Spectrometric measuring device

Abstract

The present disclosure includes a spectrometric measuring device for a measurement point of the process automation system, including a broadband light source for radiating light through an entrance aperture onto a sample to be measured, wherein the beam bundles of the light form an irradiation plane, a light limiter that limits the light at an angle to the irradiation plane, whereby a different amount of light results at this angle. The device further includes a dispersive element for separating the light according to its wavelength and a detector for receiving light separated according to its wavelength, wherein the light source beams the light through the sample to the entrance aperture, the light limiter and the dispersive element, and the light strikes the detector.

Claims

1. A spectrometric measuring device for a measurement point of a process automation system, the device comprising: a broadband light source configured to emit a beam of light along a light path through a sample to be measured and through an entrance aperture, wherein the beam of the light defines an irradiation plane in an X-Y plane; a spatial filter disposed along the light path, the spatial filter configured to limit the beam an amount that varies along the Z-axis; a prism, mirror or grating configured to separate the light into its wavelengths; and a detector adapted to receive the light separated into its wavelengths by the prism, mirror or grating, wherein the detector is a two-dimensional detector, wherein the light source emits the beam of light through the sample, the entrance aperture, the spatial filter and the prism, mirror or grating, and the light is subsequently incident upon the detector, wherein the spatial filter is structured such that a blurred shadow is generated on the X-Y detector area and thereby a varying amount of light on the detector as a function of the Z-coordinate.

2. The spectrometric measuring device of claim 1, wherein the entrance aperture includes the spatial filter.

3. The spectrometric measuring device of claim 2, wherein the spatial filter is conical.

4. The spectrometric measuring device of claim 2, wherein the spatial filter is step-like.

5. The spectrometric measuring device of claim 1, wherein the spatial filter is disposed between light source and the prism, mirror or grating.

6. The spectrometric measuring device of claim 1, wherein the angle to the irradiation plane is approximately 90.

7. The spectrometric measuring device of claim 1, further comprising at least one imaging system for directing the light from the light source in a direction of the prism, mirror or grating and/or from the prism, mirror or grating in a direction of the detector.

8. The spectrometric measuring device of claim 7, wherein the at least one imaging system includes a concave mirror.

9. The spectrometric measuring device of claim 7, wherein the spatial filter is disposed between the light source and an imaging system, and wherein the imaging system directs the light from the light source to the prism, mirror or grating.

10. The spectrometric measuring device of claim 1, wherein the spatial filter is a diaphragm.

11. The spectrometric measuring device of claim 10, wherein the diaphragm has a comb-like form.

12. The spectrometric measuring device of claim 1, wherein the spatial filter is configured such that the light at the angle to the irradiation plane is attenuated such that, at the angle, a different amount of light continuously results.

13. The spectrometric measuring device of claim 1, wherein the light path includes a measurement path and a reference path, wherein separate portions light from the light source are directed via the measurement path and the reference path, wherein the reference path does not pass through the sample.

14. The spectrometric measuring device of claim 13, wherein the light of the reference path, which passes through the spatial filter at the angle to the irradiation plane is spatially separated from the light of the measurement path on the detector.

15. The spectrometric measuring device of claim 13, wherein the entrance aperture includes the spatial filter, and the light of the reference path is coupled to the spatial filter via an optical fiber.

16. The spectrometric measuring device of claim 13, wherein, to compensate for light intensity fluctuations of the light source, the spatially separately light intensities of the reference path at the detector are linked via a mathematical process with the light intensities of the measurement path.

17. The spectrometric measuring device of claim 16, wherein the mathematical process linking the light intensities of the reference path and the measurement path is a division.

18. The spectrometric measuring device of claim 1, further comprising collimating optics configured to image light only from a spatially limited area of the light source onto the detector.

19. The spectrometric measuring device of claim 18, wherein the collimating optics are configured to image light from a center of the light source onto the detector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure is explained in more detail with reference to the following figures, which include:

(2) FIG. 1 shows a optical absorption spectrometer, according to the present disclosure;

(3) FIG. 2 shows an embodiment of a light limiter;

(4) FIG. 3 shows an image resulting from the light limiter of FIG. 2 on a detector;

(5) FIG. 4 shows another embodiment of a light limiter, according to the present disclosure;

(6) FIG. 5 shows an embodiment of an optical absorption spectrometer, according to the present disclosure;

(7) FIGS. 6A-6C show embodiments of a light limiter applicable to the spectrometer of FIG. 5;

(8) FIG. 7 shows an embodiment of an absorption spectrometer with reference path;

(9) FIG. 8 shows another embodiment of the absorption spectrometer with reference path;

(10) FIG. 9 shows an embodiment of the light limiter applicable to the embodiments of FIGS. 7 and 8; and

(11) FIG. 10 shows an image resulting from the light limiter of FIG. 9 on a detector.

(12) In the figures, the same features are identified with the same reference symbols. In the following, the right-left axis shall be designated as the x-axis, the top-bottom axis as the y-axis, and the axis from the plane as the z-axis.

DETAILED DESCRIPTION

(13) A spectrometric measurement system according to the present disclosure is mark identified with the reference symbol 1 and is shown in FIG. 1.

(14) The spectrometer 1 may be an absorption spectrometer including a broadband light source 2, e.g., a pulsed flash lamp, a detector 3, an entrance aperture 7, and a dispersive element 4. The dispersive element 4 may be an optical grating, for example, a reflective grating. In other embodiments the dispersive element 4 may be, for instance, a prism, special mirrors or transmission grating.

(15) The light from the light source 2 is parallelized (collimated), for example, by means of a lens 10 and radiated through a sample 9. As a result of the collimation, a spatial selection of the light is enabled such that, for example, only light components from the spatial center of the light source 2 are radiated through the sample 9. One advantage that may result from the spatial selection of the light is that a selection of the light occurs from areas in the light source 2 that have a particularly low pulse-to-pulse fluctuation between individual flashes. To this end, additional pinhole diaphragms (e.g., which block out the light from peripheral regions of the light source), if applicable, or other optical devices known from prior art are used.

(16) A lens 11 directs the light onto the entrance aperture 7 of the spectrometer 1 used for detection. As an alternative to the use of a single lens 11, a lens system, optical fiber, mirror system, or the like may be used.

(17) The absorption spectrometer 1 shown includes the entrance aperture 7, a light limiter 5, and a first imaging system 8a for transmitting a beam bundle 6 from the entrance aperture 7 to the dispersive element 4. The spectrometer 1 includes a second imaging system 8b for transmitting the beam bundle 6 from the dispersive element 4 to the detector 3. In the beam path of the beam bundle 6 between dispersive element 4 and detector 3 conventional optical components may be integrated, such as a deflecting mirror or optical order-sorting filter for blocking out signals of higher orders of diffraction. The first and second imaging systems 8a, 8b are realized approximately above concave mirrors.

(18) The light from the light source 2 is radiated through an entrance aperture 7 in the direction of the first imaging system 8a. The entrance aperture 7 is oriented along a z-axis. The light forms undle the beam b6, which is defined by a left light beam 2.1 and a right light beam 2.r. The light beams 2.1 and 2.r span an irradiation plane, which corresponds to an x-y plane (orthongonal to the z-axis) or is parallel thereto.

(19) If the entrance aperture 7 is illuminated with a spectrum (e.g., broadband light source 2), lines in the form of the aperture are also obtained on a detector plane on the x-z-axis, spectrally separated, however.

(20) The detector 3 may be a two-dimensional (2-D) detector. In such an embodiment, the detector 3 is a detector array, oriented on the x-y-axis. At the same time, the spectrometer 1 may be configured such that different signal amplitudes are on different z-coordinates of the detector 3, but have the same spectral characteristic. In one embodiment, the detector 3 is tilted with respect to the x-z-axis, for example, with respect to the x-axis.

(21) To this end, the light limiter 5 is arranged between the light source 2 and the sample 9 and, thereby the detector 3 as well. The light limiter 5 limits the light of the light source 2 at an angle, e.g., approximately 90, to the irradiation plane, i.e., the x-y plane. In such an embodiment, the light limiter 5 limits the light on the z-axis. There thus results a different amount of light on the z-axis, which ultimately is incident on the detector 3. The light limiter 5 may have an asymmetrical configuration. In such an embodiment, the light limiter 5 varies in width or thickness along, for example, its longest edge.

(22) The entrance aperture 7 may be approximately an entrance slit, for example, an entrance slit 7. In at least one embodiment, the entrance aperture 7 is not symmetrical, for example, as light limiter 5. If the entrance aperture 7 is enlarged, more light is generally incident upon the detector 3, however, at the cost of the spectral resolution being lower. If the entrance aperture 7 is conical, as shown in FIG. 2, i.e., on the x-z plane, (white area transmits light), the image in FIG. 3 results on the x-z detector plane, with (as an example) three sharp frequency lines. The reference symbol B corresponds to blue light, reference symbol G to yellow light, and reference symbol R to red light. The sign of the z-axis is thereby mirrored, if applicable. The decisive factor is that only a very low signal amplitude is available in the areas on the z-plane with a small slit, but a greater signal is available in the areas with a large slit for the entrance aperture 7.

(23) This effect can be taken advantage because signal information is taken from the detector plane from different z-coordinates, depending upon the intensity and wavelength. The intensity of the measurement signal is inferred for each wavelength from that line (z-coordinate) that is optimally controlled in detector 3. Accordingly, the dynamic range of the photodetector 3, e.g., a CCD, can be drastically increased. This mechanism may be used both for continuous light sources 2, such as halogen lamps, and for pulsed flash lamps.

(24) FIG. 4 shows an embodiment of the light limiter 5 in which the light limiter has a step-like design.

(25) In an embodiment, as shown in FIG. 5, the light limiter 5 is disposed on the z-axis in proximity of the first imaging system 8a, which may be a concave mirror. Shown in FIG. 5 is an embodiment in which the light limiter 5 is arranged at approximately of the distance between entrance aperture 7 and the first imaging system 8a. The light limiter 5 is a spatial diaphragm, which causes a blurred shadow to be cast on the detector 3 along the z-axis.

(26) At the same time, the diaphragm, i.e., the light limiter 5, in relation to the entrance aperture 7 may have on the x-z plane a form as shown in FIGS. 6A, 6B and 6C, in which the form of the entrance aperture 7 on the x-z plane is outlined in black. A continuous gray filter may also be used here. The advantage of the structures shown in FIG. 6B and FIG. 6C is that, here, due to the blurred image, a continuous intensity curve in the z-direction may be achieved through a black/white diaphragm, as may be realized, for example, by a structured blackened plate. Such a blackened structure may be realized more simply and more cost-effectively as a continuous gray filter. In all embodiments, the light limiter 5 is structured such that a blurred shadow is generated on the x-y detector area and thereby a changing, varying amount of light on the detector 3 as a function of the z-coordinate.

(27) The photodetector 3 may thus be controlled such that pixels of the detector 3 in the maximally-shaded area on the wavelength with maximum detector amplitude are not overexcited. For wavelengths with less signal, the measurand for pixels with a z-coordinate is determined, for which less shadow is effective. Advantageously, a read-out direction is selected such that the lines (z-axis) with a low signal level in the detector are read out first, and the lines with a high signal level thereafter.

(28) FIG. 7 shows an embodiment of the absorption spectrometer 1 with a measurement path ME and a reference path RE of the light. The measurement path ME is the one described herein in relation to, for example, FIG. 1. The reference path RE is a light path that is not directed through the sample 9. Instead, the reference path RE is directed around and past the sample 9. Downstream of the sample 9, the path is directed through the entrance aperture 7. The descriptions relating to FIG. 1 and FIG. 5 are applicable. If applicable, a different embodiment of the light limiter 5 results; see, in this regard, below and FIG. 9.

(29) In the embodiment shown in FIG. 7, the spectrometer 1 includes several deflectors 11 disposed in the reference path RE, which form a deflector system. In such an embodiment, light from the light source 2 is directed around the sample 9 with several deflectors 11, which may be, for instance, mirrors or semi-transparent mirrors. In an embodiment, the deflectors 11 that are arranged closest to the light source 2 and to the entrance aperture 7 may each be semi-transparent mirrors. In one embodiment, the deflectors 11 that are arranged closest to the light source 2 and to the entrance aperture 7 are configured as tilting mirrors. Depending upon whether the measuring path ME or the reference path RE is to be measured, the each tilting mirror, i.e., the deflectors 11, is shifted accordingly. Each tilting mirror may have either a monostable or bistable design. Each tilting mirror may be controlled by means of an electric motor or magnetically. An advantage of the embodiment having semi-transparent mirrors is that a reference measurement (simultaneously with a sample measurement) may be performed continuously, such that pulse-to-pulse fluctuations of a pulse-controlled light source 2 may, for instance, also be compensated for.

(30) In the embodiment shown in FIG. 8, the spectrometer 1 includes a fiber optic cable 12 arranged in the reference path RE fiber optic cable 12 receives light from the light source 2 and transmits the light around the sample 9. Downstream of the sample 9, the light from the fiber optic cable 12 is coupled again, i.e., directed through the entrance aperture 7. If applicable, a beam splitter, semi-transparent mirror, or a tilting mirror may be arranged downstream of the light source 2 to switch between the reference path RE and the measuring path ME.

(31) FIG. 9 shows an embodiment of the light limiter 5, which is suitable, in particular, for the spectrometers 1 of FIGS. 7 and 8. In such an embodiment, the light limiter 5 includes two zones 5.1 and 5.2. The first zone 5.1 corresponds essentially to the embodiment of FIG. 2 or FIG. 4. The second zone 5.2 is additional to the first zone 5.1. The second zone 5.2 may have the form of a circle as shown; however, other forms such as square, rectangle, etc., are possible. A triangular or stepped structure, as in the first zone 5.1, is also possible for the second zone 5.2. The light limiter 5 with the two zones 5.1, 5.2 is arranged such that light from the reference path RE is always radiated through the second zone 5.2, and the first zone 5.1 has light radiated along the measuring path ME. In such an embodiment, the image in FIG. 10 results on the detector 3. As shown, the light from the reference path RE arrives at the same place on the detector 3 and is, in particular, spatially separated from the light from the measuring path ME. When a two-dimensional image is received on the detector 3, the intensity of the reference path RE and of the measuring path ME can thus be detected simultaneously for each light pulse in each case. Pulse-to-pulse fluctuations in the intensity of the light source may thus be compensated for mathematically.