Patent GB-968969-A (GB)
Title: Spectrophotometer
IPC: G01J3/06
Filed: 1963-02-26
Abstract: 968,969. Photo-electric spectrophotometers. BECKMAN INSTRUMENTS Inc. Feb. 26, 1963 [Feb.26, 1962], No. 7620/63. Heading G1A. In a spectrophotometer in which the sample is irradiated by a beam of radiation produced by a monochromator comprising a grating and means for separating the spectral orders produced by such grating the latter being driven cyclically by a wavelength drive means to cause the monochromator to scan through at least two spectra of adjacent order having at least one common wavelength, the movement of the record chart on which signals indicative of the optical properties of the sample are recorded and which is driven by means connected to the wavelength drive means is stopped when the common wavelength is produced by the monochromator in one spectral order and restarted when such common wavelength is produced in an adjacent order so that a continuous, uninterrupted record of the optical properties of the sample as a function of wavelength is produced. As described in connection with Figs. 1 and 2, the motion of the grating 30 is produced by a cam 12 and that of the means for separating the spectral orders, which may comprise a mirror or a filter control system, by a cam 14, both cams being carried by a shaft 16 which also carries a transparent disc 34 (of glass or plastic) and is driven via gears 42, 44 by means of a wavelength drive device 46 controlled by motor 70. The disc 34 is provided, inter-alia, with opaque areas 36, 38, 40 which, in co-operation with a radiation source (e.g. an incandescent lamp) 50-see Fig. 2, slit 54 and radiation detector (e.g. a cadmium selenide cell) 56, produce, on the interruption of the radiation path, an output signal from a trigger circuit 58 controlling a relay 60 the contacts 62, 64 of which are thereby opened. The angular position of the opaque areas 36, 38, 40 are so located relatively to cam 12 that the contacts 62, 64 are opened whenever the common wavelength is produced in one spectral order by the monochromator and are then, subsequently, closed on the production of the same wavelength in the next adjacent order. The opening of contact 62 interrupts the power supply to a magnetic clutch 68 which then decouples the drive between motor 70 and the mechanism 72 driving the recording chart 74 and the opening of contact 64 interrupts the circuit from the spectrophotometer radiation detects to the recorder pen servomotor 78. Recording of the optical properties of the sample thus stops at the common wavelength and is subsequently recommenced at this wavelength when the latter is produced by the monochromator in the next adjacent spectral order so that a continuous record free from interruptions is produced. The disc 34 is also provided with a series of wavelength graduations comprising translucent portions 49 in an opaque ring 48 which portions, in co-operation with a radiation source 90, slit 94 and radiation detector 96 (similar to elements 50, 54, 56), produce (when 96 is irradiated) an output signal from a trigger 98 controlling a relay 100 the switch arm 102 of which changes from contact 104 to contact 114 to produce a pulse by discharging a capacitor 110 (normally charged by battery 108 via resistor 112) through resistors 77 and 112. This pulse produces a momentary trace on chart 74 which forms a wavelength scale. A further wavelength scale is provided on the outer periphery of disc 34 and this is optically projected on to a viewing screen 41 by means of a light source 35. The grating cam 12 may have other than four lobes as shown and disc 34 may be generally opaque with the areas 36, 38, 40 transparent, trigger circuit 58 in this case being arranged to produce an output signal on the receipt of an input from the radiation detector 56. Also the ring 98 may be transparent and the bars 49 opaque. The radiation sources and the detectors may be positioned on the same side of the disc with the latter transparent and the areas and bars reflective, or vice-versa. If desired the optical control systems may be replaced by a magnetic system. Specification 864,981 is referred to.