Optics: measuring and testing – By shade or color – With color transmitting filter
Patent
1988-10-31
1990-12-04
Evans, F. L.
Optics: measuring and testing
By shade or color
With color transmitting filter
356315, G01N 2172
Patent
active
049749633
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for analysing a gaseous composition by flame spectrophotometry.
It relates more particularly, but not exclusively, to the construction of a portable apparatus of this kind which makes it possible to measure instantaneously, with direct reading, the proportion of gaseous elements contained in the ambient air, for example polluting elements or even war gas.
It is known generally that flame spectrophotometry is a method which consists in making a spectrographic analysis of the radiation produced by the flame of a gas mixture including the elements to be analyzed. This analysis may be made by isolating the characteristic radiations of the desired elements and measuring the intensity of these radiations photometrically. Through previous calibration of the apparatus on gaseous compositions of known concentration, it becomes possible to obtain the proportion of a desired element in a gaseous mixture, directly from this measurement of intensity.
Thus, in the case of analysing the ambient air, the flame is usually obtained by combustion, inside a burner of a constant flow rate hydrogen stream in the air flow to be analysed.
The invention relates more particularly to the construction of a self-contained portable analysis apparatus, however of high precision, based on this method.
Now, because of the nature of the elements used and, in particular, the hydrogen source, the means for regulating the flow rate which are associated therewith, the burner, the optical system used for the spectrographic analysis, the optoelectronic measurement circuits and the source of electric energy required for operating the whole, such a construction seems at first hand difficult to conceive.
To solve this problem, the invention proposes first of all, for the hydrogen production, using a hydrogen accumulator of the type in which the release of hydrogen is obtained by the heating of elements such as hydrogen impregnated lanthanum-nickel granules contained in a small volume interchangeable cartridge.
This solution which makes it possible to overcome the problems of size and weight of the hydrogen source involves on the contrary for heating the lanthanum granules to the prescribed temperature, a relatively high electric power consumption requiring, in order to maintain sufficient autonomy, relatively bulky and heavy electric power sources. In other words, the advantage obtained by adopting the above hydrogen generator is offset by the size of the electric source which it requires.
Now, it has proved that the hydrogen flow which is required for ensuring operation of the analysis device is relatively small and does not require continuous heating, of constant power, of the hydrogen generator.
On the basis of this discovery the invention proposes, in order to limit the heating power to strictly what is necessary making the heating device dependent on the hydrogen pressure reigning upstream of the regulator which supplies the burner with hydrogen at a constant flow rate. In fact, the part of the hydrogen circuit situated upstream of this regulator forms a buffer volume in which the hydrogen pressure may vary above a threshold value in a pressure range appropriate to that required by the regulator so as to maintain the hydrogen flow constant. The control used will then serve for maintaining the hydrogen pressure reigning inside said volume within said pressure range by continuously or discontinuously adjusting the electric power applied to the heating device.
Advantageously, the flow rate regulation device may comprise, in series, a membrane pressure reducer and a flow regulator. In this case, pressure detection may be accomplished by detecting the position of the membrane of the pressure reducer.
In an advantageous embodiment of the invention said flow regulator device comprises a hollow preferably cylindrical body with two opposite coaxial orifices, namely an access orifice for connecting to the hydrogen accumulator and an outlet orifice connected to the burner and an internal dividing wall, perpendicular
REFERENCES:
patent: 3791743 (1974-02-01), Cody et al.
patent: 4099883 (1978-07-01), Berger et al.
Gilles Guene
Patrick Bleuse
Pierre Clausin
Drucker William A.
Evans F. L.
Proengin
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