Photometric dust measurement

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Optical fine dust sensor for low dust concentrations. Measurement method with scattered light.

The photometric measurement of dust is a method for the determination of airborne particles and dust emissions . Measuring devices that work according to this principle record either the attenuation of a light beam ( extinction ) or its scattering . One advantage of the optical method is the virtually instantaneous output of the measurement result .

Process description

To measure the attenuation of the light in a dust-laden exhaust gas, a light beam that is split by means of a partially transparent mirror is partially passed through the exhaust gas. The other part of the light beam shines through a dust-free reference path. The attenuation of the light beam passed through the exhaust gas flow compared to the light beam that shines through the dust-free reference section is a measure of the dust content of the exhaust gas according to Lambert-Beer’s law . The measuring device is calibrated on site by assigning the corresponding dust load to a certain extinction.

The measurement can be carried out both in situ and ex situ with extractive sampling . The optical properties of the dust to be measured should be known. A possible attenuation of the light beam by the carrier gas is countered in practice by the selection of a suitable wavelength , such as the use of infrared light .

If the dust concentration in the gas is so low that the translucent light can transmit almost unhindered , measuring devices are used that work on the principle of scattered light measurement ( Tyndall effect ). A detector that detects the scattered light is attached at a sufficiently large observation angle, which can be, for example, 15 °, but also up to 90 °. Similar to the transmission measurement, the light beam is split in order to exclude the aging of the light source as a source of error.

literature

  • Karl-Wilhelm Bühne: Investigations into the directional dependence of photoelectric smoke density measuring devices. In: Dust - cleanliness. Air . 31, No. 7, 1971, ISSN  0949-8036 , pp. 285-290.

Individual evidence

  1. ↑ a b c d Franz Joseph Dreyhaupt (Ed.): VDI-Lexikon Umwelttechnik. VDI-Verlag Düsseldorf 1994, ISBN 3-18-400891-6 , pp. 1118–1119.
  2. ^ Günter Baumbach: Air pollution control . Springer-Verlag Berlin, Heidelberg, New York, 2nd edition 1992, ISBN 3-540-55078-X , pp. 220–222.
  3. ↑ a b VDI 2066 sheet 4: 1989-01 measurement of particles; Dust measurement in flowing gases; Determination of dust load by continuous measurement of optical transmission (Particulate matter measurement; measurement of particulate matter in flowing gases; determination of dust load by continuous; measurement of optical transmission). Beuth Verlag, Berlin, p. 2.
  4. ↑ VDI 2066 sheet 4: 1989-01 measurement of particles; Dust measurement in flowing gases; Determination of dust load by continuous measurement of optical transmission (Particulate matter measurement; measurement of particulate matter in flowing gases; determination of dust load by continuous; measurement of optical transmission). Beuth Verlag, Berlin, p. 3.
  5. ↑ VDI 2066 sheet 6: 1989-01 measurement of particles; Dust measurement in flowing gases; Determination of dust load by continuously measuring the scattered light with the photometer KTN (Particulate matter measurement; measurement of particulate matter in flowing gases; determination of dust load by continuous measurement of scattered light with the photometer KTN). Beuth Verlag, Berlin, p. 4.
  6. ↑ Wilhelm Dunkhorst, Hubert Lödding, Wolfgang Koch: Scattered light photometric measuring method for the time course of the PM 10 and PM 2.5 concentration in the outside air. In: Hazardous substances - cleanliness. Air . 68, No. 5, 2008, ISSN  0949-8036 , pp. 197-201.