GB719745A - Improvements in or relating to spectral scanning method and apparatus - Google Patents

Abstract

719,745. Photo-electric spectrometers. BECKMAN INSTRUMENTS, Inc. Aug. 13, 1952, No. 20349/52. Class 40 (3). [Also in Group XXXVIII] In a recording spectrometer of the type in which a spectrum is traversed relatively to a slit behind which is situated a sensitive device and in which the width of the slit is adjustable, the rate of traverse of the spectrum is made proportional to the slit width and inversely proportional to the response period of the recording. system. As shown, slit width shaft 55 is adjusted bv a servo motor 61 fed from a signal source 64 through amplifiers 63, 62 according to a prearranged "programme" While adjusting slit width servo motor 61 also adjusts a tapping of a potentiometer 65. The voltage developed between the potentiometer tapping and earth is "backedoff by a voltage developed by a D.C. generator 69 driven by the wave'length. adjusting motor 70, which may rock the spectrometer prism or a wavelength selecting mirror. The difference in voltage between the potentiometer tapping and the D.C. generator output feeds a servo-amplifier 71 driving the wavelength motor which rotates at a speed sufficient to keep the two voltages equal. Thus the spectrum is displaced at a rate proportional to slit width. So as to make the wavelength adjustment, inversely proportional to the response period of the mechanism a tapping on a further potentiometer 67 is adjusted in accordance with this period. This potentiometer is series connected with potentiometer 66 and changes the range of speeds over which the slit width control operates. In a modification (Fig. 4) the spectrometer is of the type in which wavelength adjustments are made in a series of steps. In this embodiment the slit width motor 75 moves a contact over a stepped potentiometer 80. The voltage developed is backed off by that developed between earth and tapping 82 driven by the wavelength motor 83 of second potentiometer. Both voltages are applied to a discriminator 88 which applies the unbalance signal to a servoamplifier 90. The amplified signal energizes the wavelength motor 83 which drives contact 82 upwards from a rest positions until balance is attained. A sequence controller 91 responds to the zero signal in amplifier 90 and de-energizes a clutch actuator 92 to open clutches 84, 85. Contact 82 is returned by a spring and the sequence controller 91 switches the instrument to the next balancing cycle. Thus the spectrum is intermittently displaced by movements proportional to the slit width. The response time of the measuring system is taken into account by the "dwell time" of the wavelength motor between each balancing cycle.