GB785563A - Refractometer - Google Patents

Abstract

785,563. Photo-electric control arrangements. ZEISS-STIFTUNG, C., [trading as ZEISS, C., [Firm of]]. July 27, 1955 [Aug. 10, 1954], No. 21719/55. Class 40 (3). [Also in Group XX] A critical angle refractometer comprises means for dividing light from a source into two beams of equal intensity one of which is focused upon the hypotenuse surface of a measuring prism which borders on the substance whose refractive index is to be measured and the other acts as a comparison beam, the two beams being directed to a photo-cell, a rotatable mirror being provided to direct light of different inclinations from the measuring prism on to the photo-cell, a balance being produced at an inclination of the mirror corresponding to the critical angle between the prism and the medium. As shown, light from the source 1 is directed by two mirrors 4, 4<SP>1</SP> to form two beams, that from the mirror 4 being concentrated by a lens 5 on the entrance surface of a prism 2 whose hypotenuse surface borders on a cell 3 containing the substance, e.g. a liquid, the refractive index of which is to be measured, light reflected from this surface being directed by an angularly adjustable mirror 6 to a telescope diaphragm 8. The beam from the mirror 41 is focused by a lens 5<SP>1</SP> on to a prism 2<SP>1</SP> similar to the prism 2 after passage through a movable optical wedge 18 and is re- . fleeted by an adjustable mirror 6<SP>1</SP> to a telescope diaphragm 8<SP>1</SP>. Light from these diaphragms is directed to a photo-cell 11 by lenses 12, 12<SP>1</SP> and mirrors, the beams being alternately interrupted by a rotating shutter 10. Current from the cell 11 is amplified at 13 and fed to an induction motor 14 which rotates the mirrors 6, 6<SP>1</SP> simultaneously and operates a recording pen 16. The motor 14 runs until the mirrors 6, 6<SP>1</SP> reach such a position that the two beams therefrom are of equal intensity when no alternating current is generated by the cell 11 and the motor stops, at which the angular position the mirror 6 corresponds to the critical angle of the surface bordering the prism 2 and the cell 3.