Design And Application For System Of Measurement Of Whiteness

The sections for producing the materials, such as building materials, chemical engineering, spinning, paper and food...etc., the whiteness is directly or indirectly one of the index signs for many products quality examination. The traditional method of eyesight for determining the intensity of light is replaced by the physics principle for determining intensity of light, then the techniques and the instrument which are used to measure the whiteness are gradually in unify and perfect. Meanwhile development of chip stimulated the appearance of the high performance, low cost MCU. Hereafter, design for the small-sized, standardized, intellectualized, high accuracy, high stability of the instrument for measuring the whiteness becomes the very realistic demand. The new instrument carries on the quantitative analysis for the attribute of the special color. So it involves more extensive and basic knowledge concerning three aspects of the colourity study, the luminosity study and the radiativity study. We usually think that reflectivity of the visible spectrum is very high and the reflectivity curve is flat, then the material is white. But many materials of it descend sharply in the blue spectrum area, thus make the materials get yellow, so we described the whiteness of the paper in the past through measuring reflectivity of the blue spectrum. Although increase the blue dyestuff can raise the reflectivity of the blue spectrum, which lowers the total reflectivity. Use the fluorescence to increase the material whiteness also brought the complicated spectral luminosity problem. Whiteness measurement may be two ways: either is the single spectrum method or is the several spectrum method according to the spectrum composition; according to the principle of measurement it may also be two ways: the spectral luminosity method and the direct reading of stimulating method. The common calculation formulas contain the whiteness formula of Hinter, the whiteness formula of Gancy, the whiteness formula of blue light, the whiteness formula of the even factor of radiant luminosity. This design, I adopted the method of single spectral luminosity: I choose spectrum of wave-length 457 nm, and formula of whiteness is W=αB457,αis a coefficient, and it is determined by error from measurement of single spectrum and from imperfect design. Use comparative measurement, we can evaluateα. Halogen lamp matches the light source of A within the scope of certain voltage in view of its emission line. The light source of A is abundant of UV spectral emission, and it can be used to measure fluorescence spectrum as the light source. Put a filter of 457 nm in front of halogen lamp, and make outward light identical with emission spectrum: central wavelength lies at 457±0.5 nm, half breadth is 44 nm, to imitate the light source D65 for the whiteness measurement. And add a orange filter of 565 nm in the light beam, make its wavelength equals to the 565 nm for measuring lightness. The system includes two parts: system of light and system of circuit. ⅰ) System of light is composed of light source ,integral ball, sample table, photoelectric detector…The halogen lamp, convex lens, non-ultraviolet flashboard, reconcilable ultraviolet flashboard, reconcilable ultraviolet filter, flashboard capable of choosing spectrum and the hole in integral ball make up of coaxal light system. Light from the halogen lamp becomes parallel though convex lens. The parallel light runs though non-ultraviolet flashboard, the ultraviolet is excluded. Also the parallel light runs though the reconcilable ultraviolet flashboard, either is ultraviolet included or not. Subsequently, the parallel light runs though reconcilable ultraviolet filter, partially is ultraviolet included. Then we can use the light to measure fluorescence whiteness. The hole let light into the integral ball ,and it stands upright normal of sample table. It can be seen as perfect diffusing light source and instrument for mixing light equably, appended with light source, detector. The integral ball is mainly a hollow ball made in aluminium and plastic. Its inner-wall is painted equably by several layer of litmusless and diffusing material. The ball has the other holes, which are ready for detector and light source. To prevent the light from radiating the detector, the inner ball is put on a screen.