream. Slowly changing zero displacement of a continuous measurement signal -- caused by slowly changing contaminant concentrations in the stream -- is cancelled out by deriving two continuous versions of the measurement signal, both being time-distorted, and continuously manipulating the two versions as by subtraction.One of the two time-distorted versions serves as a primary or "main" signal; this main signal version is distorted in such a way that the time distortion of the other signal version is roughly symmetrical with respect to the main signal version, to improve measurement accuracy when the rate of zero displacement is nonlinear. In the case of spectral analysis, particular advantages lie in removal of misleading "background" spectral components.

Abstract: Apparatus and process provide qualitative and quantitative analysis of sample constituent(s) in a stream of fluid, relatively free from qualitative ambiguities and quantitative zero displacements due to slowly changing contamination in the measurement stream. Slowly changing zero displacement of a continuous measurement signal -- caused by slowly changing contaminant concentrations in the stream -- is cancelled out by deriving two continuous versions of the measurement signal, at least one being time-distorted, and continuously manipulating the two versions as by subtraction. In the case of spectral analysis, particular advantages lie in removal of misleading "background" spectral components.

Abstract: An interferometer having two spaced apart but parallel composite beams passing through respective fluid containing cells with the radiation output of these cells being imaged onto a detector. The optics at one end of the cells are made movable with respect to the optics at the other end of the cells in order to accommodate various size cells and materials, and to simplify optical alignment of the interferometer without disturbing the focusing properties of the instrument.