GB688648A - Improvements in or relating to spectrographs - Google Patents

Abstract

688,648. Photo - electric spectrograph. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 7, 1951 [June 16, 1950], No. 15065/50. Class 40 (iii). In a spectrograph in which a part of the spectrum is cyclically scanned by a light-sensitive device, means are provided for generating pulses synchronized with the scanning so as to select a particular spectral line for measurement. As shown in Fig. 2, the part of the spectrum under examination is formed in a narrow slit 14 with adjustable jaws 11, 12 and about one millimetre in width. Behind the jaws is rotated at constant speed by an air-driven motor a quartz drum 16. This drum is internally blackened but is provided with a series of slits 20 in the blackening about 20 microns wide and one centimetre in height through which light passes during the rotation of the drum. The light passing each slit is reflected horizontally by a mirror 22 and vertically by a further mirror 23 on to a photo-multiplier tube 27 (Fig. 1), incorporated in a head with an amplifier 32. An eyepiece 35 is incorporated provided with a graticule so that the multiplier tube may be removed and the eyepiece lowered so that the graticule occupies the position of the multiplier cathode thus facilitating focusing. At a point in the scan of the slit by each line on the drum, a neon tube is illuminated, its light being received by the multiplier tube. This tube developes a synchronizing signal which (1) triggers the time base of a cathode-ray tube; (2) extinguishes the neon tube until the next scanning cycle, and (3) initiates a strobing pulse at a point in the cycle which opens a gate to select part of the multiplier output derived from the spectrum. In a modification a single slit may be moved by a coil in a radial magnetic field, a further coil on the same shaft providing the synchronizing pulse. If the slit makes a simple harmonic motion a compensating circuit may be used. Circuits.-The output of the head amplifier 32 is fed to the upper pair of Y-plates of a double beam cathode-ray tube 19, to a synchronizing pulse separating circuit 48 and to gating circuits 49. The synchronizing pulse separating circuit 48 triggers a time base circuit 54 the output of which is fed to the X-plates of the cathode-ray tube, back to the pulse separator to paralyse the trigger circuit during the sweep and is used to extinguish the neon tube. The output of the pulse separator is also used to develop variable width rectangular strobing pulses which are then differentiated in a unit 47, and used to open gating circuits 49 at predetermined instants in the time base sweep so that the output of the photo-multiplier is passed to averaging circuits 52 when the selected part of the spectrum is being viewed. The strobe pulses are averaged in. a unit 50 and applied to the lower Y-deflection plates of the double beam cathoderay tube. Thus the strobing pulses appear beneath the waveform on the tube and the position of each strobing pulse along the tine base may then be adjusted. A number of strobing pulses may select different parts of the spectrum for simultaneous examination.