Optics: measuring and testing – For light transmission or absorption
Reexamination Certificate
2001-01-27
2003-05-06
Lee, John R. (Department: 2881)
Optics: measuring and testing
For light transmission or absorption
Reexamination Certificate
active
06559945
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a method of measuring the spectral absorption of a body placed between a source for emitting electromagnetic radiation and a detector for detecting said radiation, the method consisting in performing the following steps:
emitting said electromagnetic radiation in a determined spectral range towards said body;
filtering the electromagnetic radiation; and
detecting the electromagnetic radiation attenuated by the absorption due to the body and deducing therefrom a measure of the spectral absorption of said body.
The invention also relates to an apparatus for implementing the method and it applies most particularly to gases.
BACKGROUND OF THE INVENTION
Conventionally, the spectral absorption of a body placed between a source for emitting electromagnetic radiation and a detector of said radiation is measured by:
emitting said electromagnetic radiation in a determined spectral domain by means of an apparatus
10
shown in FIG.
1
and comprising a source
12
and a body
14
that receives the radiation;
filtering the radiation by means of a filter
16
, e.g. a filter of the type that is electrically tunable over all or part of the spectral domain under consideration; and
detecting the electromagnetic radiation as attenuated by the absorption due to the body by means of a detector
18
, and in deducing therefrom a measure of the spectral absorption of said body.
This procedure is applied, for example, to the field of spectroscopy as applied to analyzing gas.
Document EP 0 608 049 illustrates one such example.
To measure the spectral absorption of a body such as a gas, for example, the filtering step makes use either of a plurality of static interference filters each tuned to a narrow range of wavelengths which, once united, cover all or part of the spectral domain under consideration, or else as mentioned above, it makes use of a filter that is tunable over all or part of the spectral domain under consideration.
In the first case, it is necessary to provide a mechanism such as a cylinder, for example, on which the filters are mounted, so that there is only one electromagnetic path, or else to provide a kind of electromagnetic mixer which shares the electromagnetic radiation amongst a plurality of static filters.
With an electromagnetic mixer, is it also necessary to have one detector associated with each filter.
Thus, such a solution is relatively complicated to design and implement and it is costly.
In the second case, the elements of the apparatus are much fewer since a single filter is present and there is only one electromagnetic path to be taken into consideration.
However, it is difficult to find electrically tunable filters in the trade that are suitable for the intended applications, and the design of an electrically tunable filter is no easy task.
Document U.S. Pat. No. 5,703,689 describes apparatus for measuring the spectrum of incident radiation by means of a broad-band optical detector which measures the intensity of incident radiation that has passed through a narrow-band optical element. The band of the optical element can be shifted over a wavelength interval determined by modifying its temperature. The optical element in the form of a semi-conductive film acts as a filter. The spectrum of the incident radiation is obtained by differentiation of the intensity measured by the detector relative to temperature. The filtering and detection steps are thus separate and implemented by two different means, respective optical elements acting as a filter and as a detector.
SUMMARY OF THE INVENTION
From the above it would appear to be advantageous to be able to measure the spectral absorption of a body in a manner that is more simple than in the prior art.
The present invention thus provides a method of measuring the spectral absorption of a body placed between a source for emitting electromagnetic radiation and a detector for detecting said radiation, the method consisting in performing the following steps:
emitting said electromagnetic radiation in a determined spectral range towards said body;
filtering the electromagnetic radiation; and
detecting the electromagnetic radiation attenuated by the absorption due to the body and deducing therefrom a measure of the spectral absorption of said body, the method being characterized in that the filtering and detection steps are implemented by a detector of the quantum type.
It is thus no longer necessary to use a filter for the filtering step since the quantum detector itself performs this function, thereby simplifying the measurement technique.
More precisely, the quantum detector presents spectral sensitivity having an absorption front at a given wavelength that corresponds to the bandage of said detector and it delivers a signal corresponding to the electromagnetic energy received by said quantum detector. The method then consists in using the absorption front of the spectral sensitivity of the quantum detector to deduce therefrom the measure of the spectral absorption of the body.
In the invention, the method consists in performing the following steps:
moving the absorption front of the spectral sensitivity of the quantum detector from a position corresponding to a wavelength &lgr;
0
towards a position corresponding to a wavelength &lgr;
1
, both of which wavelengths are included in the spectral range of the emitted electromagnetic radiation; and
combining the signals delivered by the quantum detector for the respective positions of the absorption front corresponding to the wavelengths &lgr;
0
and &lgr;
1
and deducing therefrom the measure of the spectral absorption of the body in the wavelength interval lying between &lgr;
0
and &lgr;
1
.
The term “combining the signals” covers any mathematical operation that puts the signals into a mutual relationship so as to be able to deduce therefrom a measure of the spectral absorption of the body.
For example, the method can consist in taking the difference between signals delivered by the quantum detector for each of the positions of the absorption front corresponding to wavelengths &lgr;
0
and &lgr;
1
, or in forming the ratio of the signals delivered by the quantum detector for each of the positions of the absorption front corresponding to the wavelengths &lgr;
0
and &lgr;
0
.
The absorption front of the spectral sensitivity of the quantum detector is obtained by varying a physical parameter on which the position of said absorption front depends.
The invention is of particularly advantageous application when the body is a gas.
In the more particular field of spectroscopy as applied to analyzing gas, the invention also provides a method of determining the calorific value of a gas constituted by fuel components, characterized in that it consists in performing the following steps:
emitting said electromagnetic radiation through said gas in a determined spectral range in which the gas presents absorption;
detecting the electromagnetic radiation attenuated by the absorption due to the fuel components by means of a quantum detector which presents spectral sensitivity having an absorption front corresponding to the bandgap of said detector, while successively moving said absorption front of the detector to positions corresponding to successive wavelengths &lgr;
0
, . . . , &lgr;
n
included in the spectral range, said detector delivering a signal S(&lgr;
i
) corresponding to the electromagnetic energy received by the quantum detector at each of the positions of the absorption front at wavelength &lgr;
i
;
combining the successive signals delivered by the quantum detector S(&lgr;
i
), i=0, . . . , n so as to isolate the spectral absorption of the fuel components over each wavelength interval (&lgr;
i
; &lgr;
i+1
); and
comparing the above-obtained signal combinations with signal combinations previously obtained during a calibration step on a reference gas of known composition, and deducing therefrom the calorific value of the gas.
For example, the method consists in taking the difference S(&lgr;
i+1
)−S(&lgr;
i
)
Lee John R.
Schlumberger Resource Management Services, Inc.
Smith II Johnnie L
Straub Michael P.
Straub & Pokotylo
LandOfFree
Method for measuring spectral absorption in a body and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for measuring spectral absorption in a body and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for measuring spectral absorption in a body and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3070051