Method for calibrating a spectrometric measuring device and spectrometric calibration device for carrying out the method

Abstract

The invention relates to a method for calibrating a spectrometric measuring device (20) using a spectrometric calibration device (01). The calibration device (01) comprises a control unit, an interferometer with mirrors (02, 03) and a beam splitter (04), a broadband first radiation source (06), a laser (07) as a second radiation source, and a first detector (08). The method includes emitting broadband radiation (12a) and simultaneously emitting radiation (12b) by the laser (07), as well as simultaneously coupling these two radiations (12a, 12b) into the interferometer of the calibration device. A first interferogram is acquired based on the radiation (12b) of the laser (07). A second interferogram is acquired based on the broadband radiation (12a). A first data set with the spectral properties of the spectrometric measuring device (20) is created on the basis of the recorded interferograms.A second dataset, consisting of high-resolution sample spectra and chemically determined constituent values, is provided. Simulated sample spectra are calculated from the two datasets. A chemometric calibration model for the measuring device (20) is created from the simulated sample spectra. The invention also relates to a spectrometric calibration device (01).

Description

[0001] The present invention relates to a method for calibrating a spectrometric measuring device. The invention further relates to a spectrometric calibration device suitable for carrying out this method.

[0002] The measuring device in question is particularly suitable for spectrometric ingredient analysis to determine the organic and / or inorganic ingredient concentrations of a sample, especially a bulk material. Ingredient analysis is particularly applicable in agriculture and the food industry. To achieve high accuracy in such analyses, the measuring device must be appropriately calibrated.

[0003] For ingredient analysis, the spectrometric measuring device (hereinafter also referred to as a spectrometer) records spectral measurements of the sample, which are influenced by the sample's constituents. By applying a chemometric model, the concentration of at least one ingredient being analyzed is deduced from the spectral measurements. The result is a value for the concentration of at least one ingredient in the sample. Chemometric methods are used for data analysis with the aid of algorithms. It is known to those skilled in the art from a subfield of chemometrics that spectra can be evaluated using mathematical-statistical methods, for example, using multivariate regression. Such methods can be used for the chemometric calibration of, for example, a spectrometer. Recorded spectra are subsequently also referred to as spectral measurements.

[0004] It is common practice to equip spectrometric measuring devices with line sensors and to perform wavelength calibration using a few, highly accurate known spectral lines from low-pressure lamps. A grating spectrometer with a line sensor is most often used, for example, a silicon-based spectrometer operating in the ultraviolet (UV) or visible (VIS) range, or an InGaAs-based spectrometer operating in the infrared range. Alternatively, filter-based spectrometers can be used, which are typically spectrally calibrated with monochromators. Various calibration methods involving the evaluation of specific wavelengths and / or scattered light are known.

[0005] Industrially manufactured spectrometers of the same series exhibit significant production variations. Until now, producing numerous spectrometers of the same series with as similar spectral properties as possible has been a challenging approach, allowing the exchange of the sometimes complex chemometric calibration models between individual instruments. However, the peak wavelength and / or the spectral bandwidth of the spectral channels typically vary considerably more than 0.2 nm between individual instruments due to manufacturing variations. This means that identical properties can no longer be assumed, and chemometric calibration models created once cannot be readily applied to multiple instruments of the same series. This problem is particularly prevalent in spectrometers with interference filters, especially polymer-based interference filters produced by vapor deposition.

[0006] Since it is practically impossible to equip all spectrometers of a series with sufficiently similar spectral properties, regular correction measurements with real samples on the individual instruments are necessary to adapt the chemometric models to each instrument. This is time-consuming and expensive, as numerous sample measurements must be performed with each individual spectrometer.

[0007] Therefore, a calibration procedure is desirable that eliminates the need to vary chemometric models to make them available for other spectrometers of the same design, as this procedure usually requires additional sample measurements and is associated with losses in the accuracy of the ingredient analysis.

[0008] A problem of spectrometric calibration is addressed in WO 2023 / 066 896 A1. According to this document, for spectrographic methods to be successful, the spectrographic instruments must perform reliably with negligible variations, particularly when comparing measurements from different spectrographic instruments. Specifically, the spectral data for a given sample should be at least similar or identical for different spectrographic instruments of the same type. WO 2023 / 066 896 A1 proposes a calibration procedure for a spectrometric device to solve this problem. The device comprises at least one detector unit, at least one optical element for splitting a light beam into wavelength components, and several photosensitive elements for detecting the wavelength components and generating a detector signal from them.The light beam is generated by means of at least one broadband light source. The light beam illuminates the spectrometric device, with the radiation passing through at least one interferometer. The detector unit generates a detector signal from the light beam. A further step of the process involves determining calibration information. However, the known calibration method is not precise enough to perform a fast, inexpensive, and accurate calibration for devices with significantly different properties. WO 2023 / 066 896 A1 does not address the creation of chemometric calibrations or chemometric models.

[0009] German patent application DE 10 2014 226 487 A1 describes an FTIR spectrometer comprising an interferometer, a reference laser source, and a scanning detector for determining the path difference of the interferometer. The scanning detector detects light from the reference laser source that has passed through the interferometer. The laser wavelength of the reference laser source is tunable within a tuning range. A portion of the light emitted from the reference laser source is directed through an absorption medium onto a reference detector. Within the tuning range of the reference laser source, the absorption medium exhibits an absorption line. Electronics allow the laser wavelength to be adjusted to the absorption line of the absorption medium by means of a signal from the reference detector. This is intended to achieve improved stabilization of the laser wavelength of the reference laser.

[0010] US Patent 2023 / 0304860A1 discloses a spectral modeling system for creating chemometric calibration models for spectral instruments. The approach described therein aims to create and use a unified chemometric calibration model for a variety of similar spectral instruments. The spectral modeling system described includes a spectral converter. The spectral converter is used to generate a variety of artificial spectra using spectral data from a variety of samples measured by a subset of a variety of spectral instruments, as well as spectral instrument properties that represent spectral variations in the variety of spectral instruments. The spectral modeling system also includes a machine for generating a unified chemometric model for one or more parameters associated with the variety of samples, based on the spectral data and the variety of artificial spectra.

[0011] An object of the present invention is to provide an improved method for calibrating a spectrometric measuring device, with which each individual spectrometric measuring device of a series can be calibrated with a high spectral absolute accuracy of 0.2 nm or better, in order to achieve satisfactory accuracy in the chemometric determination of the constituents of samples with the calibrated measuring device. Furthermore, it is an object of the present invention to provide a spectrometric calibration device that can perform such a method for calibrating a spectrometric measuring device.

[0012] These problems are solved by a method according to the invention as set forth in claim 1 and by a spectrometric calibration device as set forth in dependent claim 7.

[0013] The method according to the invention serves to calibrate a spectrometric measuring device using a spectrometric calibration device.

[0014] First, it should be clarified that the term "calibration" is used in two contexts below. If the calibration refers to the optical properties of a spectrometric measuring device, it is referred to as "spectral calibration." If the calibration refers to the creation of a chemometric model, it is referred to as "chemometric calibration," which is also frequently called a "beta vector." Both types of calibration are necessary components of improved ingredient analysis using the measuring device calibrated according to the invention.

[0015] The spectrometric calibration device preferably used for carrying out the method is an FTIR spectrometer. An FTIR spectrometer (Fourier-transform infrared spectrometer) is a special type of spectrometer in which the spectrum is not recorded by stepwise changes in wavelength, but is calculated by a Fourier transform of a measured interferogram.

[0016] The spectrometric measuring device to be calibrated can be, for example, a grating spectrometer or a filter-based spectrometer.

[0017] The spectrometric calibration device according to the invention, which can be used for calibrating the spectrometric measuring device, comprises a control unit, a beam splitter, and an interferometer with mirrors. In the spectrometric calibration device, a first mirror is movable and a second mirror is stationary, i.e., fixed with respect to the overall arrangement or the housing. Furthermore, the spectrometric calibration device comprises two radiation sources and a measuring unit with at least one detector. The first radiation source is a broadband radiation source, and the second radiation source is a reference laser (hereinafter also referred to simply as the laser). The broadband radiation source can be a halogen lamp. Alternative broadband radiation sources are, for example, LEDs, SLDs, arc lamps, or supercontinuum sources.The broadband radiation source covers at least the wavelength range used by the spectrometric measuring device to be calibrated in its operating mode. Preferably, a HeNe laser is used. The wavelength of the laser is thus precisely known for carrying out the method according to the invention. In particular, the wavelength of the laser should be known with an accuracy of at least 0.01 nm and be very stable over time. Preferably, the laser is stabilized with respect to both wavelength and intensity, the technical means for which are known to those skilled in the art and do not need to be described in detail here.

[0018] The inventive method for calibrating a spectrometric measuring device then comprises the following process steps: In the first step of the process, the broadband radiation source is caused to emit broadband electromagnetic radiation. Simultaneously, the laser emits electromagnetic radiation with a precisely known wavelength. The broadband radiation source and the laser are positioned so that they emit in the same beam path, allowing the two different electromagnetic radiations to simultaneously enter the interferometer of the spectrometric calibration unit, which is located at a distance from the two radiation sources in the beam path. Because the two radiation sources emit simultaneously, and thus the resulting optical effects can be evaluated at the same time, the overall measurement time required for the calibration process can be significantly reduced. Additionally, the usable luminous efficacy is increased.

[0019] According to a first embodiment, the radiation from the radiation sources is guided entirely in a free beam. Alternatively, the radiation from the radiation sources is guided partially in a free beam. According to a second embodiment, the radiation from the radiation sources is guided entirely in optical fibers. Alternatively, the radiation from the radiation sources is guided partially in optical fibers. Alternatively, preferably, the radiation from the radiation sources is guided entirely in photonic integrated circuits (PICs). Alternatively, the radiation from the radiation sources is guided partially in photonic integrated circuits (PICs).

[0020] Preferably, the radiation from the broadband radiation source is supplied to the spectrometric measuring device via a separate measuring head, which is connected to the calibration device via an optical fiber. The measuring head preferably contains components that modify the angular spectrum, for example, lenses, diffusers, or microlens arrays.

[0021] In a further process step, the two electromagnetic radiations are coupled into the interferometer of the calibration device, wherein the electromagnetic radiations are each split at the beam splitter into a first beam and a second beam, wherein each first beam is directed to the stationary mirror of the interferometer and is reflected back to the beam splitter at this mirror, and wherein each second beam passes through or through the beam splitter and is reflected back to the beam splitter at the movable mirror of the interferometer.

[0022] The beams reflected back onto the beam splitter (originally emitted by both radiation sources) exit the beam splitter as recombined radiation. The first beams pass through the beam splitter, while the second beams are reflected at the beam splitter. The recombined radiation is then directed to the measuring unit with detector.

[0023] In a further process step, a first interferogram is measured with the detector. Due to the complex superposition of the recombined radiation in the area of ​​the measuring unit, interference effects occur. The interfering, recombined radiation of the laser is preferably directed to a photodiode, which acts as a detector and is sensitive to the laser radiation wavelength.

[0024] In a further process step, based on the radiation from the broadband radiation source, the spectrometric measuring device measures further interferograms synchronously with the acquisition of the first laser interferogram. The spectrometric measuring device, which is being calibrated, serves as a detector for the interfering, recombined radiation from the broadband radiation source, with the interfering radiation from the broadband radiation source being directed to the spectrometric measuring device. Thus, during the calibration process, the spectrometric measuring device is a temporary component of the spectrometric calibration device and temporarily forms the spectrally resolving detector for the broadband radiation.

[0025] The spectrometric calibration device (FTIR spectrometer) preferably comprises a measuring head connected to the spectrometric measuring device to be calibrated via an optical fiber. The measuring head preferably includes an optical diffuser and other optical elements as well as spectral selection elements, which, using the lamp illumination, reproduce the angular spectrum of a reflective sample as closely as possible. This is advantageous because the angular spectrum of the detector illumination influences the spectral detection characteristics of the spectrometric measuring device.

[0026] Since both radiation sources are coupled into the spectrometric calibration device simultaneously and their interfering radiation is detected concurrently, the laser radiation experiences the same phase disturbances as the broadband radiation. This makes it possible to use the laser interferogram to computationally eliminate the phase disturbances in the interferogram of the broadband radiation (lamp interferogram). It is crucial that the intensity measurements with the photodiode, as the detector of the electromagnetic radiation emitted by the laser, and with the spectrometric measuring device being calibrated, as the temporary detector of the broadband electromagnetic radiation emitted by the lamp, are performed synchronously.

[0027] To generate the interferograms, the position of the movable mirror must be changed. For this purpose, the spectrometric calibration device preferably includes a mirror adjustment device. The interferograms are acquired by setting the movable mirror to equidistant or non-equidistant positions. A useful advantage of the method according to the invention in this context is that the spectrometric calibration device compensates for positioning errors of the mirror adjustment device when the latter is operated stepwise.

[0028] Alternatively, the spectrometric calibration device can be operated with a continuous (periodic) movement of the mirror adjustment device. In this case as well, the laser interference signal can be used to detect the mirror movement with high accuracy and to serve as a correction signal during spectrometric calibration.

[0029] The mirrors can preferably be formed by retroreflectors. In particular, the mirror can be an angle-mistake-compensating retroreflector (corner cubes). Preferably, the beams from the two radiation sources are superimposed collinearly so that they always pass through the same volumes of air. Optical components arranged in the beam path are used for the superposition, preferably dichroic beam splitters. Due to the superposition, both beam paths experience similar phase changes due to spatial fluctuations (vibrations) and / or temperature changes and / or fluctuations in the air's refractive index.

[0030] Alternatively, the beams from the two radiation sources are superimposed concentrically, with one radiation source predominantly utilizing an inner region with a smaller beam diameter and the other radiation source predominantly an outer region with a larger beam diameter. In this embodiment, the superposition of the beams is preferably achieved by using mirrors with a hole for coupling in and out. One of the beams, preferably the laser radiation, is coupled into the spectrometric calibration device (FTIR spectrometer) through the hole of a first mirror and coupled out again through the hole of a second mirror. The coupling in and out of the broadband lamp radiation is achieved by reflection at the mirrors. Alternatively, the lamp radiation can be guided through the holes and the laser radiation reflected.

[0031] The laser provides a highly accurate, known reference wavelength measurement with each measurement, thereby achieving improved absolute wavelength accuracy during the spectral calibration of the spectral measuring device. The optical path difference (OPD) can be determined using the laser's reference wavelength measurement.

[0032] In a further process step, an initial dataset is created, containing the spectral properties of the spectrometric measuring device based on the acquired interferograms. A second dataset is then provided, consisting of precise, high-resolution sample spectra and corresponding, chemically determined constituent values. Simulated sample spectra are then calculated from these two datasets.

[0033] The chemometric calibration model is created in a further process step using simulated (synthetically calculated) sample spectra, so that no physical (organic) samples need to be remeasured for individual spectrometric measuring devices (single spectrometers). Preferably, a PLS calibration (partial least squares regression) is used to create the chemometric calibration model. A machine learning system can preferably be used to create the chemometric calibration model.

[0034] To generate the simulated sample spectra, the aforementioned at least two datasets are used. The first dataset comprises the spectral properties of the single spectrometer, which will later be used for ingredient measurements. The second dataset includes high-resolution sample spectra with high wavelength accuracy, as well as the corresponding ingredient concentrations. The optical spectra of the second dataset should be so precise that they can be considered spectrometrically correct, as they form the basis for the simulation of the synthetic sample spectra, which serve to create chemometric calibration models for the spectroscopic measuring device. Generating such datasets is a complex process. The second dataset can, for example, be extracted from existing databases.Alternatively, it can be acquired with a precise, high-resolution master spectrometer, which can also be calibrated with the spectrometric calibration device. The master spectrometer typically has a higher spectral resolution than the spectrometric measuring device. The absolute spectral accuracy of these sample spectra should be in the range of ±0.2 nm or better. The first data set is to be determined by a single measurement of the spectrometric measuring device (single spectrometer) with the spectrometric calibration device according to the previously described procedure steps. The absolute spectral accuracy of this measurement should be in the range of ±0.2 nm or better. This absolute accuracy is ensured by the method according to the invention.

[0035] The simulated (synthetic) sample spectra are calculated by multiplying the sensitivity curve of each spectral channel of the spectrometric instrument with each sample spectrum of the second dataset. For this purpose, the sensitivity curves of the spectral channels and the sample spectra of the second dataset are interpolated to the same, ideally high, number of reference points (e.g., 350). At each reference point (wavelength), the sensitivity value is multiplied by the sample spectrum value. The calculated products are summed and normalized. This yields a value for the synthetic sample spectrum for each spectral channel. For a spectrometric instrument with, for example, N=16 spectral channels, this results in synthetic sample spectra with 16 reference points, which are subsequently used for chemometric calibration.

[0036] An advantage of the method according to the invention is that the combination of the two high-precision datasets allows for the creation of sufficiently accurate chemometric models without the need for repeated sample measurements with each individual spectrometric measuring device. This has been verified by corresponding simulation calculations. Thus, existing spectral databases (spectra with associated ingredient concentrations) can be used to create individual calibration models for each spectrometer. Advantageously, the previously common, error-prone manipulation and transfer of calibration models from one spectrometer to another of the same series is eliminated.

[0037] The spectral database containing the sample spectra can be created by a manufacturer or user, or it may already exist at the user's site. An exchange of information about the spectral database between a spectrometer owner and a user is conceivable, and this exchange could, for example, take place via the cloud.

[0038] In the present method, the spectrometric measuring device used simultaneously constitutes a receiver (device for acquiring a spectrum) and the object being measured (the object to be measured) during the calibration process. The spectrometric calibration device preferably includes a Michelson interferometer; however, in principle, it can also be any other type of optical interferometer.

[0039] To increase accuracy, the individual process steps can be performed multiple times. Error-corrected averages can then be calculated from the resulting values.

[0040] The preferred steps are acquiring the interferograms, from which the first data set is generated, and subsequently calculating the simulated spectra for different wavelengths of the broadband radiation source and / or different wavelengths of the laser. The wavelengths used for the first radiation source can be determined, for example, by filters. Typically, the wavelength of the second radiation source will be constant, although it is also possible for several selectable lasers to constitute the second radiation source.

[0041] In a preferred process step, the movable mirror is shifted along the beam path, thus increasing or decreasing the distance between the beam splitter and the movable mirror. This allows the various process steps to be repeated multiple times, with the movable mirror assuming different positions. In an alternative embodiment, the movable mirror is rotatable. An interferogram can be generated using the movable mirror.

[0042] A piezoelectrically driven linear adjustment stage or piezoelectric actuator can be used as a mirror adjustment device, which is particularly suitable for stepwise adjustment of the mirror. The step size is always chosen so that the Nyquist-Shannon sampling theorem is satisfied for the relevant wavelengths.

[0043] Alternatively, the mirror adjustment can be performed periodically and continuously, preferably using an electromagnetic drive. The necessary equidistance of the spatial mirror support points can be calculated from the temporal support points using the laser interferogram.

[0044] An alternative procedure involves storing the spectral properties of the spectrometric measuring device as a parameter set in the control unit of the spectrometric calibration device, provided that the parameters of the spectral channels of the spectrometric measuring device are known with sufficient accuracy. For filter-based spectrometers, the sensitivity profiles of the individual spectral channels can often be described using Lorentz functions. In this case, determining the peak wavelength and the full width at half maximum (FWHM) of the Lorentz functions for each spectral channel is sufficient.

[0045] The present invention thus also relates to a spectrometric calibration device for carrying out the inventive method for calibrating a spectrometric measuring device according to the aforementioned method steps. As already explained above, the calibration device comprises a control unit and a beam splitter. Furthermore, the measuring device comprises an interferometer with mirrors, wherein a first mirror is movable and a second mirror is stationary. The spectrometric calibration device further comprises two radiation sources, namely a broadband radiation source and a laser. The calibration device also comprises a measuring unit with at least one detector.

[0046] The spectrometric measuring device, which forms a temporary detector of the calibration device, has N spectral channels, each spectral channel having a peak wavelength λ(n) and a spectral full width at half maximum (FWHM) FWHM(n). Preferably, the spectral channels are located in the infrared (IR) range. Alternatively, and more preferably, the spectral channels are located in the visible (VIS) range or, more preferably, in the ultraviolet (UV) range. The spectral channels can also be located in several of the aforementioned ranges.

[0047] The simulated sample spectra preferably have multiple support points (N). In one example, the number of support points in the simulated sample spectra is N=16.

[0048] Preferably, the spectrometric calibration device comprises at least one further optical element which is arranged in the beam path and may be formed by a lens, a collimator, a dispersion compensation plate, a diffuser or the like, so that, for example, the light or the radiation emitted by the radiation sources is widened and / or homogenized.

[0049] In one embodiment, the spectrometric calibration device comprises a further mirror, namely a parabolic mirror, which is arranged in the beam path.

[0050] For example, components of the device are designed using MEMS technology.

[0051] While a conventional FTIR spectrometer measures the absorbing or reflecting spectral properties of an (organic) sample, a spectrometric calibration device measures the spectral sensitivity distribution of the spectrometric instrument. For example, if the spectrometric instrument is a filter-based spectrometer, the sensitivity curve is measured against the wavelength of each filter. If the spectrometric instrument to be calibrated has N spectral channels, N+1 interferograms are recorded synchronously. N interferograms are measured with the spectrometric instrument, and one additional interferogram is measured with the photodiode used for laser radiation detection.

[0052] Further advantages, details, and modifications of the invention will become apparent from the following description of a preferred embodiment, with reference to the drawing. The drawing shows: Fig. 1: a schematic view of a spectrometric calibration device according to the invention; Fig. 2: an interferogram of a single spectrometer channel of the spectrometric measuring device acquired with the spectrometric calibration device; and Fig. 3: a diagram of calculated sensitivity spectra of the spectrometric measuring device.

[0053] Fig. Figure 1 schematically shows the main components and the beam path of a spectrometric calibration device 01 according to the invention, which is configured to perform a method according to the invention for calibrating a spectrometric measuring device 20. The spectrometric calibration device 01 is a modified FTIR spectrometer and comprises an interferometer with a stationary mirror 02 and a movable mirror 03, as well as a beam splitter 04. Furthermore, the calibration device 01 comprises two radiation sources, wherein a first radiation source is a broadband radiation source 06 and a second radiation source is a laser 07. The broadband radiation source 06 can be a white light source in the form of a halogen lamp. The laser 07 can be a HeNe laser. The two radiation sources are arranged to be able to simultaneously illuminate the interferometer.Furthermore, the spectrometric calibration device 01 includes at least one first optical detector 08 for measuring the laser radiation, wherein the first optical detector 08 can be a photodiode. The photodiode serves to acquire an interferogram of the laser radiation. The spectrometric measuring device 20 to be calibrated is arranged in the beam path as a further detector 09, wherein the spectrometric measuring device 20 can be a grating spectrometer or a filter-based spectrometer.

[0054] Furthermore, the spectrometric calibration device 01 includes a control unit (not shown).

[0055] The two radiation sources 06, 07 of the calibration device 01 simultaneously emit radiation 12a, 12b towards the beam splitter 04, where the emitted radiation 12 is split. A first beam component 13a, 13b is reflected towards the stationary mirror 02, and a second beam component 14a, 14b is transmitted through the beam splitter 04 towards the movable mirror 03. When the first beam components 13a, 13b strike the stationary mirror 02, they are reflected back to the beam splitter 04 and transmitted through it. The second beam components 14a, 14b strike the movable mirror 03 and are reflected back towards the beam splitter 04. Subsequently, the first and second beams 13, 14 recombine to form a recombined beam 16 with the beam parts 16a, 16b.The recombined beam 16 enters the first detector 08 and the second detector 09. The first detector 08 provides an interferogram as a measurement signal from the interfering, recombined radiation 16 of the laser 07, the measurement signal depending on the position of the movable mirror 03. Likewise, the recombined beam 16 enters the spectrometric measuring device 20, and the associated second optical detector 09 determines – synchronously with the first detector 08 – from the interfering, recombined radiation of the broadband radiation source 16 as many additional measurement signals (interferograms) as the spectrometric measuring device has spectral channels (see figure). Fig. 2 and Fig. 3) The control unit of the spectrometric calibration device 01 generates a sensitivity spectrum for each spectral channel of the spectrometric measuring device 20 from each measured interferogram using FFT calculations (see Fig. 3) A spectrometer dataset with N sensitivity spectra is thus created. The laser interferogram is used to correct phase disturbances and non-equidistant step sizes of the drive device for the movable mirror 03.

[0056] The method involves generating a simulated sample spectrum dataset with reduced resolution (N spectral support points) from the measured spectrometer dataset (first dataset) using at least one high-resolution sample spectrum dataset (second dataset) with M spectral support points (M ≥ N) and corresponding ingredient concentrations, stored in the control unit or in an external database. The simulated sample spectra (with N spectral support points) of the single spectrometer are calculated by weighted multiplication of the high-resolution sample spectra with the spectral properties of the single spectrometer, which were measured by the spectrometric calibration device. The high-resolution sample spectrum dataset and the simulated sample spectrum dataset are two distinct datasets, each consisting of multiple sample spectra, preferably at least 50.Using the simulated sample spectrum dataset, at least one chemometric calibration model is created for a selected sample type (e.g., corn) for the spectrometric measuring device. The creation of the chemometric calibration model can be PLS1-based. In a further process step, the chemometric calibration model is used to predict ingredient concentrations based on sample spectra measured with the single spectrometer.

[0057] The aforementioned steps can be performed in the control unit of the spectrometric calibration device and / or the spectrometric measuring device and / or by an external computing unit.

[0058] Unlike a conventional FTIR spectrometer, the spectrometric calibration device according to the invention does not perform direct ingredient measurements of (organic) samples. Instead, the spectrometric measuring device to be calibrated acts as the sample during calibration, with the spectrometric measuring device temporarily functioning as part of the calibration device and contributing the spectrally resolving detector for the broadband lamp radiation.

[0059] The described method makes it possible to create chemometric calibration models for numerous spectrometers with large manufacturing variations without having to perform a large number of sample measurements with each individual spectrometer. This allows existing spectral databases (spectra with associated ingredient concentrations) to be used to create individual calibration models for each spectrometer. The previously common, error-prone manipulation and transfer of calibration models from one spectrometer to another is thus eliminated.

[0060] Fig. Figure 2 shows an example of an interferogram of a single spectrometer channel of the spectrometric measuring device (single spectrometer) acquired with the spectrometric calibration device 01, wherein the single spectrometer used is a 16-channel filter spectrometer.

[0061] In Fig.Figure 3 shows sensitivity spectra of a 16-channel filter spectrometer calculated from 16 interferograms, which were generated according to the method according to the invention. Reference symbol 01 spectrometric calibration device 02 stationary mirror 03 movable mirror 04 Beam splitter 05 - 06 broadband radiation source 07 Laser 08 optical detector for measuring laser radiation 09 additional optical detector for measuring broadband radiation 10 - 11 - 12 emitted radiation 13 first beam parts 14 second beam sections 15 - 16 recombinant beam 20 spectrometric measuring devices

Claims

[1] Method for calibrating a spectrometric measuring device (20) with a spectrometric calibration device (01), wherein the calibration device (01) has a control unit, an interferometer with mirrors (02, 03) and a beam splitter (04), wherein a first mirror (03) is movable and a second mirror (02) is stationary, a broadband first radiation source (06), a laser (07) as a second radiation source and a first detector (08), wherein the method comprises the following steps: - Emitting a broadband electromagnetic radiation (12a) by the broadband radiation source (06) and simultaneously emitting an electromagnetic radiation (12b) by the laser (07), and simultaneously coupling these two radiations (12a, 12b) into the interferometer of the calibration device; - detecting a first interferogram based on the radiation (12b) of the laser (07) by the first detector (08); - detecting a second interferogram based on the radiation (12a) of the broadband radiation source (06) by the spectrometric measuring device (20), synchronously with the detection of the first interferogram; - creating a first data set with the spectral properties of the spectrometric measuring device (20) on the basis of the acquired interferograms; - Providing a second data set consisting of precise, high-resolution sample spectra and associated chemically determined constituent values; - Calculation of simulated sample spectra from the two data sets; and - Creation of a chemometric calibration model from the simulated sample spectra for the spectrometric measuring device (20) and storage of the chemometric calibration model. [2] Method according to claim 1, characterized bythat the chemometric calibration model is calculated using a partial least squares regression calibration. [3] Method according to one of claims 1 to 2, characterized by that the acquisition of the interferograms and subsequent calculation of the simulated sample spectra is carried out sequentially for different ingredients. [4] Method according to one of claims 1 to 3, characterized by that the interferograms are recorded by setting equidistant or non-equidistant mirror positions of the movable mirror (03). [5] Method according to one of claims 1 to 4, characterized by that the provision of the first data set and / or the second data set and their calculation to the chemometric calibration model takes place via a data cloud. [6] Method according to one of claims 1 to 5, characterized by that the simulated sample spectrum has N spectral support points, where N≥16. [7] Spectrometric calibration device (01) comprising a control unit and an interferometer with mirrors (02, 03) and with a beam splitter (04), wherein a first mirror (03) is movable and a second mirror (02) is stationary, further comprising a broadband radiation source (06), a laser (07) as a second radiation source, a first detector (08) for detecting interferograms of the radiation emitted by the laser (07), and a further detector (09) which is formed by a spectrometric measuring device (20) to be calibrated, characterized by that the calibration device (01) is designed to carry out a method according to one of claims 1 to 6. [8] Spectrometric calibration device (01) according to claim 7, characterized by that the mirrors (02, 03) are designed as angle error compensating retro-reflectors. [9] Spectrometric calibration device (01) according to claim 7 or 8, characterized bythat the movable mirror (03) is driven by a piezo actuator or a magnetic actuator. [10] Spectrometric calibration device (01) according to one of claims 7 to 9, characterized by that the radiation of the broadband radiation source (06) is supplied via a separate measuring head which is coupled to the calibration device (01) via an optical fiber. [11] Spectrometric calibration device (01) according to claim 10, characterized by that the measuring head contains angle spectrum-changing components, in particular lenses, diffusers or microlens arrays. [12] Spectrometric calibration device (01) according to one of claims 7 to 9, characterized by that the radiation of the broadband radiation source (06) and / or the laser (07) is guided as a free beam and / or in optical fibers and / or in photonic integrated circuits (PICs). [13] Spectrometric calibration device (01) according to one of claims 7 to 12, characterized by that at least some of its components are implemented using MEMS technology.

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