Optics: measuring and testing – Photometers – Integrating spheres
Patent
1996-11-04
1998-05-05
Font, Frank G.
Optics: measuring and testing
Photometers
Integrating spheres
356446, 356 51, 250228, G01N 2100
Patent
active
057483043
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a measuring instrument for reflectometric measurements.
The invention specifically concerns a reflectometric measuring instrument in which the specimen under measurement is diffusely illuminated. In the literature this kind of method and apparatus is known under the name of ELREPHO (Electric Reflectance Photometer). Reflectometric measuring methods are employed when measuring the lightness, fluorescence, whiteness, translucence, opacity, brightness or other equivalent reflectometric optical properties of specimens. The invention quite particularly refers to a reflectometric measuring instrument intended to serve measurement of lightness of paper, cellulose and cardboard, i.e., of paper products.
At present, lightness of paper is in practice everywhere almost exclusively determined using a two-channel reflectometric measuring instrument manufactured by Zeiss. This instrument comprises a spherical measuring chamber, white inside, which is provided with two microscopes constituting a measuring channel and a reference channel. A standard specimen and/or the specimen to be measured is placed in the channel, and the light intensity of the object of measurement is detected with photometers disposed in the channels, and the detected light intensity values thus obtained are processed and, if necessary, amplified and compared with each other by means of a specific signal processing and calculating apparatus. The apparatus is calibrated with the aid of a standard specimen having a known reflectance value. The measuring method is in itself commonly known in the art and shall not be described in any greater detail in this connection; reference is made e.g. to the U.S. Pat. No. 07/793,261 and to the European Patent EP-229602.
However, the cited reflectometric instrument of prior art has proved unsatisfactory as the requirements of measuring accuracy have increased. Especially, when the aim is to regulate the illumination values of light sources, and thus the illumination of the measuring chamber e.g with the aid of a control stop, a situation is encountered in which the parts of the light produced by the light source (as a rule, white light) represented by various wavelengths, e.g. the proportion of UV light intensity to the intensity of visual light, will change owing to selectivity of the attenuator stop in different wavelength partial ranges. As a result, when the illumination of the measuring chamber is changed with the aid of the measuring stop, complete recalibration becomes necessary, to take taking the changed conditions into account. Furthermore, the results of measurement are no longer comparable with standard conditions, e.g. when the proportions of the light intensities of the UV range and the visible range change owing to attenuation. In other words, the measuring conditions fail to correspond to the standardized simulated daylight spectrum.
The problems just outlined have not be eliminated so far. These problems are particularly significant in connection with lightness measurements of paper products, and therefore the results of measurement obtained by the seller and receiver of paper often tend to differ, causing problems in the trade.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the drawbacks that have been pointed out.
Specifically, the object of the invention is to disclose a measuring instrument for reflectometric measurements in which the illumination can be regulated in a desired manner so that the proportions of different wavelength ranges in the light used for illumination are constant or changed, as desired.
The invention is based on the idea that the measuring instrument comprises at least one source of visible light, emitting light which has a wavelength substantially over about 380 nm, and a source of UV light, emitting light in the UV range having a wavelength substantially under about 380 nm. The wavelength of the UV range emitted by the light source is preferably in the range 300 to 380 nm.
The vi
REFERENCES:
patent: 4232971 (1980-11-01), Suga
patent: 4900923 (1990-02-01), Gerlinger
patent: 5182618 (1993-01-01), Heinonen
patent: 5384641 (1995-01-01), Imura
Conrex Automation Oy
Font Frank G.
Viena-Eisenberg Jason D.
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