Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-01-28
2001-02-27
Epps, Georgia (Department: 2873)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S222200, C250S437000, C250S297000
Reexamination Certificate
active
06194735
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a gas sensor and then particularly, but not exclusively, to a gas sensor with which the contents of a gas sample enclosed in a gas cell or cavity can be determined or analyzed, wherein the gas cell has the form of a block and the cavity walls or parts of said walls are highly reflective (mirror surfaces), wherein the cavity has an opening or some like means that functions to form incoming light rays into a light bundle, wherein the light bundle is intended to pass said cavity a predetermined number of times so as to define an optical analyzing path prior to the light rays being reflected by mutually opposite wall parts in a direction such as to pass through an opening or like means for outgoing light bundles, with the aid of at least three opposing, concave light-reflecting wall parts.
By the expression “openings or like means” is meant on the one hand that the cavity and mirror surfaces shall include at least one hole for receiving incoming light and at least one hole through which light exits, and that the light shall exit on one side of a mirror surface and shall enter on one side of a mirror surface on the other hand, in which application of the invention the mirror surfaces are whole. There is nothing to prevent light being allowed to enter on one side of a mirror surface and light to exit through one or more holes, or vice versa.
In addition to the aforesaid three opposing, concave light-reflecting wall parts, the cavity may also be delimited by further opposing light-reflecting wall parts. However, since the light reflected from these further wall parts will not contribute towards a better understanding of the present invention, the effect provided by said wall parts has not been described in this document.
A gas cell of this kind shall be coupled to a gas flow to be analyzed and to this end includes inlet and/or outlet openings, preferably in the form of tube or hose connections, although the principles of the invention can also be applied when the gas to be analyzed is allowed to diffuse into or out of the cavity.
A light source that has a frequency range adapted for determining the contents of the gas or gases under analysis, preferably an infrared light source, is connected to the gas cell and an opening, or like means, intended for the through passage of exiting, reflected light rays and located in wall parts of the cell, is provided with a wavelength selective filter, a spectral analyzing arrangement or like arrangement for evaluating the frequency-dependence of the light intensity and therewith determine the contents of the gas in question and/or the concentration of said content.
DESCRIPTION OF THE BACKGROUND ART
With regard to the earlier standpoint of techniques in the present context, reference is made to the subject matter of International Patent Publication PCT/SE96/01448 (corresponding to Swedish Patent Application No. 95 04020-0).
Reference is also made to this publication with regard to the definition of terms used in the present document.
With regard to the properties associated with the present invention, the teachings of the European Patent Publication 0 647 845 are also relevant with regard to the present standpoint of techniques, since it illustrates and describes a gas sensor that includes a gas cell which has a circular, concave mirror surface positioned opposite a concentrically orientated, circular-convex mirror surface, with the light source facing slightly to one side of the mutually coinciding centres of the mirror surfaces.
A gap in the convex mirror surface causes a slightly radially and outwardly directed light bundle with divergent light rays to be reflected alternately in concave and convex mirror sections, whereafter light rays are permitted to exit through a gap provided in the outer concave mirror surface, subsequent to having undergone a predetermined number of reflections and therewith having travelled through a predetermined optical light analyzing path of predetermined distance.
FIG. 6
of this prior publication illustrates an arrangement which is designed to enable the selection of one of two different optical analysis paths within the gas cell with the aid of separate light-ray exiting gaps and through a light-ray entering opening that is common to both analyzing paths.
It can be assumed that the described gas sensor is constructed so that its light receiving means is constructed to sense light rays that are coordinated to form a light bundle reflected in a convex mirror section in the gas cell and therewith a divergent light bundle.
Also forming part of the earlier standpoint of techniques is the arrangement of three partially spherical and opposing concave mirror surfaces designated “White” mirrors.
These mirrors are normally positioned at a relatively large distance from each other and the light source used is normally a laser light source.
A light bundle which contains more or less parallel light rays is reflected several times between the three opposing, spherically concave mirror surfaces, and when the last reflected light bundle is allowed to pass (adjacent the mirror edge) beyond a mirror surface, the light rays in the light bundle are received in a spectral analysis arrangement and evaluated in a known manner.
Also forming part of the earlier standpoint of techniques is the teachings of the Patent Publication U.S. Pat. No. 5,009,493. This publication describes an arrangement for a beam path in a multiple-reflection cell for measuring the absorption of light in a measuring gas. In the measuring arrangement, an entrance aperture is imaged on an exit aperture via an entrance aperture mirror, a field mirror and an exit aperture mirror.
This arrangement is improved in that the astigmatism of the imaging error is considerably reduced. For this purpose, the form of the aperture mirrors is approximately defined by an ellipsoid wherein the focal point spacing is approximately equal to half the distance between the entrance aperture and the exit aperture.
SUMMARY OF THE INVENTION
TECHNICAL PROBLEMS
When considering the fact that the technical deliberations which one of normal skill in this art must undertake in order to find a solution to one or more of the technical problems related to the analysis of gas and gas mixtures involve on the one hand the realization of those measures and/or sequence of measures that must be undertaken and on the other hand the selection of the means or those means required in to put these measures into effect make relevant the following technical problems in the development of the present invention.
When studying the known art referred to in the aforegoing, it will be seen that a technical problem resides in providing a gas cell that includes a gas inlet and/or a gas outlet or like means and that while using a light source which emits a light bundle into the cavity of the gas sensor or the gas cell causes the light rays to be reflected repeatedly between opposing concave wall parts that form either the whole of the cavity or a part thereof, and that is able to provide a predetermined number of reflections and therewith an optical analysis path of predetermined distance within the gas cell cavity, with the aid of a gas cell that has relatively small external dimensions and while applying the principles applicable to “White” mirrors but with the shape of the opposing mirror surfaces modified in accordance with the invention.
A technical problem resides in creating, with the aid of simple measures, conditions with regard to the mirror shapes of the concave wall-parts that will enable the light rays emitted by a light source to be converged and/or focused towards an outlet opening or like means even when the light bundle is initially pronouncedly divergent as it enters the cavity.
A further technical problem is one of realizing the advantages that are obtained when each of the three opposing mirror surfaces used has a domed shape with the dome smaller than half of a full ellipsoid and with the dividing plane of the dome located parallel with a chosen r
Burns Doane , Swecker, Mathis LLP
Epps Georgia
Thompson Tim
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