DIFFRACTION GRATING SPECTROPHOTOMETER

1,093,294. Spectrophotometers. SHIMADZU SEISAKUSHO Ltd. June 15, 1966 [June 15, 1965], No. 26699/66. Heading G2J. [Also in Division G1] A spectrophotometer, having a radiation source, an entrance slit 24, a collimator 25 and two diffraction gratings G1, G2 rotatable about their own axes so as to form partly overlapping ranges of wavelengths, is provided with a mirror M which is movable into or out of a beam of light from the collimator 25 for selectively directing the beam towards each grating, movement of the mirror being effected when the two gratings G1, G2 are arranged to produce the same wavelength within the overlapping portion of the respective wavelength ranges. In the embodiment shown each grating is mounted on a shaft 32, 33 which also carries a lever L1, L2. The levers L1, L2 are urged against cams C1, C2 respectively. The cams C1, C2, together with further cams C3, C4, C5, are fixedly mounted on a shaft 34, driven by a motor 35. The third cam C3 actuates a micro-switch 41 to start a motor 40. The mirror M is moved by a belt 42 which is driven by the motor 40, an actuator 43 fixed to the belt being provided to actuate one of two microswitches 44a, 44b and so stop the mirror M. Light diffracted by the gratings returns to the collimator 25 and is then directed through a slit 27 on to a detector 31. Any unwanted frequencies of the diffracted light passing through the slit 27 are removed by the location in the light path of one of a selection of interferences filters F1, F2, F3, F4 mounted in a rotatable disc 45. A motor 46 rotates the disc 45 on actuation of one of two micro-switches 47, 48 by the co-operating cams C4, C5 respectively. Further micro-switches 49-52 are actuated by a projection 53 on the disc 45 in order to stop the motor 46. The cams C1-C5 are shaped so as to produce the required sequence of movements on actuation of the motor 35. With the mirror located in the light beam as shown, rotation of the cam C1 causes the grating G1 to scan a first wavelength range # 1 to # 2 . Cams C1 and C2 then cause the gratings G1, G2 to scan simultaneously an overlapping range # 2 to # 3 . During this operation the cam C3 operates the motor 40 to move the mirror out of the light path. Thereafter the grating G2 scans a further wavelength As to # 4 . The cams C4, C5 serve to change the filters F1-F4 as required.