Improvements in apparatus for measuring by means of photoelectric cells the reflecting power of surfaces of substances

Abstract

Abstract 445,009. Photometric apparatus. ZEISS, C., [Firm of], Carl-Zeiss-Strasse, Jena, Germany.-(Assignees of Papirindustriens Forskningsinstitutt. Sk÷yen, near Oslo, Norway) Sept. 2, 1935, No. 24437. Convention date, Sept. 5, 1934. [Class 97 (i)] Apparatus for comparing the reflecting powers of surfaces comprises two photo-elec tric cells A, B connected together in parallel and each connected in series to a resistance 10, 18 and a common source of potential E, cell A being exposed alternately to light reflected by a standard surface and to light from the surface to be examined, and cell B being exposed to light from the common source 7, means 17 being provided to adjust the second beam until the potentials across the resistances are equal as measured by an electrometric instrument 20. The comparison beam obtained from a box 21 illuminated by lamp 7 passes through a tube 14 into an integrating sphere 13, and may be limited by an adjustable diaphragm 17. The measuring beam passes through aperture 5 in sphere 3 and is reflected into cell A by the surface 6 covering aperture 4. For white light diaphragm 17 is first opened fully and with a standard surface, such as one coated with barium sulphate, over aperture 4, diaphragm 16 is adjusted to give equal potential falls along resistances 10 and 18. The surface to be measured is now placed at 6 and diaphragm 17 adjusted, to give equaliy of potential, its reading giving the relative reflecting power of the surface. For coloured light, colour filters 25 on disc 26 may be rotated before cell A and a similar disc 29 rotated in the comparison beam each filter 25 being associated with a particular aperture 28 on disc 27 rotatable in the comparison beam. To ensure equal sensitivity of the cells for the various wavelengths the shaft driving the discs may also operate a potential changing arm 32 making contact with studs 33, or the light openings of filters 25 may be varied.

Inventors

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