GB848243A - Improvements in and relating to refractometers - Google Patents

Abstract

848,243. Photo-electric refractometer. BELLINGHAM & STANLEY Ltd. Dec. 23, 1958 [Oct. 28, 1957], No. 33515/57. Class 40(3). [Also in Group XX] A refractometer comprises a Littrow prism formed of, or adapted to contain, the medium of which the refractive index is to be measured, means for projecting a parallel beam of radiation on to the prism, and means for rotating the prism to adjust the direction of the beam of radiation leaving the prism. In use the prism is preferably adjusted so that the radiation leaving the prism returns along the same path as the incident beam. As shown in Fig. 1 a parallel beam of monochromatic radiation is incident on the Littrow prism 1 which is mounted on a platform 12, Fig. 2, rotatable about an axis 3 by adjustment of a screw 16 and nut arrangement of which the screw is connected to the platform by a flexible band 13. In the light path is disposed a mirror 6 which deflects the radiation to reflecting surfaces 8, 9 which direct the beam on to photo-cells 10, 11. The drum, which is calibrated to give direct readings of refractive index, is now adjusted until the photo-cells give equal outputs in which case the prism is in the position of minimum deviation. Alternatively the beams from the reflecting surfaces 8, 9 are alternately and rapidly directed on to a single photo-cell. A servo system may be provided which is actuated by the signals from the photo-cell or cells and adapted automatically to rotate the prism to a balancing position. This servo system may also be arranged to operate a recorder, for example to provide a record of refractive index at a fixed wave length for a liquid which continuously flows through the prism.