GB1068884A - Spectrophotometer - Google Patents

Abstract

1,068,884. Photo-electric spectrophotometers. K. A. L. AKERMAN. May 14, 1964 [May 14, 1963], No. 20236/64. Heading G1A. [Also in Division G2] A spectrophotometer comprises a source of radiation, a mirror system directing a beam of radiation from the source alternately through a sample and a reference to an optical magnifier whence the radiation falls on a photo-multiplier and means for taking the logarithm of the photomultiplier response. The image of the aperture 7, illuminated by a monochromator 4, is reflected into a mirror system 9 including a mirror 11 oscillated angularly between two positions by an electromagnetic device 12 energized by a rectangular wave from a double voltage limiting diode 19. In the two positions light is reflected respectively to sample and reference points 13 in a microscope slide carrying a biological cell. These points may be selected rotating the mirror unit 9 and adjusting the oscillatory amplitude of mirror 11. Light from both points passes through the microscope 14, 15 to the cathode 17 of the photo-multiplier. A feedback circuit maintains the photo -multiplier current constant by altering the dynode potential. This potential includes a square wave component proportional to the difference in transmissivity between the sample and reference and, after operation in the logarithmic amplifier 18, the difference in extinction. This logarithm signal is analyzed by a phase sensitive rectifier comprising a transformer 31 with a centre tapped secondary and a switch 32 synchronized with the electromagnetic device 12. The duty cycle of the switch 32 is such that transients are avoided, and the output from the switch is connected via a filter 33,. 34 to a recorder 38. The paper drive of the recorder is coupled with a drive for the dispersion element of the monochromator 4.