Method for calibrating a spectrometric measuring device and spectrometric calibration device for carrying out the method
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- CARL ZEISS MICROSCOPY GMBH
- Filing Date
- 2024-11-13
- Publication Date
- 2026-07-01
AI Technical Summary
Existing spectrometric measuring devices in series exhibit manufacturing variations, leading to differences in peak wavelength and spectral half-width, which complicates the exchange of chemometric calibration models between devices, requiring time-consuming and costly correction measurements with real samples.
A method using a spectrometric calibration device with an FTIR spectrometer, a broadband radiation source, and a reference laser to achieve high absolute spectral accuracy of 0.2 nm or better, allowing for the creation of chemometric calibration models without the need for repeated sample measurements on individual spectrometers.
This method enables precise calibration of spectrometric measuring devices, allowing for the creation of chemometric calibration models that are accurate and consistent across devices with manufacturing variations, reducing the need for costly sample measurements and improving the efficiency of ingredient analysis.
Smart Images
Figure EP2024082158_30052025_PF_FP_ABST
Abstract
Description
[0001] Method for calibrating a spectrometric measuring device and spectrometric calibration device for carrying out the method
[0002] The present invention relates to a method for calibrating a spectrometric measuring device. Furthermore, the invention relates to a spectrometric calibration device suitable for carrying out this method.
[0003] 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 primarily used in agriculture and the food industry. To achieve high levels of accuracy in such analyses, the measuring device must be appropriately calibrated.
[0004] For ingredient analysis, the spectrometric measuring device (hereinafter also referred to as a spectrometer) records spectral measured values of the sample, which are influenced by the sample's ingredients. By applying a chemometric model, the concentration of at least one ingredient to be analyzed is determined from the spectral measured values. The result is a value for the concentration of at least one ingredient in the sample. Chemometric methods are used to analyze data using algorithms. Those skilled in the art are aware 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 also referred to below as spectral measured values.
[0005] It is common practice to equip spectrometric measuring devices with line sensors and perform wavelength calibration using a few, highly accurate, known spectral lines from low-pressure lamps. Typically, a grating spectrometer with a line sensor is used, for example, a Si-based one operating in the ultraviolet (UV) or visible (VIS) range, or an InGaAs-based one operating in the infrared range. Alternatively, filter-based spectrometers can be used, which are usually spectrally calibrated with monochromators. Various calibration methods using specific wavelengths and / or scattered light are known.
[0006] Industrially manufactured spectrometers within a series exhibit significant manufacturing variations. Until now, it has been a challenging approach to produce numerous spectrometers within a series with spectral properties that are as similar as possible so that the sometimes laboriously created chemometric calibration models can be exchanged between the individual instruments. However, due to manufacturing reasons, the peak wavelength and / or the spectral half-width of the spectral channels usually vary by significantly more than 0.2 nm between individual instruments. This means that similar properties can no longer be assumed, and chemometric calibration models created once can no longer be easily applied to multiple instruments within a series. This problem occurs particularly with spectrometers using interference filters, especially polymer-based interference filters produced by vapor deposition.Since it is difficult in practice to equip all spectrometers in 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 the specific instrument. This is time-consuming and costly, as numerous sample measurements must be performed on each individual spectrometer.
[0007] Therefore, a calibration procedure is desirable that eliminates the need to vary chemometric models to make them available to other spectrometers of the same type, since this approach usually requires additional sample measurements and is associated with a loss of accuracy in the component analysis.
[0008] A problem of spectrometric calibration is addressed in WO 2023 / 066896 A1. Accordingly, for successful application, spectrographic methods require reliable performance of the spectrographic instruments with negligible fluctuations, particularly when comparing measurements from different spectrographic instruments. In particular, the spectral data for a given sample should be at least similar or identical for different spectrographic instruments of the same type. To solve this problem, WO 2023 / 066896 A1 proposes a calibration method for a spectrometric device. The device comprises at least one detector unit, at least one optical element for splitting a light beam into wavelength components, and a plurality of photosensitive elements for detecting the wavelength components and generating a detector signal from the wavelength components.The light beam is generated using 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 method step is described for determining calibration information. Overall, however, the previously known calibration method is not precise enough to perform a fast, inexpensive, and precise calibration for devices with significantly different properties. WO 2023 / 066896 A1 does not address the creation of chemometric calibrations or chemometric models.
[0009] DE 102014 226 487 A1 describes an FTIR spectrometer with 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 by the reference laser source is guided through an absorption medium to a reference detector. The absorption medium has an absorption line in the tuning range of the reference laser source. Electronics allow the laser wavelength to be adjusted to the absorption line of the absorption medium using a signal from the reference detector. This is intended to achieve improved stabilization of the laser wavelength of the reference laser.
[0010] US 2023 / 0304860 A1 describes a spectral modeling system for creating chemometric calibration models for spectral instruments. The approach described therein aims at creating and using a uniform chemometric calibration model for a large number of similar spectral instruments. The spectral modeling system described for this purpose includes a spectral converter. The spectral converter is used to generate a large number of artificial spectra using spectral data from a large number of samples measured by a subset of a large number of spectral instruments, as well as spectral instrument properties that represent spectral variations in the large number of spectral instruments.The spectral modeling system further includes an engine for generating a unified chemometrics model for one or more parameters associated with the plurality of samples based on the spectral data and the plurality 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 in a series can be calibrated with a high absolute spectral accuracy of 0.2 nm or better, in order to achieve satisfactory accuracy in the chemometric determination of sample constituents with the calibrated measuring device. Furthermore, it is an object of the present invention to provide a spectrometric calibration device that can carry out such a method for calibrating a spectrometric measuring device.
[0012] These objects are achieved by a method according to the invention according to the appended claim 1 and by a spectrometric calibration device according to the independent claim 7.
[0013] The method according to the invention serves to calibrate a spectrometric measuring device using a spectrometric calibration device. 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, a "spectral calibration" is meant. If the calibration refers to the creation of a chemometric model, a "chemometric calibration" is meant, which is often also referred to as a "beta vector." Both types of calibration are necessary components of an improved ingredient analysis using the measuring device calibrated according to the invention.
[0014] The preferred spectrometric calibration device for performing this 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 gradually changing the wavelength, but rather is calculated by a Fourier transform of a measured interferogram.
[0015] The spectrometric measuring device to be calibrated can be, for example, a grating spectrometer or a filter-based spectrometer.
[0016] 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
[0017] Detector. The first radiation source is a broadband radiation source, the second radiation source is a reference laser (hereinafter also referred to simply as a laser). The broadband radiation source can be a halogen lamp. Alternative broadband radiation sources include 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 operating mode. A HeNe laser is preferably used as the laser. The wavelength of the laser is therefore 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 both in terms of wavelength and intensity, the technical means suitable for this being known to the person skilled in the art and need not be described in detail here.
[0018] The method according to the invention for calibrating a spectrometric measuring device then comprises the following method steps:
[0019] In a first process step, the broadband radiation source is caused to emit broadband electromagnetic radiation. At the same time, the laser emits electromagnetic radiation with a precisely known wavelength. The broadband radiation source and the laser are arranged to emit in the same beam path, so that the two different electromagnetic radiations simultaneously radiate into the interferometer of the spectrometric calibration unit, which is arranged 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 simultaneously, the total measurement time required for the calibration process can be significantly reduced. Furthermore, the usable light value is increased.
[0020] 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 partially guided 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 partially guided in optical fibers. Alternatively, the radiation from the radiation sources is preferably guided entirely in photonic integrated circuits (PICs). Alternatively, the radiation from the radiation sources is partially guided in photonic integrated circuits (PICs).
[0021] 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 a fiber optic cable. The measuring head preferably contains angle-spectrum-modifying components, such as lenses, diffusers, or microlens arrays.
[0022] 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 guided to the stationary mirror of the interferometer and is reflected therefrom back to the beam splitter, and wherein each second beam passes through or passes the beam splitter and is reflected back to the beam splitter at the movable mirror of the interferometer.
[0023] The beams reflected back to the beam splitter (originally emitted by both radiation sources) exit the beam splitter as recombined radiation, with the first beams passing through the beam splitter and the second beams being reflected by the beam splitter. The recombined radiation is then directed to the measuring unit with detector.
[0024] In a further process step, a first interferogram is measured with the detector. The complex superposition of the recombined radiation in the area of the measuring unit results in interference effects. The interfering, recombined laser radiation is preferentially fed to a photodiode acting as a detector and sensitive to the laser radiation wavelength.
[0025] In a further method step, further interferograms are measured based on the radiation from the broadband radiation source by the spectrometric measuring device, synchronously with the acquisition of the first interferogram of the laser. The spectrometric measuring device to be 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 guided to the spectrometric measuring device. The spectrometric measuring device is thus a temporary component of the spectrometric calibration device during the calibration process and temporarily forms the spectrally resolving detector for the broadband radiation. The spectrometric calibration device (FTIR spectrometer) preferably comprises a measuring head connected to the spectrometric measuring device to be calibrated via a fiber optic cable.The measuring head preferably contains an optical diffuser and other optical elements, as well as spectral selection elements, which are used to simulate the angular spectrum of a reflecting sample as closely as possible using the lamp illumination. This is advantageous because the angular spectrum of the detector illumination influences the spectral detection properties of the spectrometric measuring device.
[0026] Since both radiation sources are coupled simultaneously into the spectrometric calibration device and their interfering radiation is detected simultaneously, the laser radiation experiences the same phase disturbances as the broadband radiation. This makes it possible to use the laser interferogram to mathematically eliminate the phase disturbances in the interferogram of the broadband radiation (lamp interferogram). It is important that the intensity measurements are performed synchronously with the photodiode, as the detector of the electromagnetic radiation emitted by the laser, and with the spectrometric measuring device to be calibrated, as the temporary detector of the broadband electromagnetic radiation emitted by the lamp.
[0027] To create the interferograms, the position of the movable mirror must be changed. For this purpose, the spectrometric calibration device preferably comprises a mirror adjustment device. The interferograms are acquired by setting equidistant or non-equidistant mirror positions of the movable mirror. One advantage of the inventive device that can be used in this context is
[0028] The advantage of this method is that the spectrometric calibration device compensates for positioning errors of the mirror adjustment device when it is operated step by step.
[0029] Alternatively, the spectrometric calibration device can be operated with a continuous (periodic) movement of the mirror adjustment device. In this case, too, the laser interference signal can be used to detect the mirror movement with high precision and serve as a correction signal during spectrometric calibration.
[0030] The mirrors can preferably be formed by retroreflectors. In particular, the mirror can be an angle-compensating retroreflector (corner cube). Preferably, the beams from the two radiation sources are superimposed collinearly so that they radiate through the same volumes of air at all times. Optical components arranged in the beam path, preferably dichroic beam splitters, are used for the superposition. 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 refractive index of the air.
[0031] Alternatively, the beams from the two radiation sources are superimposed concentrically, with one radiation source predominantly using an inner region with a smaller beam diameter and the other radiation source predominantly using an outer region with a larger beam diameter. In this embodiment, the beams are preferably superimposed by using mirrors with a hole for coupling and decoupling. 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 broadband lamp radiation is coupled in and out by reflection from the mirrors. Alternatively, the lamp radiation can be guided through the holes and the laser radiation reflected.
[0032] The laser provides a highly accurate, known reference wavelength measurement for each measurement, thereby achieving improved absolute wavelength accuracy in the spectral calibration of the spectral measurement device. The optical path difference or path length difference (OPD) can be determined using the laser's reference wavelength measurement.
[0033] In a further process step, a first data set is created containing the spectral properties of the spectrometric measuring device based on the acquired interferograms. A second data set is then provided, consisting of precise, high-resolution sample spectra and the corresponding, chemically determined constituent values. Simulated sample spectra are then calculated from these two data sets.
[0034] 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 (individual spectrometers). PLS calibration (partial least squares regression) is preferably used to create the chemometric calibration model. A machine learning system can be used to create the chemometric calibration model.
[0035] To generate the simulated sample spectra, the aforementioned at least two data sets are used. The first data set contains the spectral properties of the individual spectrometer that will later be used for ingredient measurements. The second data set includes high-resolution and wavelength-accurate sample spectra, as well as the corresponding ingredient concentrations. The optical spectra of the second data set should be so precise that they can be considered spectrometrically correct, as they form the basis for simulating the synthetic sample spectra, which are used to create chemometric calibration models for the spectroscopic measuring device. Such data sets are generated with great effort. The second data set can, for example, be taken from existing databases.Alternatively, it can be recorded with a precise, high-resolution master spectrometer, which can also be calibrated with the spectrometric calibration device. Typically, the master spectrometer 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 one-time measurement of the spectrometric measuring device (individual spectrometer) with the spectrometric calibration device according to the method steps described above. The absolute spectral accuracy of this measurement is to be set in the range of +0.2 nm or better. This absolute accuracy is ensured by the method according to the invention.The simulated (synthetic) sample spectra are calculated by multiplying the sensitivity curve of each spectral channel of the spectrometric measuring device with each sample spectrum of the second data set. To do this, the sensitivity curves of the spectral channels and the sample spectra of the second data set are interpolated to the same, highest possible number of sampling points (e.g., 350). At each sampling point (wavelength), the sensitivity value is multiplied by the sample spectrum value. The calculated products are summed and normalized. This yields a value of the synthetic sample spectrum for each spectral channel. For a spectrometric measuring device with, for example, N=16 spectral channels, synthetic sample spectra with 16 sampling points are obtained, which are subsequently used for chemometric calibration.
[0036] An advantage of the method according to the invention is that by combining the two highly accurate data sets, sufficiently precise chemometric models can be created without having to perform repeated sample measurements with each individual spectrometric measuring device. This was verified by corresponding simulation calculations. Thus, existing spectral databases (spectra with associated constituent concentrations) can be used to create individual calibration models for each individual spectrometer. Advantageously, the previously common, error-prone manipulation and transfer of calibration models from one spectrometer to another of the same series is no longer necessary.
[0037] The spectral database containing the sample spectra can be created by a manufacturer or user, or may already be available at the user's site. An exchange of spectral database contents between a spectrometer owner and a user is conceivable, with the exchange being possible, for example, via a cloud-based platform.
[0038] In the present method, the spectrometric measuring device used during the calibration process simultaneously represents a receiver (device for capturing a spectrum) and the measurement object (the object to be measured) itself. 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 repeated multiple times. The resulting values can be used, for example, to calculate error-corrected averages.
[0040] Preferably, the steps of acquiring the interferograms from which the first data set is formed and the subsequent calculation of the simulated spectra are performed for different wavelengths of the broadband radiation source and / or different wavelengths of the laser. The wavelengths used by 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 form the second radiation source.
[0041] In a preferred method step, the movable mirror is moved along the beam path so that the distance between the beam splitter and the movable mirror decreases or increases. Thus, the various method steps can be repeated several times, with the movable mirror assuming different positions. In an alternative variant, the movable mirror is rotatable. Using the movable mirror, an interferogram can be created.
[0042] A piezo-driven linear stage or piezo actuator, for example, can be used as a mirror adjustment device, which is particularly suitable for stepwise adjustment of the mirror. The step size is always selected so that the Nyquist-Shannon sampling theorem is observed for the relevant wavelengths.
[0043] Alternatively, the mirror adjustment can be performed periodically and continuously, preferably using an electromagnetic drive. The required equidistance between the spatial mirror support points can be calculated from the temporal support points using the laser interferogram.
[0044] An alternative method step involves storing the spectral properties of the spectrometric measuring device as a parameter set in the control unit of the spectrometric calibration device, provided the parameters of the spectral channels of the spectrometric measuring device are known with sufficient accuracy. In filter-based spectrometers, the sensitivity curves of the individual spectral channels can often be described using Lorentz functions. In this case, determining the peak wavelength and the half-width 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.
[0046] Furthermore, the calibration device comprises a measuring unit with at least one detector.
[0047] The spectrometric measuring device, which forms a temporary detector of the calibration device, has N spectral channels, each spectral channel having a peak wavelength X(n) and a spectral half-width FWHM(n). The spectral channels are preferably in the infrared (IR) range. Alternatively, the spectral channels are preferably in the visible (VIS) range or, preferably, in the ultraviolet (UV) range. The spectral channels can also be in several of the aforementioned ranges.
[0048] The simulated sample spectra preferably have multiple sampling points (N). In one example, the number of sampling points of the simulated sample spectra is N=16.
[0049] The spectrometric calibration device preferably comprises at least one further optical element, which is arranged in the beam path and can 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 expanded and / or homogenized. 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 records the absorbing or reflecting spectral properties of an (organic) sample, the spectrometric calibration device measures the spectral sensitivity distribution of the spectrometric measuring device. For example, if the spectrometric measuring device is a filter-based spectrometer, the sensitivity curve is measured over the wavelength of each filter.
[0052] If the spectrometric measuring device to be calibrated has N spectral channels, N+1 interferograms are recorded synchronously. N interferograms are measured with the spectrometric measuring device, and another interferogram is measured with the photodiode intended for detecting the laser radiation.
[0053] Further advantages, details, and modifications of the invention will become apparent from the following description of a preferred embodiment, with reference to the drawings.
[0054] Fig. 1: a schematic view of a spectrometric calibration device according to the invention;
[0055] 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.
[0056] Fig. 1 schematically shows the main components and the beam path of a spectrometric calibration device 01 according to the invention, which is designed to carry out a method according to the invention for calibrating a spectrometric measuring device 20. The spectrometric calibration device 01 is an adapted FTIR spectrometer and comprises an interferometer with a stationary mirror 02 and a movable mirror 03, as well as with a beam splitter 04. Furthermore, the calibration device 01 comprises two radiation sources, a first radiation source being a broadband radiation source 06 and a second radiation source being 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 formed by a HeNe laser. The two radiation sources are arranged so that they can radiate into the interferometer simultaneously.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 detect 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. The spectrometric measuring device 20 can be a grating spectrometer or a filter-based spectrometer.
[0057] Furthermore, the spectrometric calibration device 01 comprises a control unit (not shown). The two radiation sources 06, 07 of the calibration device 01 each simultaneously emit a radiation 12a, 12b in the direction of the beam splitter 04, where the emitted radiation 12 is split so that a first beam portion 13a, 13b is reflected in the direction of the stationary mirror 02 and a second beam portion 14a, 14b is transmitted through the beam splitter 04 in the direction of the movable mirror 03. If the first beam parts 13a, 13b hit the stationary mirror 02, they are reflected back to the beam splitter 04 and transmitted through the beam splitter 04. The second beam parts 14a, 14b hit the movable mirror 03 and are reflected back by it in the direction of the beam splitter 04 and reflected at the beam splitter 04.
[0058] Subsequently, the first and second beams 13, 14 recombine to form a recombined beam 16 with beam portions 16a, 16b. The recombined beam 16 impinges on the first detector 08 and the second detector 09. The first detector 08 delivers an interferogram from the interfering, recombined radiation 16 of the laser 07 as a measurement signal, with 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 further optical detector 09 associated with it determines - synchronously with the first detector 08 - from the interfering, recombined radiation of the broadband radiation source 16 as many further measurement signals (interferograms) as the spectrometric measuring device has spectral channels (cf. Fig. 2 and Fig. 3).The control unit of the spectrometric calibration device 01 uses FFT calculations to generate a sensitivity spectrum for each spectral channel of the spectrometric measuring device 20 from each measured interferogram (see Fig. 3). Thus, a spectrometer data set with N sensitivity spectra is created. The laser interferogram is used to correct phase disturbances and non-equidistant step sizes of the drive device for the movable mirror 03.
[0059] The method provides for a simulated sample spectrum dataset with reduced resolution (N spectral support points) to be generated 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 associated ingredient concentrations stored in the control unit or in an external database. The calculation of the simulated sample spectra (with N spectral support points) of the individual spectrometer is carried out by weighted multiplication of the high-resolution sample spectra by the spectral properties of the individual spectrometer, which were measured by the spectrometric calibration device. The high-resolution sample spectrum dataset and the simulated sample spectrum dataset are two different datasets consisting of several sample spectra, preferably at least 50 sample spectra.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 chemometric calibration model can be created using PLCs. The chemometric calibration model is used in a subsequent process step to predict ingredient concentrations based on sample spectra measured with the individual spectrometer.
[0060] The above steps can be carried out in the control unit of the spectrometric calibration device and / or the spectrometric measuring device and / or by an external computing unit.
[0061] Unlike a conventional FTIR spectrometer, the spectrometric calibration device according to the invention does not perform direct component measurements of (organic) samples. Instead, the spectrometric measuring device to be calibrated acts as the measurement sample during calibration, with the spectrometric measuring device temporarily functioning as a component of the calibration device and providing the spectrally resolving detector for the broadband lamp radiation.
[0062] 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. Thus, existing spectral databases (spectra with associated constituent concentrations) can be used to create individual calibration models for each individual spectrometer. This eliminates the previously common, error-prone manipulation and transfer of calibration models from one spectrometer to another.
[0063] Fig. 2 shows an example of an interferogram of a single spectrometer channel of the spectrometric measuring device (single spectrometer) recorded with the spectrometric calibration device 01, wherein the single spectrometer used is a 16-channel filter spectrometer.
[0064] Fig. 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 numerals
[0065] 01 spectrometric calibration device
[0066] 02 stationary mirror
[0067] 03 movable mirror
[0068] 04 Beam splitter
[0069] 05
[0070] 06 broadband radiation source
[0071] 07 Laser
[0072] 08 optical detector for measuring laser radiation
[0073] 09 additional optical detector for measuring broadband
[0074] radiation
[0075] 10
[0076] 11
[0077] 12 emitted radiation
[0078] 13 first beam parts
[0079] 14 second beam parts
[0080] 15
[0081] 16 recombined beam
[0082] 20 spectrometric measuring devices
Claims
Patent claims 1. A 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); the method comprising 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 in that the chemometric calibration model is calculated by means of a partial least squares regression calibration.
3. Method according to one of claims 1 to 2, characterized in that the acquisition of the interferograms and subsequent calculation of the simulated sample spectra are carried out successively for different ingredients.
4. Method according to one of claims 1 to 3, characterized in that the detection of the interferograms is carried out by setting equidistant or non-equidistant mirror positions of the movable mirror (03).
5. Method according to one of claims 1 to 4, characterized in 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 in 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 in that the calibration device (01) is set up to carry out a method according to one of claims 1 to 6.
8. Spectrometric calibration device (01) according to claim 7, characterized in 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 in that 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 in 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 in 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 in 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 in that at least some of its components are designed using MEMS technology.