Abstract: A method for controlling production process by performing near-infrared absorptiometric analysis by simple procedures in an accurate manner, in which control of production process step can be realized at a high accuracy by simple operation based on the thereby obtained analytical results, the said method comprising taking each absorbance spectrum for a plurality of standard samples in an analysis range including near-infrared region, calculating the average intensity and standard deviations for each of selected wave lengths to construct a data base, taking an absorbance spectrum in the said analysis range for each of analysis samples and comparing it with the data base in order to judge whether or not the intensity of the absorbance spectrum is within an assumed tolerance limit determined based on the stored standard deviations of the standard samples in the data base to thereby obtain control data by comparing, when wave lengths at which the observed intensity is outside the tolerance limit are present, thes

Abstract: A process for producing a polyester of uniform quality, in which a slurry of powdery aromatic dicarboxylic acid in a liquid diol is prepared and the resulting slurry is processed through an esterification step and a polycondensation step in the presence of a catalyst, is provided by performing the reactions in the esterification and the polycondensation in a stabilized condition, which process comprisesrecycling a liquid containing the unreacted diol and the catalyst separated from the reaction mixture in the polycondensation step back to the esterification step as recycling liquor,detecting the concentrations of diol, diol condensation product, catalyst and water in the recycling liquor in the course of being recycled back to the esterification step by a near infrared spectrophotometer of a noise level of at the highest 50.times.10.sup.-6 Abs with a wave length repeatability of 0.

Abstract: A sample to be analyzed is taken from a flow line of a production process and transferred through a slender pipe to an analyzing device. The transfer is accomplished using a pressurized liquid with a segment gas being interposed between the sample and the pressurized liquid. The sample may be fed directly or after mixing with a diluting liquid in a mixing chamber. Samples may be taken at regular and constant time intervals and transferred to the analyzing device stably and over predetermined periods of time.