GB790434A - Improvements in or relating to double beam spectrometers - Google Patents

Abstract

790,434. Photo-electric spectrometers. PARSONS & CO., Ltd., C. A. March 23, 1956 [April 13, 1955], No. 10607/55. Class 40 (3). In a double-beam spectrometer a chopping means alternately passes and blocks the radiation beams for substantially equal periods before they enter a monochromator whose associated output detector produces an electric signal which is amplified and applied to filter circuits selecting a signal at the chopping frequency and a signal at half that frequency, these signals being fed to comparison means. In the embodiment described, shutter D, apertured in 90 degrees arcs, as shown in Fig. 1b, is rotated in synchronism with the reciprocating motion of a pair of plane mirrors C driven as described in Specification 666,270. The electrical output of the radiation detector (see Fig. 3), is applied via high-gain amplifier 2 provided with filter circuits 3, 4, one selecting the component at the chopping frequency whose amplitude is proportional to the radiation energy A traversing the comparison cell plus that, B, traversing the sample and the other selecting the component, of amplitude proportional to (A - B), at half the chopping frequency, to conventional rectifying and smoothing circuits and thence via the arrangement shown of potentiometers 5, 6 to a self-balancing potentiometer whose pointer records the transmittance, B/A, of the sample.