PROCESS FOR DETERMINING THE CONCENTRATION OF SUBSTANCES, DEVICE FOR IMPLEMENTING THE PROCESS, USE OF THE PROCESS FOR CHANGING THE CONCENTRATION OF A SUBSTANCE CONTAINED IN THE FLUID AND PLANT THEREFOR

摘要

The process for measuring the concentration of substances, in which one type of radiation lies in the region of the radiation absorption of the substances and another is not absorbed, operates with pulses of the same repetition frequency and equal pulse intervals. The detected electric signal, the median frequency of which corresponds to the reciprocal of the pulse interval, is filtered out by a filter. The concentration of the absorbent material is determined from the changes in amplitude of the signal filtered out. In a device for implementing the above process, filters are used of which the transmission regions are matched to the pulse repetition frequencies occurring. Considerable security against interference is attained owing to the interpretation of the measurement signal as a modulated signal. If the device is fitted in a plant with a feed device for mixing such a substance by chemical reaction, the concentration of the substance in the fluid can be precisely modified and in particular reduced in the sub-second time range. The plant is suitable for the denitrogenation of the exhaust gases of internal combustion engines.