MEASURING INSTRUMENT FOR REFLECTOMETRIC MEASUREMENTS

Abstract: A measuring instrument for reflectometric measurements, comprising a spherical measuring chamber (1) provided with a light source (2) and with a specimen aperture (3); a measuring channel (4) which has been provided with optics (5), with a photometer (6), with an optional stop (7) and with an optional filter (8); a reference channel (14) provided with optics (15), with a photometer (16), with an optional stop (17) and with an optional filter (18); an d a signal processing and calculating device (20s, 20c) for processing and comparing with each other the light intensity values observed by means of the photometers in the measuring and reference channels. As taught by the invention, the measuring instrument comprises at least one visible light light source (2s) which emits substantially light having a wavelength mainly over about 380 nm, and a UV light source (2u) which emits substantially light in the UV range having a wavelength mainly under about 380 nm, advantageously 300 to 380 nm.

Description: MEASURING INSTRUMENT FOR REFLECTOMETRIC MEASUREMENTS The present invention concerns a measuring instrument for reflectometric measurements, such as is defined in the preamble to Claim 1. The invention specifically concerns a reflec- tometric measuring instrument in which the specimen un¬ der measurement is diffusely illuminated. In the lit¬ erature this kind of method and apparatus is known under the name of ELREPHO (Electric Reflectance Photo¬ meter) . 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 the two- channel reflectometric measuring instrument manufac¬ tured 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 spec¬ imen to be measured is placed in the channel, and the light intensity of the object of measurement is detect¬ ed with photometers disposed in the channels, and the detected light intensity values thus obtained are pro- cessed 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 reflect¬ ance 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 American Patent US-07/793,261 and to the European Patent EP-229602. However, the cited reflectometric instrument of prior art has proved unsatisfactory as the require¬ ments of measuring accuracy have increased. Especially when the aim is to regulate the illumination values of light sources, and thus the illumination of the meas¬ uring 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, taking the changed conditions into account. Furthermore, the re¬ sults of measurement are no longer, e.g. when the pro¬ portions of the light intensities of the UV range and the visible range change owing to attenuation, compara¬ ble with standard conditions, i.e., the measuring con¬ ditions fail to correspond to the standardized simulat¬ ed daylight spectrum. The problems just outlined could not be elim- inated so far. These problems are particularly signifi¬ cant 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. 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 of which the illumination can be regulated in desired manner so that the proportions of different wavelength ranges in the light used for illumination are constantly as desired and/or unchanged. Regarding the features characterizing the invention, reference is made to the claims. The invention is based on the basic idea that the measuring instrument comprises at least one source of visible light, emitting substantially light which has a wavelength substantially over about 380 nm, and a source of UV light, emitting substantially 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 suitably substantially 300 to 380 nm. The visible light light source may be, for instance, a conventional light source emitting white light, e.g. an incandescent lamp, a gas discharge lamp or an arc lamp, which has been provided with a particu- lar filter for filtering off any light in the UV range. The visible light light source is further advantageously provided with a measuring stop for reg¬ ulating the illumination of the measuring chamber. The UV light light source is suitably a UV lamp, or in general any light source whatsoever which emits UV light, for instance a light source which has been provided with a filter or prism for filtering off any light other than UV light. The UV light source may likewise be provided with a stop. Thanks to the invention, the light used to illuminate the measuring chamber, e.g. substantially white light, can be regulated to a given desired inten¬ sity level separately, independent of the UV light intensity level. Furthermore, thanks to the invention, the intensity of the light in the UV range used to illuminate the measuring chamber can be regulated to a given desired level independent e.g. of the intensity value of the visible light. In general, thanks to the invention, regula- tion of the illuminating conditions of the measuring chamber can be implemented in a substantially more versatile manner, and in desired manner, conforming to high requirements imposed e.g. by paper lightness measurement. The invention is described in detail in the following with the aid of embodiment examples, refer- ring to the attached drawings, wherein Fig. 1 presents a schematic drawing showing a measuring instrument for reflectometric measurements according to the invention, that is mainly for paper, lightness mea¬ surements, and Fig. 2 displays the light intensity measured with an instrument as depicted in Fig. 1, plotted over wave¬ length, without and with additional UV light source. The measuring instrument comprises a spherical measuring chamber 1, provided with a light source 2 s , represented in the present embodiment by two visible light light sources 2__ . The measuring chamber further comprises a specimen aperture 3, so disposed that the illumination of the specimen inserted in the specimen aperture will be diffuse. The measuring instrument fur- ther comprises a special measuring channel 4, provided with optics 5 for directing the light reflected by the specimen to a photometer 6 which is part of the measur¬ ing channel; the measuring channel is further provided with an adjustable stop 7 for attenuating the light going to the photometer, and with a filter 8 for fil¬ tering the light going to the photometer. The measuring instrument further comprises a reference channel 14, provided with optics 15 for directing light from the measuring chamber to a photometer 16 which is part of the reference channel; the reference channel is in the embodiment here depicted furthermore provided with an optional stop 17 for attenuation of the light going to the photometer, and with a filter 18 for filtering the light going to the photometer. The measuring instrument further comprises a signal processing and calculating device, such as an amplifier and other signal process¬ ing means, 20 , for processing, and if desired amplify- ing, the electric signal which is proportional to the intensity of the light beam directed to the photometer, and a calculating means 20 , such as a computer, for processing and comparing the light intensity values observed wit the aid of the photometers in the measur¬ ing channel and in the reference channel, that is, the intensity values which said signals constitute. As taught by the invention, the measuring in¬ strument comprises at least one visible light light source 2 g emitting substantially light of wavelength mainly over about 380 nm, and a UV light source 2 u , emitting substantially light in the UV range having a wavelength mainly under about 380 nm, advantageously mainly 300 to 380 nm. The visible light light source 2 is symmetri¬ cally placed with reference to the measuring channel 4 and the reference channel 14; the measuring channel 4 and reference channel 14 are so placed that their axes pass through the centre of the measuring chamber and form an angle a with each other, α > 0 and a < 180°, e.g. < 45°, > 135°. The UV light source 2 u is further symmetrically placed with reference to the visible light light sources 2 s and to the measuring channel 4 and the reference channel 14. The visible light light sources 2_ consist of a conventional lamp emitting white light and they have in addition been provided with filters 21 for filtering off any light of the UV range. Moreover, the visible light light sources are provided with measuring stops 22 for regulating the intensity of the visible light. The UV light source 2 u is furthermore provided with a stop 23 for regulating the intensity of the UV light. The measuring stops of the visible light light sources 2_ are provided with drive means 24, adjustment of the latter taking place under control by the calcu¬ lating device 20. The corresponding adjustment of the stop coordinated with the UV light source 2 is provided with a drive means 25, subordinated to control by the computer. In the embodiment example now presented noth¬ ing else has been described but the adjustment of il- lumination in the measuring chamber of the measuring instrument; the measurement is accomplished in a way known in itself in the art, as is extensively docu¬ mented in the literature. Furthermore, the measuring instrument of the invention, and especially the regu- latiσn of illumination in the measuring chamber, is appropriate to be employed in connection with any re- flectometric measuring instrument whatsoever. Fig. 2 schematically illustrates the measuring chamber illumination determined in a measuring instru- ment according to the invention, plotted over wavelength, when two light sources emitting visible light only are used; the respective graph has been labelled UV OFF. The figure further displays the cor¬ responding graph obtained when for illumination of the measuring chamber there has in addition been used a UV light source emitting substantially light of the UV range, with wavelength mainly between 300 and 380 nm; this curve is labelled UV ON. Scrutiny of Fig. 2 reveals that the measuring instrument of the invention conforms rather well to he values of illumination simulating daylight, in the UV range as well. The embodiment examples are merely meant to illustrate the invention, without in any way re- stricting it.

Claims: CLAIMS 1. A measuring instrument for reflectometric measurements, comprising a spherical measuring chamber (1) provided with at least two light sources (2) and with a specimen aperture (3) so that the illumination of the specimen placed in said specimen aperture will be diffuse; a measuring channel (4) which has been provided with optics (5) for directing the light re- fleeted by the specimen under measurement to a photome¬ ter (6) which is part of the measuring channel, with an optional stop (7) for attenuating the light going to the photometer, and with an optional filter (8) for filtering the light going to the photometer; a refer- ence channel (14) provided with optics (15) for direct¬ ing light from the measuring channel to a photometer (16) which is part of the reference channel, with an optional stop (17) for attenuating the light going to the photometer, and with an optional filter (18) for filtering the light going to the photometer; and a signal processing and calculating device (20,21) for processing and comparing with each other the light intensity values observed by means of the photometers (6,16); characterized in that the measuring instrument comprises at least one visible light light source (2 g ) which emits substantially light having a wavelength mainly over about 380 nm, and a UV light source (2 u ) which emits substantially light in the UV range having a wavelength mainly under about 380 nm, advantageously 300 to 380 nm. 2. Measuring instrument according to claim 1, characterized in that the instrument comprises two visible light light sources (2 s ), the light emitted by them having a wavelength over 380 nm. 3. Measuring instrument according to claim 1 or 2, characterized in that the visible light light sources (2 ) are provided with filters (21) for filter- ing off light in the UV range which has a wavelength under 380 nm. 4. Measuring instrument according to any one of claims 1-3, characterized in that the visible light light source is provided with a measuring stop (22). 5. Measuring instrument according to any one of claims 1-4, characterized in that the UV light light source (2 u ) is provided with a stop (23).

Inventors: HEINONEN AIMO, HEINONEN, AIMO
Applicants: CONREX AUTOMATION OY, HEINONEN AIMO, HEINONEN, AIMO
Application year: 1995
Main classification: G01N21
IPC codes: G01J1, G01N21