METHOD AND DEVICE FOR MONITORING RADIATION

Abstract

Described herein is a method and a device for monitoring radiation emitted by a radiation emitting element of a thermal radiation source within the visible and the infrared spectral ranges, specifically for determining an emission spectrum of the thermal radiation source. The method includes the following steps: a) providing a thermal radiation source including a radiation emitting element; b) providing at least one radiation sensitive element; c) measuring a spectral radiance of the radiation emitted by the radiation emitting element at at least two individual wavelengths; and d) determining an emission temperature of the radiation emitting element by providing a ratio of the measured values of the spectral radiance of the radiation at the at least two individual wavelengths.

Claims

1. A method for monitoring radiation emitted by a radiation emitting element of a thermal radiation source, wherein the method comprises the following steps: a) providing a thermal radiation source comprising a radiation emitting element, wherein the radiation emitting element emits radiation to be monitored, wherein the radiation emitting element comprises a wire filament of an incandescent lamp or a radiation emitting surface of a thermal infrared emitter; b) providing at least one radiation sensitive element, wherein the radiation sensitive element is designated for measuring the radiation emitted by the radiation emitting element; c) measuring a spectral radiance of the radiation emitted by the radiation emitting element at at least two individual wavelengths; and d) determining an emission temperature of the radiation emitting element by providing a ratio of the measured values of the spectral radiance of the radiation at the at least two individual wavelengths, wherein the ratio of the measured values of the spectral radiance for the two of the individual wavelengths as a function of temperature is approximated by using a polynomial function of second order within a temperature range from 1000 K to 4000 K.

2. The method according to claim 1, wherein the spectral radiance of the radiation at the at least two individual wavelengths is evaluated by using Planck's law which provides a relationship between the spectral radiance of the radiation emitted by the radiation emitting element and the emission temperature of the radiation emitting element.

3. The method according to claim 1, wherein the emission temperature of the radiation emitting element is determined by comparing measured values for the spectral radiance at at least two of the individual wavelengths.

4. The method according to claim 3, wherein the ratio of the measured values of the spectral radiance for two of the individual wavelengths is a quotient of the measured values of the spectral radiance for the two individual wavelengths.

5. The method according to claim 1, wherein a first wavelength at which the spectral radiance is measured is selected from the group consisting of the visual spectral range, and wherein a second wavelength at which the spectral radiance is measured is selected from the group consisting of the near infrared spectral range.

6. The method according to claim 1, 1 wherein a relative spectral sensitivity of the radiation sensitive element at the at least two individual wavelengths is further taken into account when evaluating the spectral radiance of the radiation at the at least two individual wavelengths.

7. The method according to claim 1, wherein the spectral radiance of the radiation emitted by the radiation emitting element is measured at a single wavelength, wherein the emission temperature of the radiation emitting element is determined by comparing a measured value of the spectral radiance for the single wavelength with a known value of the spectral radiance for the single wavelength, wherein the known value for the spectral radiance is obtained in a calibration of the radiation sensitive element.

8. The method according to claim 7, wherein a known thermal radiation source having a known emission temperature of the radiation emitting element is used for the calibration of the radiation sensitive element, wherein the measuring of the spectral radiance of the radiation emitted by the radiation emitting element is performed in a same controlled environment in which the calibration of the radiation sensitive element is performed.

9. A computer program product which comprises executable instructions for performing the method according to claim 1.

10. A device for monitoring radiation emitted by a radiation emitting element of a thermal radiation source, wherein the radiation emitting element comprises a wire filament of an incandescent lamp or a radiation emitting surface of a thermal infrared emitter, wherein the device comprises: at least one radiation sensitive element, wherein the radiation sensitive element is designated for measuring radiation which is emitted by the radiation emitting element of the thermal radiation source at at least two individual wavelengths; and an evaluation device, wherein the evaluation device is designated for determining an emission temperature of the radiation emitting element by providing a ratio of the measured values of the spectral radiance of the radiation at the at least two individual wavelengths, wherein the ratio of the measured values of the spectral radiance for the two of the individual wavelengths as a function of temperature is approximated by using a polynomial function of second order within a temperature range from 1000 K to 4000 K.

11. The device according to claim 10, wherein the evaluation device is designated for evaluating the spectral radiance of the radiation at the at least one wavelength by using Planck's law which provides a relationship between the spectral radiance of the radiation emitted by the radiation emitting element and the emission temperature of the radiation emitting element.

12. The device according to claim 10, wherein the radiation sensitive element comprises a radiation sensor having at least one sensor region, wherein the sensor region comprises a radiation sensitive material, wherein the radiation sensitive material is selected from the group consisting of silicon, indium gallium arsenide (InGaAs), indium arsenide (InAs), lead sulfide (PbS), lead selenide (PbSe), indium antimonide (InSb), and mercury cadmium telluride (MCT, HgCdTe).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0114] Further optional details and features of the invention are evident from the description of preferred exemplary embodiments which follows in conjunction with the dependent claims. In this context, the particular features may be implemented alone or with features in combination. The invention is not restricted to the exemplary embodiments. The exemplary embodiments are shown schematically in the figures. Identical reference numerals in the individual figures refer to identical elements or elements with identical function, or elements which correspond to one another with regard to their functions.

[0115] Specifically, in the figures:

[0116] FIG. 1 illustrates a preferred exemplary embodiment of a device for monitoring radiation emitted by a radiation emitting element of a thermal radiation source according to the present invention;

[0117] FIG. 2 illustrates a further preferred exemplary embodiment of the device for monitoring the radiation emitted by the radiation emitting element of the thermal radiation source according to the present invention;

[0118] FIG. 3 illustrates a diagram indicating a preferred exemplary embodiment of a method for monitoring the radiation emitted by the radiation emitting element of the thermal radiation source according to the present invention; and

[0119] FIG. 4 illustrates experimental results for a quotient of two values for a spectral radiance measured for two different wavelengths versus an emission temperature of the radiation emitting element.

EXEMPLARY EMBODIMENTS

[0120] FIG. 1 illustrates, in a highly schematic fashion, an exemplary embodiment of device 110 for monitoring radiation 112 emitted by a radiation emitting element of a thermal radiation source according to the present invention. Without limiting the scope of the present invention, a wire filament 114 of an incandescent lamp 116 is used in the following examples as the radiation emitting element, wherein the incandescent lamp 116 is the selected as the thermal radiation source for this purpose. As an alternative, other kinds of thermal radiation sources, especially a thermal infrared emitter as described above in more detail, may also be used as the thermal radiation source in a similar fashion within the exemplary embodiments of FIGS. 1 to 4.

[0121] As schematically depicted in FIG. 1, the incandescent lamp 116 comprises a bulb 118, in particular of glass or fused quartz, wherein the wire filament 114, which may, specifically, comprise tungsten, is located in a volume 120, preferably filled with inert gas or comprising a vacuum, carried by a carrier 122. For a purpose of the generating the desired radiation 112, the wire filament 114 is impinged by an electrical current in a fashion that a heating of the wire filament 114 results in an emission of photons over a considerably wide spectral range, specifically the visible spectral range and, in particular, the near infrared (NIR) spectral range. As generally used, the visible spectral range covers wavelengths of 380 nm to 780 nm while the NIR spectral range covers wavelengths of 780 nm to 1400 nm.

[0122] As further illustrated in FIG. 1, the device 110 according to the present invention comprises a radiation sensitive element 124 which is designated for measuring the radiation 112 that is emitted by the wire filament 114 of the incandescent lamp 116 at one or more wavelengths. In the particular embodiment of FIG. 1, the radiation sensitive element 124 is a radiation sensor 126 which comprises a uniform sensor region 128, wherein the sensor region 128 is designated for receiving the illumination of the radiation sensor 126 by the radiation 112 being generated by the wire filament 114 in a manner that a generation of at least one sensor signal may be triggered. Herein, the generation of the sensor signal may be governed by a defined relationship between the sensor signal and the manner of the illumination of the sensor region 128. Herein, the sensor region 128 may have a size of 10 mm×10 mm or less, preferred of 5 mm×5 mm or less, more preferred of 2 mm×2 mm or less.

[0123] For a purpose of generating the at least one sensor signal upon illumination, the sensor region 128 comprises a radiation sensitive material which may, preferably be selected from silicon, in particular for incident wavelengths up to 1 μm. For incident wavelengths above 1 μm, the radiation sensitive material may, alternatively, be selected from indium gallium arsenide (InGaAs), in particular for incident wavelengths up to 2.6 μm; indium arsenide (InAs), in particular for incident wavelengths up to 3.1 μm; lead sulfide (PbS), in particular for incident wavelengths up to 3.5 μm; lead selenide (PbSe), in particular for incident wavelengths up to 5 μm; indium antimonide (InSb), in particular for incident wavelengths up to 5.5 μm; and mercury cadmium telluride (MCT, HgCdTe), in particular for incident wavelengths up 16 μm. However, further kinds of materials may also be conceivable.

[0124] As described above and below in more detail, the radiation 112 being generated by the wire filament 114 is, preferably, measured at two different wavelengths. For this purpose, the radiation sensitive element 124 as depicted in FIG. 1 is, particularly, selected to be sensitive for the different wavelengths. As an alternative, the radiation sensor 126 may comprise two or more individual uniform sensor regions 128, wherein each of the individual uniform sensor regions 128 may be sensitive to a particular wavelength. As a preferred example, the individual sensor regions 128 may exhibit a high spectral sensitivity between 500 nm and 600 nm, such as around 550 nm, and between 800 nm and 1000 nm, such as around 900 nm, respectively. Herein, a differing spectral sensitivity of the radiation sensitive element 124 at the two different wavelengths can, preferably, be taken into account when evaluating the radiation 112 being measured by the sensor region 128 at the two different wavelengths.

[0125] As further illustrated in FIG. 1, the device 110 according to the present invention comprises an evaluation device 130 which is designated for determining an emission temperature T of the wire filament 114 of the incandescent lamp 116 by evaluating a spectral radiance of the radiation 112 at the one or, preferably, more selected wavelengths. For this purpose, the at least one sensor signal as generated by the radiation sensitive element 124 is transferred to the evaluation device 130 by an interface 132, such as a wireless interfaces and/or a wire-bound interface. Further, the evaluation device 130 may comprise a processing device 134, such as a computer, preferably a microcomputer or a microcontroller, which may, be designated for performing the method according to the present invention, in particular by generating a computer program product which comprises executable instructions for performing the method. Further, the evaluation device 130 may be connected to a monitor 136 and/or a keyboard 138 which may, preferably, be located outside the device 110. However, other embodiments of the evaluation device 130 may also be conceivable.

[0126] In a particular embodiment, the radiation sensitive element 124 and the evaluation device 130 as well as the monitor 136 and the tablet 138 may be comprised by an electronic device (not depicted here), in particular an electronic communication unit, such as a smartphone or a tablet. Herein, the smartphone may be capable of performing the method according to the present invention by using one or more radiation sensitive elements which are already comprised by the smartphone for a use of a camera and/or for display control and by using a data processing device which is already also comprised by the smartphone for various purposes as well as by using the display of the smartphone as monitor and keyboard. In this respect, the method may be performed as an application, also denoted by the abbreviation of “app”, on the smartphone for the purposes of the present invention.

[0127] FIG. 2 illustrates, in a highly schematic fashion, a further preferred exemplary embodiment of the device 110 according to the present invention. In this embodiment, a spectrometer device 140 comprises the device 110 of the present invention in an integrated fashion, wherein the radiation sensitive element 124 may comprise a radiation sensitive array 142 being provided by a spectrometer pixel array 144 which is already being used in the spectrometer device 140 for spectroscopic purposes. Herein, two or more radiation sensitive pixels 146 of the spectrometer pixel array 144 constitute the sensor region 128. For this purpose, in a first beam path 148, the radiation 112 as generated by the wire filament 114 is guided towards an object 150 from where it is reflected to a diffractive device 152 located, apart from the radiation sensitive pixels 146, in front of the spectrometer pixel array 144 while, in a second beam path 154, the radiation 112 as generated by the wire filament 114 is guided directly towards radiation sensitive pixels 146 that constitute the sensor region 128. As schematically depicted in FIG. 2, the radiation sensitive pixels 146 which are located at an edge 156 of the spectrometer pixel array 144 may be preferred for being used as the sensor region 128 since they allow obtaining a maximum spectral distance. However, other kinds of arrangements may also be feasible.

[0128] As further depicted in FIG. 2 for this embodiment, the evaluation device 130 as well as the monitor 136 and the tablet 138 may also be comprised by the spectrometer device 140. Herein, a data processing device as already comprised by the spectrometer device 140 may, preferably, be designated for hosting a computer program product which comprises executable instructions for performing the method in relationship with the spectrometer pixel array 144.

[0129] For further details with respect to the embodiment as schematically depicted in FIG. 2, reference may be made to the description of the embodiment as illustrated in FIG. 1 as provided above.

[0130] However, it is indicated here that, apart from the preferred exemplary embodiments of the device 110 according to the present invention as shown in FIG. 1 or 2, further embodiments of the device 110 may also be conceivable.

[0131] According to step a) of the method of the present invention, the incandescent lamp 116, such as schematically depicted in FIG. 1 or 2, which comprises the wire filament 114 which is designed for emitting the radiation 112 to be monitored is provided.

[0132] In accordance with step b) of the method of the present invention, the radiation sensitive element 124 which is designated for measuring the radiation 112 is further provided.

[0133] According to step c) of the method of the present invention, a spectral radiance B.sub.λ of the radiation 112 which is emitted by the wire filament 114 of the incandescent lamp 116 is measured at two or more wavelengths. FIG. 3 illustrates, in a highly schematic fashion, the spectral radiance B.sub.λ of the radiation 112 of wire filament 114 for the particular wavelength λ at various emission temperatures T of 3000 K, 4000 K, and 5000 K in accordance with Planck's law as defined by Equation (2) by

[00004]$\begin{array}{cc}{B}_{\lambda }\left(\lambda ,T\right)=\frac{2h{c}^2}{{\lambda }^5}.Math.\frac{1}{e^{\frac{hc}{\lambda k_{B}T}}-1},& \left(2\right)\end{array}$

wherein h is Planck's constant, c the speed of light, and k.sub.B the Boltzmann constant. Thus, Planck's law provides a relationship between the spectral radiance B.sub.λ of the radiation which is emitted by the wire filament 114 of the incandescent lamp 116 and the emission temperature T of the wire filament 114 over the ultraviolet (UV), visible (VIS) and infrared (IR) spectral ranges. Although Planck's law is based on the emission of a perfectly black body which, strictly speaking, does not exist in reality, the emission of a black surface as, for example, comprised by the wire filament 114 of the incandescent lamp 116 can be accurately approximated hereby in practice.

[0134] As a result of Equation (2), the spectral radiance B.sub.λ of the wire filament 114 depends only on the wavelength λ of the radiation and the emission temperature T of the wire filament 114, thus, allowing a determination of the emission temperature T of the wire filament 114 of the incandescent lamp 116 by evaluating the spectral radiance B.sub.λ of the radiation 112 for the one or, preferably, wavelengths λ according to step d) of the method of the present invention. Herein, a first wavelength λ.sub.1 around 550 nm and a second wavelength λ.sub.2 around 900 nm, respectively, are schematically indicated in FIG. 3 in accordance with the preferred example provided above in which the individual sensor regions 128 exhibit a high spectral sensitivity around these wavelengths λ.sub.1, λ.sub.2.

[0135] FIG. 4 illustrates, in a highly schematic fashion, experimental results which have been obtained by using the device 110 of FIG. 1 with two individual uniform sensor regions 128, wherein a first sensor region 128 was designed for measuring the spectral radiance B.sub.λ of the radiation 112 emitted by the wire filament 114 of the incandescent lamp 116 at the first wavelength λ.sub.1 of 520 nm, i.e. in the green part of the visible spectral range, and wherein a second sensor region 128 was designed for measuring the spectral radiance B.sub.λ of the radiation 112 emitted by the wire filament 114 of the incandescent lamp 116 at the second wavelength λ.sub.2 of 850 nm, i.e. in the near infrared spectral range, respectively.

[0136] As depicted in FIG. 4, the quotient

[00005]$\frac{B_{\lambda }\left({\lambda }_1,T\right)}{B_{\lambda }\left({\lambda }_2,T\right)}$

according to Equation (0.5) for λ.sub.1=520 nm and for λ.sub.2=850 nm can approximated in an accurate fashion by a polynomial function 158 according to Equation (4) as

[00006]$\begin{array}{cc}\frac{B_{\lambda }\left({\lambda }_1,T\right)}{B_{\lambda }\left({\lambda }_2,T\right)}=-9.Math.{10}^{-15}{T}^4+9.Math.{10}^{-11}{T}^3+2.Math.{10}^{-7}{T}^2+2.Math.{10}^{-4}T+0,433.& \left(4\right)\end{array}$

[0137] Moreover, the polynomial function 158 can within a temperature range of 1000 K to 4000 K be simplified into a polynomial of second order according to Equation (5) as

[00007]$\begin{array}{cc}\frac{B_{\lambda }\left({\lambda }_1,T\right)}{B_{\lambda }\left({\lambda }_2,T\right)}=1.Math.{10}^{-7}{T}^2+3.Math.{10}^{-4}T+0,168.& \left(5\right)\end{array}$

[0138] Herein, both polynomial functions according to Equations (4) and (5) are invertible and can, thus, be used as an inverted function

[00008]$T\left(\frac{B_{\lambda }\left({\lambda }_1,T\right)}{B_{\lambda }\left({\lambda }_2,T\right)}\right)$

for determining emission temperature T of the wire filament 114 of the incandescent lamp 116 from the quotient.

LIST OF REFERENCE NUMBERS

[0139] 110 device [0140] 112 radiation [0141] 114 wire filament [0142] 116 incandescent lamp [0143] 118 bulb [0144] 120 volume [0145] 122 carrier [0146] 124 radiation sensitive element [0147] 126 radiation sensor [0148] 128 sensor region [0149] 130 evaluation device [0150] 132 interface [0151] 134 processing device [0152] 136 monitor [0153] 138 keyboard [0154] 140 spectrometer device [0155] 142 radiation sensitive array [0156] 144 spectrometer pixel array [0157] 146 radiation sensitive pixel [0158] 148 first beam path [0159] 150 object [0160] 152 diffractive element [0161] 154 second beam path [0162] 156 edge [0163] 158 polynomial function