DETECTOR WITH TEMPERATURE DRIFT COMPENSATION

Abstract

Disclosed herein is a method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas of at least one detector. The measurement signal S.sub.meas includes the AC signal S.sub.AC and at least one direct current (DC) signal S.sub.DC. The AC signal S.sub.AC has at least one predefined frequency f.sub.0. The method includes the following steps: a) monitoring the measurement signal S.sub.meas over time by using the detector; b) determining the DC signal S.sub.DC by using at least one evaluation unit; and c) determining the AC signal S.sub.AC by subtracting the DC signal S.sub.DC from the measurement signal S.sub.meas by using the evaluation unit.

Also disclosed herein are a method for determining at least one item of information on at least one measurement object, a photodetector and a spectrometer.

Claims

1. A method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas of at least one detector, wherein the measurement signal S.sub.meas comprises the AC signal S.sub.AC and at least one direct current (DC) signal S.sub.DC, wherein the AC signal S.sub.AC has at least one predefined frequency f.sub.0, the method comprising the following steps: a) monitoring the measurement signal S.sub.meas over time by using the detector; b) determining the DC signal S.sub.DC by using at least one evaluation unit, wherein the determining comprises evaluating the measurement signal S.sub.meas by using at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0; and c) determining the AC signal S.sub.AC by subtracting the DC signal S.sub.DC from the measurement signal S.sub.meas by using the evaluation unit.

2. The method according to claim 1, wherein the detector comprises at least one photodetector comprising at least one photosensitive region, wherein step a) comprises measuring the measurement signal S.sub.meas by using the photosensitive region of the photodetector, wherein the measurement signal S.sub.meas is dependent on an illumination of the photosensitive region.

3. The method according to claim 1, wherein in step b) the DC signal S.sub.DC is determined by further using a phase of the measurement signal S.sub.meas, wherein the evaluation of the measurement signal S.sub.meas comprises determining local minima of the measurement signal S.sub.meas by using the phase and at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0, wherein the DC signal S.sub.DC is determined by using the local minima.

4. The method according to claim 3, wherein the evaluation of the measurement signal S.sub.meas comprises fitting the DC signal S.sub.DC to the local minima of the measurement signal S.sub.meas, wherein the DC signal S.sub.DC is a function S.sub.DC(t) over time comprising at least one of a polynomial function having at least one fit parameter, an exponential function having at least one fit parameter, a square root function having at least one fit parameter and a logarithmic function having at least one fit parameter.

5. The method according to claim 1, wherein in step b) the DC signal S.sub.DC is determined by transforming the measurement signal S.sub.meas into a frequency domain, wherein the measurement signal S.sub.meas is transformed into the frequency domain by using a Fourier transformation.

6. The method according to claim 1, wherein the evaluation of the measurement signal S.sub.meas comprises filtering the transformed measurement signal S.sub.meas for at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0, wherein the evaluation of the measurement signal S.sub.meas comprises using the filtered transformed measurement signal S.sub.meas for determining the DC signal S.sub.DC.

7. The method according to claim 6, wherein the evaluation of the measurement signal S.sub.meas comprises fitting the DC signal S.sub.DC to the filtered transformed measurement signal S.sub.meas, wherein the DC signal S.sub.DC is a function S.sub.DC(t) over time comprising at least one of a polynomial function having at least one fit parameter, an exponential function having at least one fit parameter, a square root function having at least one fit parameter and a logarithmic function having at least one fit parameter.

8. The method according to claim 1, wherein the detector comprises the evaluation unit and/or at least one interface for transmitting data from and/or to and/or within the evaluation unit, wherein the evaluation unit is at least partially cloud based.

9. The method according to claim 1, wherein the method is at least partially computer-implemented.

10. A method for determining at least one item of information on at least one measurement object by using at least one detector, the method comprising the following steps: i) determining at least one measurement signal S.sub.meas by using the detector; ii) determining the AC signal S.sub.AC by using the method according to claim 1; and iii) determining the item of information on the measurement object by evaluating the AC signal S.sub.AC by using the evaluation unit (128).

11. A non-transient computer-readable medium including instructions that, when executed by one or more processors, cause the one or more processors to perform the method according to claim 1.

12. A photodetector for measuring optical radiation, the photodetector being configured for performing the method according to claim 1, wherein the photodetector comprises at least one photosensitive region.

13. A spectrometer for spectrally analyzing optical radiation provided by at least one measurement object, the spectrometer comprising: at least one radiation source configured for emitting optical radiation at least partially towards the measurement object; and at least one photodetector according to claim 12.

14. The spectrometer according to claim 13, wherein the radiation source is a modulated radiation source, wherein the radiation source is modulated at the frequency f.sub.0.

15. A method of using the spectrometer according to claim 13, the method comprising using the spectrometer for a purpose of use selected from the group consisting of: an infrared detection application; a heat detection application; a thermometer application; a heat-seeking application; a flame-detection application; a fire-detection application; a smoke-detection application; a temperature sensing application; a spectroscopy application; an exhaust gas monitoring application; a combustion process monitoring application; a pollution monitoring application; an industrial process monitoring application; a chemical process monitoring application; a food processing process monitoring application; a water quality monitoring application; an air quality monitoring application; a quality control application; a temperature control application; a motion control application; an exhaust control application; a gas sensing application; a gas analytics application; a motion sensing application; a chemical sensing application; a mobile application; a medical application; a mobile spectroscopy application; a food analysis application; an agricultural application; and a cosmetic application.

16. A non-transient computer-readable medium including instructions that, when executed by one or more processors, cause the one or more processors to perform the method according to claim 10.

17. A photodetector for measuring optical radiation, the photodetector being configured for performing the method according to claim 10, wherein the photodetector comprises at least one photosensitive region.

18. A spectrometer for spectrally analyzing optical radiation provided by at least one measurement object, the spectrometer comprising: at least one radiation source configured for emitting optical radiation at least partially towards the measurement object; and at least one photodetector according to claim 17.

19. The spectrometer according to claim 18, wherein the radiation source is a modulated radiation source, wherein the radiation source is modulated at the frequency f.sub.0.

20. A method of using the spectrometer according to claim 18, the method comprising using the spectrometer for a purpose of use selected from the group consisting of: an infrared detection application; a heat detection application; a thermometer application; a heat-seeking application; a flame-detection application; a fire-detection application; a smoke-detection application; a temperature sensing application; a spectroscopy application; an exhaust gas monitoring application; a combustion process monitoring application; a pollution monitoring application; an industrial process monitoring application; a chemical process monitoring application; a food processing process monitoring application; a water quality monitoring application; an air quality monitoring application; a quality control application; a temperature control application; a motion control application; an exhaust control application; a gas sensing application; a gas analytics application; a motion sensing application; a chemical sensing application; a mobile application; a medical application; a mobile spectroscopy application; a food analysis application; an agricultural application; and a cosmetic application.

Description

SHORT DESCRIPTION OF THE FIGURES

[0147] Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not restricted by the preferred embodiments. The embodiments are schematically depicted in the Figures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.

[0148] In the Figures:

[0149] FIG. 1 schematically shows an exemplary embodiment of a spectrometer according to the present invention;

[0150] FIG. 2 schematically shows an exemplary embodiment of a photodetector according to the present invention;

[0151] FIG. 3 shows a flow chart of an exemplary embodiment of a method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas according to the present invention;

[0152] FIGS. 4-6B show experimental results of measurements on an exemplary embodiment of a spectrometer according to the present invention; and

[0153] FIG. 7 shows a flow chart of an exemplary embodiment of a method for determining at least one item of information on at least one measurement object according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0154] FIG. 1 schematically shows an exemplary embodiment of a spectrometer 110 according to the present invention. The spectrometer 110 is configured for spectrally analyzing optical radiation 112 provided by at least one measurement object 114. The optical radiation 112 may specifically be within at least one of the visible, the ultraviolet or the infrared spectral range. Preferably, the optical radiation 112 which is used for typical purposes of the present invention is IR radiation, more preferred, NIR radiation, especially of a wavelength of 760 nm to 3 m, preferably of 1 m to 3 m. The optical radiation 112 may be provided by the measurement object 114. The providing may comprise at least one of a reflecting, transmitting and emitting. The measurement object 114 may be an arbitrary body, chosen from a living body and a non-living body. The measurement object 114 may specifically comprise at least one material which is subject to an investigation. The measurement object 114 may generally refer to an object which is to be measured, e.g. for which a spectrum is to be recorded, wherein the measurement object 114 may have in principle arbitrary properties, e.g. arbitrary optical properties or an arbitrary shape. The measurement object 114 may comprise at least one solid sample. However, other measurement objects such as fluids may also be feasible.

[0155] The spectrometer 110 may be an apparatus which is configured for determining spectral information by recording at least one measured value for at least one signal intensity related to at least one corresponding signal wavelength of the optical radiation 112 and by evaluating at least one measurement signal which relates to the signal intensity. The spectrometer 110 comprises at least one radiation source 116 configured for emitting the optical radiation 112 at least partially towards the measurement object 114. The radiation source 116 may be a device configured for emitting the optical radiation 112. The radiation source 116 may be configured for emitting the optical radiation 112 towards the measurement object 114, such as in form of a light beam 118. The radiation source 116 may be configured for isotopically emitting the optical radiation 112, e.g. uniformly in all spatial directions, wherein only a part of the emitted optical radiation 112 may impinge the measurement object 114. The radiation source 112 may comprise at least one of a semiconductor-based radiation source or a thermal radiator. The at least one semiconductor-based radiation source may be selected from at least one of a light emitting diode (LED) or a laser, specifically a laser diode. The LED may comprise at least one fluorescent and/or phosphorescent material. The thermal radiator may comprise at least one of an incandescent lamp, a black body emitter and a microelectromechanical system (MEMS) emitter.

[0156] The optical radiation 112 may be modulated, e.g. by using a modulated radiation source 120. In other words, the radiation source 116 may be a modulated radiation source 120. The radiation source 112 may be modulated at the frequency f.sub.0. Thus, the frequency f.sub.0 and overtones of the frequency f.sub.0 may be present in the optical radiation 112. The modulating may be a process of changing, specifically periodically changing, at least one property of optical radiation, specifically one or both of an intensity or a phase of the optical radiation. The modulation may be a full modulation from a maximum value to zero, or may be a partial modulation, from a maximum value to an intermediate value greater than zero. The modulating may comprise using a modulating element. The modulating element may be configured for e.g. mechanically modulating the optical radiation, e.g. by using a rotating chopper wheel, and/or for electronically modulating the optical radiation, e.g. by using an electrooptic effect and/or an acoustoptic effect, e.g. by using a Pockels cell and/or a Kerr cell.

[0157] The spectrometer 110 comprises at least one photodetector 122 according to any one of the embodiments disclosed above or below in further detail referring to the photodetector 122. An exemplary embodiment of the photodetector 122 is also schematically shown in FIG. 2 in an isolated fashion. Thus, with respect to the photodetector 122, FIGS. 1 and 2 can be described in conjunction. Generally, the photodetector 122 is a specific type of a detector 124. The detector 124 may be a measurement device, such as a sensor, configured for generating at least one measurement signal. The detector 124 may be configured for sensing or detecting or monitoring at least one physical quantity. The detector 124 may be an electronic device or an optoelectronic device. The detector 124 may be configured for generating at least one electronic signal, such as a current or a voltage or a resistance. The detector 124 may be or comprise at least one photodetector 122. As already indicated, a plurality of types of detectors 124 are in principal conceivable in the context of the present invention. However, for illustration, the focus will be on the photodetector 122 in the following.

[0158] The photodetector 122 may be an optical detector or optical sensor configured for detecting the optical radiation 112, such as for detecting an illumination and/or a light spot generated by the at least one light beam 118. The photodetector 122 is configured for performing the method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas according to any one of the embodiments disclosed above or below in further detail referring to a method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas and/or for performing the method for determining at least one item of information on the measurement object 114 according to any one of the embodiments disclosed above or below in further detail referring to a method for determining at least one item of information on the measurement object 114. The photodetector 122 comprises at least one photosensitive region 126. The photosensitive region 126 may be a unit of the photodetector 122 configured for being illuminated, or in other words for receiving the optical radiation 112, and for generating at least one signal, such as an electronic signal, in response to the optical radiation 112. The photosensitive region 126 may be located on a surface of the photodetector 122. The photosensitive region 126 may specifically be a single, closed, uniform photosensitive region 126. The photosensitive region 126 may also be referred to as pixel P. The photodetector 126 may be configured for detecting the optical radiation 112 in a wavelength of 300 nm to 3000 nm, specifically 500 nm to 2500 nm, more specifically 1400 nm to 2000 nm. The photosensitive region 126 may comprise at least one photoconductive material. The photoconductive material may be selected from at least one of PbS, PbSe, Ge, InGaAs, InSb, and HgCdTe. Photodiodes or thermopiles may also be feasible.

[0159] The spectrometer 110 may comprise at least one evaluation unit 128. The evaluation unit 128 may be configured for generating at least one item of spectral information on the measurement object 114. The evaluation unit 128 may be configured for controlling the radiation source 116. Specifically, the evaluation unit 128 may be configured for controlling a modulation frequency of the modulated radiation source 120. The photodetector 122 may comprise the evaluation unit 128 and/or at least one interface 130 for transmitting data from and/or to and/or within the evaluation unit 128. The detector 124 may comprise the evaluation unit 128 and/or at least one interface 130 for transmitting data from and/or to and/or within the evaluation unit 128. The evaluation unit 128 may at least partially be cloud based. In other words, the at least one evaluation unit 128 may at least partially be distributed in at least one cloud 132 used for at least one of cloud computing or cloud storage. The cloud 132 may specifically comprise at least one external device 134, e.g. a computer or a computer network. The cloud 132 may refer to an outsourcing of the evaluation unit 128 or of parts of the evaluation unit 128 to at least partially interconnected external devices 134, specifically computers or computer networks having larger computing power and/or data storage volume. The external devices 134 may be arbitrarily spatially distributed. The external devices 134 may vary over time, specifically on demand. The external devices 134 may be interconnected by using the internet and/or at least one intranet.

[0160] The evaluation unit 128 may be a device configured for analyzing or interpreting data, specifically for determining at least one item of qualitative or quantitative information. The information may specifically be obtained by evaluating at least one signal, such as a signal generated by the detector, specifically the measurement signal S.sub.meas. The evaluation unit 128 may be or may comprise at least one of an integrated circuit, in particular an application-specific integrated circuit (ASIC), or a data processing device, in particular at least one of a digital signal processor (DSP), a field programmable gate array (FPGA), a microcontroller, a microcomputer, a computer, or an electronic communication unit, specifically a smartphone or a tablet. Further components may be feasible, in particular at least one preprocessing device or data acquisition device. The evaluation unit 128 may comprise the interface 130 or parts thereof. The interface 130 may in particular be wireless interface and/or wire-bound. The evaluation unit 128 can be designed to, completely or partially, control or drive further devices, such as the detector 124 or the photodetector 122. The evaluation unit 128 may be designed to carry out at least one measurement cycle in which a plurality of measurement signals may be picked up. The evaluation unit 128 may be designed to control the detector 124 or the photodetector 122 for performing at least one measurement and/or for generating at least one measurement signal.

[0161] Information as determined by the evaluation unit 128 may, in particular, be provided to at least one of a further apparatus, or to a user, preferably in at least one of an electronic, visual, acoustic, or tactile fashion. The information may be stored in at least one data storage unit, specifically in an internal data storage unit as comprised by the photodetector 122 or the detector 124, in particular by the at least one evaluation unit 128, or in an separate storage unit to which the information may be transmitted via the at least one interface 130. The separate storage unit may be comprised by the at least one electronic communication unit. The storage unit may in particular be configured for storing at least one electronic table, such as at least one look-up table.

[0162] The evaluation unit 128 may be configured to perform at least one computer program, in particular at least one computer program performing or supporting the step of generating the at information. By way of example, one or more algorithms may be implemented which, by using the at least one measurement signal as at least one input variable, may perform a transformation into a piece of information. For this purpose, the evaluation unit 128 may comprise at least one data processing device, in particular at least one of an electronic or an optical data processing device, which can be designed to generate the information by evaluating the at least one measurement signal. The evaluation unit 128 may be designed to use at least one measurement signal as at least one input variable and to generate the information by processing the at least one input variable. The processing can be performed in a consecutive, a parallel, or a combined manner. The evaluation unit 128 may use an arbitrary process for generating the information, in particular by calculation and/or using at least one stored and/or known relationship.

[0163] The interface 130 may be an item or element forming a boundary configured for transferring information. The interface 130 may specifically be a communication interface. In particular, the interface 130 may be configured for transferring information from a computational device, e.g. a computer, such as to send or output information, e.g. onto another device. Additionally or alternatively, the interface 130 may be configured for transferring information onto a computational device, e.g. onto a computer, such as to receive information. The interface 130 may specifically provide means for transferring or exchanging information. In particular, the interface 130 may provide a data transfer connection, e.g. Bluetooth, NFC, inductive coupling or the like. As an example, the interface 130 may be or may comprise at least one port comprising one or more of a network or internet port, a USB-port and a disk drive. The interface 130 may comprise at least one web interface.

[0164] The spectrometer 110 may comprise at least one optical filter element 136. The optical filter element 136 may be configured for filtering the optical radiation 112 or more specifically selected wavelengths of the optical radiation 112. The at least one filter element 136 may specifically be positioned in a beam path before at least one photosensitive region 126 of the photodetector 122. The spectrometer may comprise a plurality of photosensitive regions 126 and a plurality of optical filter elements 136, wherein at least one optical filter element 136 may be positioned in a beam path before at least one photosensitive region 126, wherein the plurality of optical filter elements 136 may be configured for at least partially filtering different wavelengths. The photodetector 122 may comprise at least one readout circuit 138. The readout circuit 138 may be configured for reading out at least one signal generated by the photosensitive region 126. The readout circuit 138 may be connected to further components of the photodetector 122, such as to at least one of the evaluation unit 128 or the interface 130, e.g. by using at least one wire 140 or at least one trace 142. The spectrometer 110 may comprise at least one housing 144 surrounding at least parts of the spectrometer 110, such as at least one of the radiation source 116 and the photodetector 122. The at least one external device 134 of cloud 132 may be arranged outside of the housing 144. The housing 144 may comprise at least one window 146. The window 146 may at least partially be transparent for the optical radiation 112.

[0165] In the following, an exemplary beam path of the optical radiation 112 is described with respect to FIG. 1. The at least one radiation emitting element 116 may emit the optical radiation 112 as incident optical radiation 148 through the window 146 towards the measurement object 114. The measurement object 114 may at least partially, specifically diffusely, reflect the incident optical radiation 148 towards the at least one photosensitive region 126 of the photodetector 122 in form of reflected optical radiation 150. The measurement object 114 may at least partially absorb the incident optical radiation 148, which may be indicative of at least one physical property or chemical composition of the measurement object 114. The reflected optical radiation 150 may pass the window 146 and the optical filter element 136 before reaching the photosensitive region 126. The photosensitive region 126 may generate a corresponding measurement signal S.sub.meas which may for instance be read out by using the readout circuit 138.

[0166] As already indicated, FIG. 2 schematically shows an exemplary embodiment of the photodetector 122 according to the present invention. For a description of the photodetector 122, it may largely be referred to the description of the spectrometer 110 above. As said, the photodetector 122 is configured for performing the method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas according to any one of the embodiments disclosed above or below in further detail referring to a method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas and/or for performing the method for determining at least one item of information on the measurement object 114 according to any one of the embodiments disclosed above or below in further detail referring to a method for determining at least one item of information on the measurement object 114.

[0167] FIG. 3 shows a flow chart of an exemplary embodiment of a method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas of the detector 124. The measurement signal S.sub.meas comprises the AC signal S.sub.AC and at least one direct current (DC) signal S.sub.DC. The AC signal S.sub.AC has at least one predefined frequency f.sub.0. The method comprising the following steps: [0168] a) (denoted with reference number 152) monitoring the measurement signal S.sub.meas over time by using the detector 124; [0169] b) (denoted with reference number 154) determining the DC signal S.sub.DC by using at least one evaluation unit 128, wherein the determining comprises evaluating the measurement signal S.sub.meas by using at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0; and [0170] c) (denoted with reference number 156) determining the AC signal S.sub.AC by subtracting the DC signal S.sub.DC from the measurement signal S.sub.meas by using the evaluation unit 128.

[0171] The method steps may be performed in the indicated order. It shall be noted, however, that a different order is also possible. The method may comprise further method steps which are not listed herein. Further, one or more of the method steps may be performed once or repeatedly. Further, two or more of the method steps may be performed simultaneously or in a timely overlapping fashion. The method steps may at least partially be computer-implemented. As indicated, the detector 124 may comprise the photodetector 122 comprising at least one photosensitive region 126. Step a) may comprise measuring the measurement signal S.sub.meas by using the photosensitive region 126 of the photodetector 122. The measurement signal S.sub.meas may be dependent on an illumination of the photosensitive region 126.

[0172] The method may comprise correcting at least one environmental change affecting the measurement signal S.sub.meas. The environmental change may specifically comprise at least one of a temperature change, a change in a background light, a mechanical stress, and a humidity change and a degradation of at least a part of the detector. The correcting may be a compensating or a readjusting of an entity. The correcting may comprise removing or eliminating perturbations, specifically external perturbations, affecting the measurement signal S.sub.meas. Specifically, the correcting may comprise removing a contribution to the measurement signal S.sub.meas caused by an environmental change, such as a temperature change. Such a contribution may refer to a DC signal S.sub.DC. As said, the detector 124 may be a photodetector 122 of a spectrometer 110 configured for measuring the optical radiation 112. Other external influences besides the optical radiation 112 to be measured may not be of interest in the measurement and may only disturb the measurement signal S.sub.meas. The spectrometer 110 may further comprise a modulated radiation source 120. Thus, the signal of interest may be an AC signal S.sub.AC. External influences, e.g. temperature, may typically change on larger time scales compared to the AC signal S.sub.AC and may be one-directional at least in the monitored period of time. The external influences may typically contribute in form of a DC signal S.sub.DC to the measurement signal S.sub.meas. Identifying the DC signal S.sub.DC in the measurement signal S.sub.meas and removing the DC signal S.sub.DC from the measurement signal S.sub.meas may thus lead to the AC signal S.sub.AC which may be of particular interest in the measurement.

[0173] The retrieving may be at least one of a determining, a deriving and a filtering out a signal or at least a part of the signal. As said, the measurement signal S.sub.meas comprises the AC signal S.sub.AC and the DC signal S.sub.DC. The retrieving may comprise identifying and/or isolating the AC signal S.sub.AC in the measurement signal S.sub.meas. The retrieving may comprise removing and/or eliminating the DC signal S.sub.DC from the measurement signal S.sub.meas. The retrieving may comprise providing the AC signal S.sub.AC to further entities for further processing and/or evaluation, such as for determining an item of information, e.g. on the measurement object 114.

[0174] The signal may be an observable change in at least one physical quantity. The signal may be or comprise a sign or a function conveying information about the at least one physical quantity. The signal may specifically be or comprise at least one of an electronic signal, an optical signal or an optoelectronic signal. The signal may be a variable signal, specifically over time. The signal may be an analog signal. The signal may be or comprise at least one of a variable voltage, a variable current, a variable charge, a variable resistance or, generally, a variable electromagnetic wave. The variable electromagnetic wave may comprise at least one of a variable amplitude, a variable frequency or a variable phase. The signal may be a digital signal. The signal may comprise at least one count. The signal may specifically be related to at least one measurement. The signal may specifically be generated by the detector 124.

[0175] The measurement signal may be a signal relating to at least one measurement, more specifically to the measurement object 114. The measurement signal may be a signal generated by the detector 124 upon detection of at least one physical quantity, such as a physical quantity of the measurement object 114. The measurement signal may comprise at least one electronic signal, such as a current or a voltage or a resistance. The measurement signal may comprise an analog signal. The measurement signal may comprise a digital signal, such as a count. The measurement signal may be a superposition of two or more signals or sub-signals. The measurement may be affected by plurality of influences, such as illumination, temperature, humidity or mechanical stress. Each influence may contribute to the measurement signal. The measurement signal may be dividable into two or more sub-signals, wherein the sub-signals may at least partially relate to different influences.

[0176] The DC signal S.sub.DC may be a one-directional or at least essentially one-directional signal over time, such as a continuously increasing signal over time or a continuously decreasing signal over time. As an example, the DC signal S.sub.DC may be a digital signal, wherein a count may continuously increases over time. The DC signal S.sub.DC may comprise at least one plateau over the course of time. Deviations from a strictly one-directional progression may e.g. arise due to signal noise or external perturbations.

[0177] The AC signal S.sub.AC may be a signal which over time reverses direction and/or changes its magnitude, e.g. periodically. As an example, the AC signal S.sub.AC may be a digital signal, wherein a count increases and decreases over time in an alternating fashion. The AC signal S.sub.AC may be a sinusoidal signal, a square wave, a pulse-width modulated signal, or a combination of the previously mentioned ones. The AC signal S.sub.AC may be a periodic signal or an at least essentially periodic signal. Deviations from a strictly periodic progression may e.g. arise due to signal noise or external perturbations. As said, the AC signal S.sub.AC has at least one predefined frequency f.sub.0. The frequency may generally be a number of occurrences of a repeating event over time. The frequency can be defined as a reciprocal of a period duration, such as a period duration of a periodic signal. The frequency may be predefined by at least one default, such as at least one default in a measurement setup. A user may be allowed to set the default or to choose between a number of different available defaults. As said, the detector 124 may be a photodetector 122 of a spectrometer 110, wherein the spectrometer 110 may further comprise the modulated radiation source 120. Thus, the frequency of the AC signal S.sub.AC may be predefined by setting a specific modulation frequency at the modulated radiation source 120. An overtone may be a harmonic of a fundamental frequency, such as of the frequency f.sub.0. An overtone of the frequency f.sub.0 may be a positive integer multiple of the frequency f.sub.0, such as 2 f.sub.0, 3 f.sub.0, 4 f.sub.0 and so on.

[0178] Step a) comprises monitoring the measurement signal S.sub.meas over time by using the detector 124. The monitoring over time may be at least one of measuring, observing or recording an entity, such as the measurement signal S.sub.meas, specifically over time. The monitoring may comprise recording a progression and/or a development of the measurement signal S.sub.meas over time.

[0179] Step b) comprises determining the DC signal S.sub.DC by using the evaluation unit 128, wherein the determining comprises evaluating the measurement signal S.sub.meas by using at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0. The evaluating may be a processing or an analyzing or an interpreting of an entity, such as of the measurement signal S.sub.meas. The evaluating may comprise performing at least one mathematical calculation involving the measurement signal S.sub.meas. The evaluating may comprise transforming and/or converting the measurement signal S.sub.meas. The evaluating may comprise using at least one relationship, such as a predefined and/or predetermined relationship, e.g. from a look-up table, or a variable relationship, such as function. The evaluating may comprise filtering and/or smoothening the measurement signal S.sub.meas. The evaluating may comprise deriving at least one qualitative or quantitative item of information from the measurement signal S.sub.meas, such as a contribution of the DC signal S.sub.DC and/or the AC signal S.sub.AC to the measurement signal S.sub.meas. Different approaches may be possible for such purpose as will be outlined in further detail below.

[0180] Step c) comprises determining the AC signal S.sub.AC by subtracting the DC signal S.sub.DC from the measurement signal S.sub.meas by using the evaluation unit. The subtracting may be one or more of removing, eliminating and deducting the DC signal S.sub.DC from the measurement signal S.sub.meas, specifically over an entire period of time. The subtracting may comprise extracting the AC signal S.sub.AC from the measurement signal S.sub.meas. The subtracting may comprise at least one mathematical calculation. The subtracting may comprise subtracting the DC signal S.sub.DC, such as a count of the DC signal S.sub.DC, from the measurement signal S.sub.meas, such as from a count of the measurement signal S.sub.meas, specifically for each point in time individually over the entire period of time. In such way, the AC signal S.sub.AC may for instance be determined for each point in time, thus for each chosen time unit, e.g. for each millisecond or for each frame number of the photodetector 122.

[0181] FIGS. 4-6B show experimental results of measurements on an exemplary embodiment of a spectrometer 110 according to the present invention. FIG. 4 shows a first approach for determining the DC signal S.sub.DC in step b), wherein signals S are counted over frames F. A raw measurement signal is denoted with reference number 158. A masked measurement signal is denoted with reference number 160. In FIG. 4, the masked measurement signal 160 masks times when the AC signal S.sub.AC reaches local minima, specifically based on at least one of the frequency f.sub.0, at least one overtone of the frequency f.sub.0 and a phase . The DC signal S.sub.DC may be determined by using a phase of the measurement signal S.sub.meas, specifically of the AC signal S.sub.AC, specifically besides the frequency f.sub.0. The evaluation of the measurement signal S.sub.meas may comprise determining local minima of the measurement signal S.sub.meas by using the frequency f.sub.0 and the phase and at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0. The DC signal S.sub.DC may be determined by using the local minima. The phase may be a position indicator within a periodic signal. Typically, the phase may be represented as an angle. The phase may be dependent on the time, on a frequency of the signal and/or on a phase offset. Specifically, the phase may indicate when a periodic signal or a periodic part of a total signal, such as a periodic sub-signal, reaches an extremum, such as a minimum or a maximum. As an example, the measurement signal S.sub.meas may show an at least essentially periodic sub-signal, e.g. due to using a modulated radiation source as already outlined. This sub-signal may correspond to the AC signal S.sub.AC which may be of interest in the end, but which at this stage may drift e.g. due to an environmental change. The frequency f.sub.0 and the phase of this sub-signal may be used for identifying minima in the sub-signal, which may simultaneously at least be local minima in the overall measurement signal S.sub.meas. The local minimum may be a lowest signal value in a signal interval, specifically within a period of a periodic signal. The signal may comprise a plurality of local minima. The local minima may at least partially have the same level. The local minima may specifically at least partially have different levels, specifically due to external perturbations, such as an environmental change affecting the detector and/or the measurement signal. The measurement signal S.sub.meas may specifically be recorded in counts over time. As said, the measurement signal comprises the AC signal S.sub.AC and the DC signal S.sub.DC. A local minimum may be a lowest count in a time interval relating to a period of the AC signal S.sub.AC.

[0182] The evaluation of the measurement signal S.sub.meas may comprise fitting the DC signal S.sub.DC to the local minima of the measurement signal S.sub.meas. The DC signal S.sub.DC may be a function S.sub.DC(t) over time comprising at least one of a polynomial function having at least one fit parameter, an exponential function having at least one fit parameter, a square root function having at least one fit parameter and a logarithmic function having at least one fit parameter. The fitting may comprise a regression analysis for estimating a relation between at least two variables. The fitting may comprise at least one of a linear regression, a partial least square regression, a non-linear regression, an interpolation and an extrapolation. The fitting may comprise at least one regression model, e.g. a trained model. The fitting may comprise using at least one fit function, such as at least one of the functions listed above. The function S.sub.DC(t) may be a fit function fitted to the local minima of the measurement signal S.sub.meas. The fit function may comprise at least one fit parameter. The fit parameter may be a parameter or a coefficient of a fit function. As an example, the fit function may be a linear function and the fit parameters may be a slope and an offset of the linear function.

[0183] As specifically shown in FIG. 4, a 4.sup.th order polynomial function may be fitted to the masked measurement signal 160. The fitted baseline is denoted with reference number 162. The fitted baseline 162 may be subtracted from the raw measurement signal 158 for determining the AC signal S.sub.AC. The in such way obtained corrected measurement signal based on the masked measurement signal is denoted with reference sign 164. Additionally or alternatively, as will be outlined in further detail below, the measurement signal may be corrected by using frequency filtering. The in such way obtained corrected measurement signal by using frequency filtering is denoted with reference sign 166. As FIG. 4 indicates, both approaches show comparable performance.

[0184] FIGS. 5A and 5B show a further approach for determining the DC signal S.sub.DC in step b). Additionally or alternatively to the above-described approach using the local minima of the measurement signal S.sub.meas, in step b) the DC signal S.sub.DC may be determined by transforming the measurement signal S.sub.meas into a frequency domain. The frequency domain may refer to an analysis of a signal with respect to at least one frequency of the signal. A signal may typically be recorded over time in the time domain meaning that a signal value is related to a specific point in time. However, for a variety of applications, it may be helpful to analyze the signal with respect to frequencies comprised by the signal in the frequency domain. As an example, one total signal may comprise a plurality of sub-signals each comprising a specific frequency. The sub-signals may be distinguishable, e.g. for further isolated processing, by analyzing the frequencies in the total signal. In the frequency domain, a signal value may be related to a specific frequency. Signal values, such as signal values of a total signal, may be plotted over a frequency interval in the frequency domain.

[0185] The measurement signal S.sub.meas may be transformed into the frequency domain by using a Fourier transformation. FIG. 5A shows such Fourier transformed signals obtained by using fast Fourier transformation (FFT), wherein the absolute signal counts are plotted on a logarithmic scale over the corresponding frequency f. The Fourier transformed raw measurement signal is denoted with reference number 168. The frequency f.sub.0 and the first overtone at 2 f.sub.0 are recognizable as peaks at approximately 15 Hz and 30 Hz, respectively. A distortion approximation is fitted to the Fourier transformed raw measurement signal 168 in FIG. 5A and is denoted with reference number 170. Further, a noise floor is denoted with reference number 172. The Fourier transformation may be an integral transformation for decomposing an integratable function depending on space or time into a function depending on spatial frequency or temporal frequency. Specifically, the Fourier transformation may be configured for decomposing a time dependent signal into a frequency dependent signal. The Fourier transformation may comprise at least one of a Fourier analysis, a continuous Fourier transformation, a discrete Fourier transformation and a Fourier related transformation, such as a Laplace transformation for instance. In step b), the DC signal S.sub.DC may specifically be determined by setting at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0 to zero in the frequency domain before retransformation into the time domain, such as by using an inverse Fourier transformation. Thus, step c) may specifically be performed in the time domain again.

[0186] The evaluation of the measurement signal S.sub.meas, such as performed in step b), may comprise filtering the transformed measurement signal S.sub.meas for at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0. The filtering may be a selectively extracting at least one part of a signal, such as a specific signal interval, e.g. in the frequency domain. The filtering may comprise extracting specific frequencies, or sub-signals having specific frequencies, out of a total signal in the frequency domain. Specifically, the filtering may comprise extracting the at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0 from the measurement signal S.sub.meas. The rest of the original measurement signal S.sub.meas may stay as a remainder. The frequency f.sub.0 and overtones of the frequency f.sub.0 may refer to the AC signal S.sub.AC. The remainder may refer to the DC signal S.sub.DC. The filtering may comprise using at least one electronic filter element, specifically at least one frequency electronic filter element, such as an electronic bandpass filter element. The electronic filter element may be an analog electronic filter element or a digital electronic filter element.

[0187] The evaluation of the measurement signal S.sub.meas may comprise using the filtered transformed measurement signal S.sub.meas for determining the DC signal S.sub.DC. Specifically, the evaluation of the measurement signal S.sub.meas may comprise using a remainder of the filtering of the transformed measurement signal S.sub.meas for determining the DC signal S.sub.DC The evaluation of the measurement signal S.sub.meas may comprise fitting the DC signal S.sub.DC to the filtered transformed measurement signal S.sub.meas, specifically to the remainder of the filtering of the transformed measurement signal S.sub.meas. The DC signal S.sub.DC may be a function S.sub.DC(t) over time comprising at least one of a polynomial function having at least one fit parameter, an exponential function having at least one fit parameter, a square root function having at least one fit parameter and a logarithmic function having at least one fit parameter. The DC signal S.sub.DC may carry a non-zero power at at least one of the frequency f.sub.0 and at least one overtone of the frequency f.sub.0. FIG. 5B shows signals S counted over frames F in the time domain. A raw measurement signal is denoted with reference number 174. A filtered measurement signal, wherein a carrier frequency and overtones are filtered out, is denoted with reference number 176. A fitted correction is denoted with reference number 178 and a corrected measurement signal is denoted with reference number 180.

[0188] FIGS. 6A and 6B show applications of the method for retrieving at least one alternating current (AC) signal S.sub.AC from at least one measurement signal S.sub.meas for different conditions. FIG. 6A shows a correction of a signal S for the case S.sub.DC<<S.sub.AC for 250 pixels P. A raw fast Fourier transformed (FFT) measurement signal is denoted with reference number 182. A corrected fast Fourier transformed (FFT) measurement signal is denoted with reference number 184. FIG. 6B shows a correction of a signal S for the cases S.sub.DCS.sub.AC or S.sub.DC>>S.sub.AC for 250 pixels P. A raw fast Fourier transformed (FFT) measurement signal is denoted with reference number 186. A corrected fast Fourier transformed (FFT) measurement signal is denoted with reference number 188. For all conditions, a clear signal recovery is evident.

[0189] FIG. 7 shows a flow chart of an exemplary embodiment of a method for determining at least one item of information on the measurement object 114 by using the detector 124. The method comprises the following steps: [0190] i) (denoted with reference number 190) determining at least one measurement signal S.sub.meas by using the detector 124; [0191] ii) (denoted with reference number 192) determining the AC signal S.sub.AC by using a method according to any one of the embodiments disclosed above or below in further detail referring to a method for retrieving at least one AC signal S.sub.AC from at least one measurement signal S.sub.meas; and [0192] iii) (denoted with reference number 194) determining the item of information on the measurement object 114 by evaluating the AC signal S.sub.AC by using the evaluation unit 128.

[0193] The method steps may be performed in the indicated order. It shall be noted, however, that a different order is also possible. The method may comprise further method steps which are not listed herein. Further, one or more of the method steps may be performed once or repeatedly. Further, two or more of the method steps may be performed simultaneously or in a timely overlapping fashion. The method steps may at least partially be computer-implemented. The item of information may be knowledge or evidence providing a qualitative and/or quantitative description relating to at least one measurement, specifically to the at least one measurement object 114. The item of information may comprise at least one of a physical property of the measurement 114 object or a chemical composition of the at least one measurement object 114. The physical property may specifically comprise an optical property such at least one absorbance of the measurement object 114 and/or at least one emissivity of the measurement object 114. The chemical composition may specifically refer to qualitative and/or quantitative information on at least one material the measurement object 114 comprises.

LIST OF REFERENCE NUMBERS

[0194] 110 spectrometer [0195] 112 optical radiation [0196] 114 measurement object [0197] 116 radiation source [0198] 118 light beam [0199] 120 modulated radiation source [0200] 122 photodetector [0201] 124 detector [0202] 126 photosensitive region [0203] 128 evaluation unit [0204] 130 interface [0205] 132 cloud [0206] 134 external device [0207] 136 optical filter element [0208] 138 readout circuit [0209] 140 wire [0210] 142 trace [0211] 144 housing [0212] 146 window [0213] 148 incident optical radiation [0214] 150 reflected optical radiation [0215] 152 method step a) [0216] 154 method step b) [0217] 156 method step c) [0218] 158 raw measurement signal [0219] 160 masked measurement signal [0220] 162 fitted baseline [0221] 164 corrected measurement signal based on the masked measurement signal [0222] 166 corrected measurement signal based on using frequency filtering [0223] 168 Fourier transformed raw measurement signal [0224] 170 distortion approximation [0225] 172 noise floor [0226] 174 raw measurement signal [0227] 176 filtered measurement signal [0228] 178 fitted correction [0229] 180 corrected measurement signal [0230] 182 raw fast Fourier transformed (FFT) measurement signal [0231] 184 corrected fast Fourier transformed (FFT) measurement signal [0232] 186 raw fast Fourier transformed (FFT) measurement signal [0233] 188 corrected fast Fourier transformed (FFT) measurement signal [0234] 190 method step i) [0235] 192 method step ii) [0236] 194 method step iii)