Optics: measuring and testing – By shade or color – Trichromatic examination
Patent
1995-01-27
1997-10-21
Nelms, David C.
Optics: measuring and testing
By shade or color
Trichromatic examination
356408, 356414, 356416, 356419, 356420, 356425, G01N 2125, G01J 346
Patent
active
056802200
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and device for measuring optically the characteristics of a substance, such as, for example, the absorbance thereof.
BACKGROUND OF THE INVENTION
In the French patent FR-A-2,689,636 there is described a device for measuring the true optical absorbance of a substance contained in a cell. By means of optical switching means, light from a light source such as a halogen lamp whose frequency spectrum is known is transmitted successively to three optical filters of determined respective wavelengths. The first one corresponds to the isobestic point of the colored substance where the absorbance of the basic fraction of the substance is equal to that of its acid fraction and therefore independent of the pH value. The second one is in a part of the spectrum where the substance reacts most to the variations of the parameter to be measured. The third one is in a part of the spectrum where the absorbance of the substance substantially undergoes no variation. The light from each of the filters is so directed that it runs alternately through the cell containing the substance to be analyzed and an optical by-pass branch including for example a neutral filter, an optical by-pass fiber, or a reference cell, etc. The intensity of the successive emergent rays is measured and the various measurements are processed by a management and computing unit which determines optical characteristics of the substance, such as the true absorbance, which are independent of the possible fluctuations of the light source.
The method used provides accurate and reliable results, but the device implementing the method is relatively costly since it includes several optical switches whose unit price is relatively high.
SUMMARY OF THE INVENTION
The object of the invention is also to measure optical characteristics of a reacting substance contained in a transparent cell, such as its true absorbance, but the embodiment thereof is more simple and less costly than the prior art. It includes at least a light source, a first optical branch and a second optical branch allowing selectively passage of the light through the cell and outside it, an optical system for forming rays crossing the first optical branch and the second optical branch and a selective optical filter from an array of three selective filters, the first being centered on a first wavelength corresponding to the isobestic point of the reacting substance, the second one on a wavelength in a part of the light spectrum where the substance is the most sensitive, and the third one in another part of the spectrum where the substance is the least sensitive, means for measuring the intensity of the light crossing the optical system, a controller, and selection means controlled by said control set and an electric power pack.
The device is characterized by the selection means consisting of two optical shutters located respectively in the first branch and in the second branch, and of electric switching means.
The controller includes for example a control processor, an acquisition unit for acquiring the luminous intensity measuring signals and an interface set for controlling the selection means.
A first embodiment includes a single light source lighting the two branches and the optical system comprises by-pass means for directing towards the three filters the light rays which have crossed the first or the second branch, the measuring means include three detectors for measuring the light rays which have crossed the three filters, the electric means comprise elements for connecting intermittently the detectors to the controller set and a switch for connecting intermittently the lamp to the power pack.
According to another embodiment, the device includes three light sources, the optical system comprises by-pass means for directing the light from the sources respectively through the three selective filters and dividing means for applying the filtered light to the first and the second branches, the measuring means include, a single detec
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Delignieres Robert
Durand Christian
Eisenberg Jason D. Vierra
Institut Francais du Pe'trole
Nelms David C.
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