Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1996-05-29
1998-07-07
Hantis, K.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
250574, G01N 2100
Patent
active
057777489
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an arrangement for determining the density and concentration of visible constituents in fluids, particularly for measuring the turbidity of motor vehicle exhaust gases. More particularly, the invention relates to a density determining arrangement of the type having a measuring chamber through which the exhaust gas flows, which measuring chamber is provided at two oppositely disposed points with a first light detector and a light source, and having an evaluation arrangement which evaluates the signal generated by the light detector as a measure of density and concentration.
Such a turbidity measuring device or opacimeter measures the attenuation of a light beam through a measuring chamber which is filled with the fluid to be measured or through which the fluid flows, with the light attenuation taken as the measure for the turbidity. The evaluation takes place according to the Lambert-Beer law which describes the light attenuation during passage through absorbing media. The assignee of this application distributes such a turbidity measuring device under the designation RTT 100/100 which serves to measure flue gas or soot in motor vehicle exhaust gases. The drawback of the known arrangements is that this turbidity measuring method fails for exhaust gases with low soot concentrations, as they are encountered with ever increasing frequency in engines or combustion systems of a more recent design. By means of structural or combustion engineering measures, the soot emission is reduced to such an extent that the accuracy of the opacimetric measuring methods is no longer sufficient. The reason for the limited accuracy for low soot concentrations lies in the principle of the measuring method, which is based on measuring a difference between a brightness signal and an attenuated signal, i.e., a difference between two signals which are almost identical in size.
From GB 22 52 621, a scattered light measuring method is known, wherein first a light beam is also guided into a fluid to be measured. The light portion which is scattered in different directions is captured and evaluated. In scattered light methods, a measuring signal is obtained which is proportional to the concentration of the absorbing medium. This scattered light method is suited particularly for low soot concentrations, but it is inferior to the opacimetric measuring method in the range of higher concentrations.
SUMMARY OF THE INVENTION
Advantages of the Invention
The arrangement according to the invention is characterized in that a second light detector is arranged outside lateral to the radiation path through the measuring chamber for capturing scattered light, and in that the evaluation arrangement evaluates the signal generated by the second light detector independently of the signal generated by the first light detector also as a measure for the density and concentration. Such an arrangement has the advantage that the advantages of the two known measuring methods are combined with one another, with a single measuring chamber being required and with it being possible to carry out the measurements of both methods simultaneously. In this manner, considerably greater accuracy is obtained over the entire range with a measuring complexity that is hardly any more extensive, and very high and very low concentrations can be measured with great accuracy.
Advisably, the measuring chamber is configured as a measuring tube through which the fluid to be measured flows during measuring, with the first light detector and the light source preferably being arranged at the two end faces of the measuring tube so that a measuring section is obtained which is as long as possible.
The second light detector (scattered light) is arranged in an advantageous manner substantially in the center between the light source and the first light detector on the side of the measuring chamber so that the scattered light can be captured at a small distance.
In order to be able to selectively supply the signals of the two light de
REFERENCES:
patent: 2873644 (1959-02-01), Kremen et al.
patent: 3510666 (1970-05-01), Topol
R. Lenk et al.: "Fachlexikon ABC Physik". Verlag Harri Deutsch, Zuerich and Frankfurt, 1974, p. 1599.
Hantis K.
Robert & Bosch GmbH
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