GB869257A - Spectroscopic apparatus - Google Patents

Abstract

869,257. Spectroscopic apparatus. BAIRDATOMIC Inc. Oct. 30, 1957, No. 33823/57. Class 40(3) [Also in Groups XX and XXXV] Spectroscopic apparatus in which changes in the spatial relationship between the various components due to variation in ambient temperature are compensated by the reorientation of the light dispersal member in response to a received monitor radiation. Light from the sample 24, Fig. 1, under test passes through a lens 34 and slit 36 and is reflected by a mirror 38 to a dispersal member 40 comprising a curved diffraction grating. Preselected portions of the resulting spectrum pass through slits 42 and are reflected by mirrors 44 to the photo-multipliers 46. A twin beam of monitor radiation, each beam alternately radiating at mains frequency, is generated by a lamp 50 and pasess via lens 52 and slit 54 to the diffraction grating 40. The beams are directed by the grating to the offset slits 56 and 58 and hence via the mirror 60 to the photo-multiplier 62. The apparatus is initially adjusted to allow equal amounts of light to enter each slit thus generating in the photo-multiplier an equal voltage during each half cycle of mains frequency. Any change in spatial relationships causes the beams to deviate from their set position and produces an unbalance in the photo-multiplier output voltage. This voltage is applied via the transformer 144, Fig. 5, to the amplifying valves 146, 148, 150 and 152 and the output of valves 152 is applied to the winding 160 of the transformer 154. The centre tap of this winding is connected to one winding of a split phase servomotor 102 having a second winding 168 which is connected to the mains supply via a condenser 170. When the monitor radiation to each slit is equal the screwed shaft 112 of the motor 102 is subjected to equal and opposite torques each half cycle and remains stationary. However, when inequality arises the motor shaft is turned and alters the position of a screwed block 114 which is coupled via a spring 116 to the bar 82 attached to the grating mount 40. Movement of the bar reorients the mount to rebalance the light incident on the slits 56 and 58 hence ensuring that the dispersed bands of light produced by the specimen are maintained incident on their respective wavelength slits.