GB1078181A - Apparatus for measuring the scattering power of transparent or translucent sheets - Google Patents

Abstract

1,078,181. Determining scattering power of plastics sheets; photometry. O. FAHR. Jan.12, 1965 [May 27, 1964], No.1379/65. Headings G1A and G1P. The scattering power of a transparent plastics sheet is measured by uniformly illuminating the inlet of an Ulbricht globe UG using an optical system to focus light through the inlet of the globe on to its outlet, a photo-electric detector being provided in an aperture of the globe in order to measure the light in the globe when either a white standard or a light trap is arranged at the outlet of the globe. The detector is a light-sensitive electron multiplier SEV, the output of which is indicated on a moving coil meter. With a sheet in the test position S between objective L 4 and the inlet of the Ulbricht globe UG, which is internally painted white, and with the standard white sheet over the outlet directly opposite the globe inlet, an indication of the total amount of light transmitted by the sheet can be made using the detector SEV located in an aperture at right angles to the direct light path. The circuit is adjusted so that the meter reads a full scale deflection for this particular detector output. The light scattered by the sheet is obtained by absorbing the light passing directly through the globe to the outlet by fitting over it the light trap e.g. Wood's Horn WH, the deflection of the meter giving the ratio of the scattered light to the light transmitted by the strip. The optical system ensures that light scattered by the apparatus is kept to a minimum and thus the ratio indicated by the meter represents the scattering power of the sheet. The optical system ensures a uniform illumination of the test object, and convenient dimensions for the globe inlet and outlet, allowing the light trap to be kept small. The white standard and light trap are mounted on a special changer slide. Filters are provided for measurements at different wavelengths. The D. C. voltage supply for the electron multiplier is from a stabilized mains source Fig. 2 (not shown) and the operating voltage is adjusted using two potentiometers.