This invention relates, in general, to spectrochemical analysis of materials and is concerned especially with a spectrum line light rectifying method and apparatus for use with a spectrometer of the direct reading type, such as has been described in earlier patents, Nos. 2,577,814,-2,577,815 and 2,647,236. The term "light" as employed herein is intended to signify radiant energy of any wavelength appropriate for emission spectroscopy.
In a spectrometer of the direct reading type described in the noted patents, spectrum line light is measured photoelectrically to observe the presence of constituent elements in an electrically excited sample. In thus carrying out a spectrum analysis of a sample, spectrum lines produced from the excited sample are caused to pass between "knife edges" slightly spaced apart to define apertures commonly referred to as "exit slits." It is highly essential that each of the spectrum lines coincide and fall in true alignment with their respective exit slits in order that substantially all of the light intensity for any one of the lines may be Observed by a detector such as a photomultiplier tube, for example. Should a part of the light of any one of the lines become blocked out, as a result of that spectrum line impinging on one of the knife edges defining the exit slit, a serious inaccuracy will develop in the analysis. It is found that quite frequently the optical components of a spectrometer, when in use, may undergo slight changes in position and the spectrum lines then become partially blocked because of incorrectly centered positions in their respective exit slits This necessitates troublesome and timeconsuming adjustments of one or more of the optical components of the apparatus.
It is an object of the invention to provide an apparatus for rectifying the path of travel of spectrum line light which passes through exit slits and, generally, to improve spectrometers of the direct reading type. Specifically, it is an object to devise spectrum line light rectifying means which may be combined with standard spectrometer components to deal with the above-indicated problem of maintaining spectrum lines in centered relationship with respect to exit slits.
It is a further object of the invention to provide means for automatically aligning spectrum-lines with their exit slits so that delicate hand adjustments are eliminated. Still another object is to provide an automatic rectifying technique which, although not in effect during the interval when a metal sample is electrically excited may, however, be maintained constantly in operation at all other times.
We have determined that the foregoing objectives may be achieved in a highly accurate and rapid manner by making use of a differential light attenuating procedure. Essentially, this technique is based on the novel concept of passing spectrum line light through a differential light attenuating device and producing spectrum line light components which induce electrical signals of opposite phase and which signals vary in accordance with any change.
of position of optical elements in a direct reading type spectrometer. The electrical signals produced in this manner are combined with special electrochemical means for moving the spectrum line light and some related optical element so that balancing of light components and consequently electrical signals of opposite phase is accomplished, thus providing a continuous compensation for any unwanted change in position of optical elements and proper realignment of spectrum line light.
As one suitable means for causing spectrum line light to undergo differential light attenuation as noted, we have devised a special differential light attenuating structure which includes two separated apertures defined by two pairs of knife edges, located one above another so as to transmit two separate beams of light, and so arranged as to vary the ratio of intensity of light from the two beams as the position of the beams and their respective apertures are varied relative to one another.
The knife edge pairs are, in accordance with the invention, associated with the conventional exit slit structure of a spectrometer of direct reading type so that the knife edge pairs may receive. spectrum lines from the grating of the spectrometer and so that any misalignment between the standard exit slits and the other optical components of the spectrometer will also be present with respect to the knife edge pairs. Thus, a correction in positioning the two knife edge pairs will necessarily result in a correction of the associated exit slits.
Further details of construction of preferred embodiments of the invention selected for purposes of illustration are shown in the accompanying drawings, in which
Fig. 1 is an exploded perspective view illustrating one preferred embodiment of a spectrometer in which ismounted the rectifying device of the invention;
Fig. 2 is a detail plan view of a grating mount and grating element supported thereon as employed in the apparatus shown in Fig. 1;
Fig. 3 is a front elevational view of the structure shown in Fig. 2;
Fig. 4 is an enlarged perspective view of the spectrometer components with portions of the housing having been removed and indicating somewhat schematically electrical components connected to related elements of the spectrometer and particularly illustrating the rectifying apparatus of the invention mounted in an operation position;
Fig. 5 is an enlarged plan view showing the front portion of the structure illustrated in Fig. 4 and further illustrating the rectifying components of the invention mounted in association with conventional spectrometer structure;
Fig. 6 is a view in end elevation of the structure shown in Figs. 1, 4 and 5 further illustrating the rectifying components and the protective housing details of construction;
Fig. 7 is an electrical wiring diagram showing schematically the circuitry and some of the electrical components employed in carrying out the rectifying method of the invention;
Fig. 8 is another wiring diagram illustrating schematically a modified form of apparatus of the invention in which two photomultiplier tubes are employed;
Fig. 9 is a diagrammatic view illustrating another means of producing relative movement of spectrum lines by varying the position of a grating member;
Fig. 10 is a diagrammatic view similar to Fig. 9 but illustrating means for varying the relative position of spectrum lines by varying the position of a mirror to make the entrance slits appear to move;
Fig. 31 is a diagrammatic view similar to Figs. 9 and