GB389214A - Improved instrument for comparing the relative intensity of radiant energy - Google Patents

Abstract

389,214. Photometric apparatus. GUELKE, R. W., 89, Crescent Road, Crumpsall, Manchester. Dec. 31, 1931, No. 36031. [Class 97 (i).] The intensities of two beams of light are compared by creating electric currents of intensities corresponding to the light intensities of the two beams, these currents being balanced against each other and the resultant current being caused to operate a light-regulating means in the path of one of the beams, the regulating means being operated by the moving system of the current-measuring device. In the form shown, light from a source L falls on a rotary shutter R having alternate reflecting and transparent sectors. The reflected light passes through the material X of which the light-transmitting power is to be measured and the light transmitted by the shutter R passes through a light-regulating device W such as an absorption wedge, both beams being then incident on a single photoelectric cell P. The output from the cell, after amplification, is rectified by a commutator C on the shaft of the rotary shutter R and is supplied to a galvanometer &c. G. the moving system of which carries the wedge W. The wedge is thus automatically adjusted until the intensities of the two beams are equal. Instead of using a commutator, a motor generator may be employed to drive the shutter R, the alternating current from the generator being supplied to the field windings of a dynamometer, the moving coil of which receives the alternating current from the cell P and carries the wedge W. An arrangement using two photoelectric cells in a bridge circuit is also described. Specifications 291,397, [Class 97 (i), Optical systems &c.], and 373,744 are referred to.