Method for determining a temperature without contact, and infrared measuring system

Abstract

A method and an infrared measuring system for determining a temperature distribution of a surface without contact includes an infrared detector array with a detector array substrate and respective pluralities of measuring pixels and reference pixels. The measuring pixels are each connected to the detector array substrate with a first thermal conductivity, are sensitive to infrared radiation, and each provide a measurement signal for determining a temperature measurement value that depends on the intensity of the incident infrared radiation. The reference pixels are each connected to the detector array substrate with a second thermal conductivity and each provide a measurement signal for determining a temperature measurement value. The reference pixels are implemented as blind pixels that are substantially insensitive to infrared radiation. The temperature measurement values of the measuring pixels are corrected by a pixel-associated temperature drift component determined with reference to the temperature measurement values of the reference pixels.

Claims

1. A method for contactlessly establishing a temperature of a surface via an infrared measurement system that includes an infrared detector array with (i) a detector array substrate, (ii) a plurality of measurement pixels, which are each connected to the detector array substrate with a first thermal conductivity, wherein the measurement pixels are sensitive to infrared radiation and each provide a first measurement signal for establishing a first temperature measurement value which is dependent on an intensity of the incident infrared radiation, and (iii) a plurality of reference pixels, which are each connected to the detector array substrate with a second thermal conductivity and which each provide a second measurement signal for establishing a second temperature measurement value, the method comprising: determining the second temperature measurement values indicated by the second measurement signals from the plurality of reference pixels using an evaluation apparatus of the infrared measurement system; determining pixel-associated temperature drift components for the plurality of reference pixels with reference to the second temperature measurement values using the evaluation apparatus; determining the first temperature measurement values indicated by the first measurement signals from the plurality of measurement pixels using the evaluation apparatus, the first temperature measurement values being indicative of a temperature of the surface; and correcting the first temperature measurement values with the pixel-associated temperature drift components using the evaluation apparatus, wherein the reference pixels are configured as blind pixels that are substantially insensitive to infrared radiation, and wherein the second thermal conductivity is greater than the first thermal conductivity.

2. The method as claimed in claim 1, wherein the temperature drift components are determined repeatedly at time intervals.

3. The method as claimed in claim 1, wherein a temperature drift behavior of the reference pixels is determined from the second temperature measurement values of the reference pixels, and wherein the temperature drift components are determined as a function of the temperature drift behavior.

4. The method as claimed in claim 3, wherein the temperature drift behavior of the reference pixels is determined as a constant of proportionality between initial measurement deviations of the reference pixels and the second temperature measurement values of the reference pixels for determining the temperature drift components.

5. The method as claimed in claim 3, wherein the temperature drift behavior of the reference pixels is determined as a constant of proportionality between sensitivities of the initial measurement deviations in relation to the influences of aging of the reference pixels and the second temperature measurement values of the reference pixels for determining the temperature drift components.

6. The method as claimed in claim 3, wherein a mathematical relationship is established between a temperature drift behavior of measurement pixels and a temperature drift behavior of reference pixels for determining the temperature drift components, and the temperature drift behavior of measurement pixels is determined from the mathematical relationship.

7. The method as claimed in claim 6, wherein the temperature drift behavior of the measurement pixels is set equal to the temperature drift behavior of the reference pixels.

8. The method as claimed in claim 6, wherein the temperature drift components are determined from the temperature drift behavior by virtue of the temperature drift components of the respective measurement pixels being calculated in the form of a function as a product of temperature drift behavior and initial measurement deviations of the respective measurement pixels.

9. The method as claimed in claim 6, wherein the temperature drift components are determined from the temperature drift behavior by virtue of the temperature drift components of the respective measurement pixels being calculated in the form of a function as a product of the temperature drift behavior and influences of aging of the respective measurement pixels.

10. The method as claimed in claim 1, further comprising: suppressing an incidence of infrared radiation onto the infrared detector array by a closure mechanism of the infrared measurement system; and correcting each of the first temperature measurement values by a pixel-dependent deviation from a mean value of the second temperature measurement values measured in the case of a suppressed incidence of infrared radiation.

11. An infrared measurement system for contactlessly establishing a temperature distribution on a surface, comprising: an evaluation apparatus; and at least one infrared detector array that includes: a detector array substrate, a plurality of measurement pixels, which are each connected to the detector array substrate with a first thermal conductivity, wherein the measurement pixels are sensitive to infrared radiation and each provide a first measurement signal configured to establish a first temperature measurement value T.sub.MP which is dependent on an intensity of the incident infrared radiation, and a plurality of reference pixels, which are each connected to the detector array substrate with a second thermal conductivity and which each provide a second measurement signal configured to establish a second temperature measurement value, wherein the reference pixels are configured as blind pixels that are substantially insensitive to infrared radiation, and wherein the second thermal conductivity is greater than the first thermal conductivity, wherein the evaluation apparatus is configured to: determine the second temperature measurement values indicated by the second measurement signals from the plurality of reference pixels, determine pixel-associated temperature drift components for the plurality of reference pixels with reference to the second temperature measurement values, determine the first temperature measurement values indicated by the first measurement signals from the plurality of measurement pixels, the first temperature measurement values being indicative of the temperature of the surface, and correct the first temperature measurement values based on the pixel-associated temperature drift components.

12. The method as claimed in claim 1, further comprising: determining a temperature distribution on the surface based on the corrected first temperature measurement values, and wherein the infrared measurement system is configured as a handheld thermal imaging camera.

13. The method as claimed in claim 1, wherein the temperature drift components are determined continuously.

14. The infrared measurement system as claimed in claim 11, wherein an arrangement of reference pixels on the infrared detector array surrounds an array of measurement pixels arranged of the infrared detector array.

15. The infrared measurement system as claimed in claim 11, wherein the reference pixels are arranged in an array of measurement pixels arranged on the infrared detector array.

16. The infrared measurement system as claimed in claim 11, wherein the first thermal conductivity is less than the second thermal conductivity by a factor of 10.

17. The infrared measurement system as claimed in claim 11, wherein: the first thermal conductivity is configured by a first effective cross-sectional area and a first effective length of first connection elements, by way of which the measurement pixels are connected to the detector array substrate, the second thermal conductivity is configured by a second effective cross-sectional area and a second effective length of second connection elements, by way of which the reference pixels are connected to the detector array substrate, and one or more of the first effective cross-sectional area of the first connection elements differs from the second effective cross-sectional area of the second connection elements and the first effective length of the first connection elements differs from the second effective length of the second connection elements such that the first effective cross-sectional area divided by the first effective length does not equal the second effective cross-sectional area divided by the second effective length.

18. The infrared measurement system as claimed in claim 17, wherein on or more of (i) the second effective cross-sectional area of the second connecting elements is configured as a multiple of the first effective cross-sectional area of the first connecting elements and (ii) the first effective length of the first connection elements is configured as a multiple of the second effective length of the second connection elements.

19. The infrared measurement system as claimed in claim 18, wherein the first thermal conductivity is configured by first connection elements of at least 100 μm length and the second thermal conductivity is configured by second connection elements of at most 10 μm length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more detail in the subsequent description on the basis of exemplary embodiments that are illustrated in the drawings. The drawing, the description and the claims contain numerous features in combination. Expediently, a person skilled in the art will also consider the features individually and combine, these to form meaningful further combinations. The same reference signs in the figures denote the same elements.

(2) In the drawing:

(3) FIG. 1 shows an embodiment of an infrared measurement system according to the invention in a perspective front view,

(4) FIG. 2 shows an embodiment of an infrared measurement system according to the invention in a perspective rear view,

(5) FIG. 3 shows a perspective, schematic rear view of the infrared measurement system according to the invention in front of an object to be measured,

(6) FIG. 4 shows a schematic illustration of the components of the infrared measurement system according to the invention that are required to carry out the method according to the invention,

(7) FIG. 5a shows a greatly magnified, schematic top view of measurement pixels and reference pixels of a part of an infrared detector array according to the invention,

(8) FIG. 5b shows a schematic illustration of a section through a measurement pixel,

(9) FIG. 5c shows a magnified section of FIG. 5a,

(10) FIG. 5d shows an electrical equivalent circuit diagram of the infrared detector array corresponding to the plan view illustrated in FIG. 5a,

(11) FIG. 6a shows a schematic plan view of an embodiment of the infrared detector array according to the invention,

(12) FIG. 6b shows schematic illustrations of arrangements of measurement pixels and reference pixels on the infrared detector array,

(13) FIG. 7 shows an embodiment of the method according to the invention in a flowchart,

(14) FIG. 8a shows an “initial offset map”, which assigns initial measurement deviations T.sub.BP,offset and T.sub.MP,offset to reference pixels and measurement pixels, respectively, of the infrared detector array,

(15) FIG. 8b shows an “initial drift susceptibility map”, which assigns sensitivities of the initial measurement deviations a ∂T.sub.BP,offset and ∂T.sub.MP,offset to reference pixels and measurement pixels, respectively, of the infrared detector array,

(16) FIG. 9 shows a schematic illustration of the evaluation method steps according to the invention when using the initial measurement deviations T.sub.BP,offset and T.sub.MP,offset for determining the temperature drift components T.sub.drift,

(17) FIG. 10 shows a schematic illustration of the evaluation method steps according to the invention when using the initial drift susceptibilities ∂T.sub.BP,offset and ∂T.sub.MP,offset for determining the temperature drift components T.sub.drift,

(18) FIGS. 11a,b show a schematic illustration of the evaluation method steps according to the invention for homogenizing temperature measurement values T.sub.MP (a) before homogenization and (b) after homogenization of the temperature measurement values T.sub.MP.

DETAILED DESCRIPTION

(19) An infrared measurement system 10 according to the invention in the form of a handheld thermal imaging camera 10a is presented below. FIG. 1 and FIG. 2 show an exemplary embodiment of this thermal imaging camera 10a in a perspective front view and in a perspective rear view, respectively. The thermal imaging camera 10a comprises a housing 12 with a handle 14. The handle 14 allows the thermal imaging camera 10a to be held comfortably in one hand during its use. Furthermore, the housing 12 of the thermal imaging camera 10a has an output device in the form of a touch-sensitive display 18 and operating elements 20 for user input and control of the thermal imaging camera 10a on a side 16 facing a user during the use of the thermal imaging camera 10a. In particular, the thermal imaging camera 10a has a trigger 20a, by means of which a user can trigger a contactless establishment of a temperature of a surface 22 of an object 24 to be examined, in particular a temperature distribution on a surface 22 of an object 24.

(20) An entrance opening 28 in the housing 12 is provided on the side 26 of the housing 12 facing away from the user, thermal radiation emitted by the object 24, in particular emitted in a measurement, region 30 (see the dashed solid angle in FIG. 3) of a surface 22 of the object 24, being able to enter into the thermal imaging camera 10a through said entrance opening. A lens system 34 as an optical unit is situated directly behind the entrance opening 28 in a light tube 36 that reduces stray light. The lens system 34 is transmissive for radiation in the mid-wavelength infrared range and it serves to focus thermal radiation on an infrared detector array 36 (see, in particular, the explanations in relation to FIG. 5 and FIG. 6) of the thermal imaging camera 10a.

(21) Further, a camera 38 operating in the visual spectrum, by means of which a visual image of the measurement region 30 is recorded, is provided on the side 26 of the housing 12 facing away from a user during the use of the thermal imaging camera 10a in one exemplary embodiment of the thermal imaging camera 10a. This visual image can be output together with a thermal image 40 that was generated by a temperature measurement initiated by the user, in particular output in a manner at least partly superposed or overlaid on the thermal image 40. By way of example, the camera 38 can be realized as a CCD image sensor.

(22) On the lower side of the thermal imaging camera 10a, the handle 14 has a receptacle 42 for receiving an energy store 44 which, for example, may be embodied in the form of a rechargeable accumulator or in the form of batteries.

(23) The thermal imaging camera 10a serves to record a thermal image 40 of an object 24 to be examined, as illustrated schematically in FIG. 3. After activation of the thermal imaging camera 10a, the thermal imaging camera 10a contactlessly detects thermal radiation emitted from the surface 22 of the object 24 in the measurement region 30. The temperature established by the thermal imaging camera 10a characterizes the temperature of the surface 22 and should be understood to be a temperature distribution in this exemplary embodiment, said temperature distribution preferably being output in the form of a spatially resolved thermal image 40 to the user of the thermal imaging camera 10a. As a consequence of the trigger 20a being actuated by the user of the thermal imaging camera 10a, a thermal image 40 that is corrected by a temperature drift component T.sub.drift 46 is produced, output on the display 10 and stored in this exemplary embodiment.

(24) FIG. 4 schematically illustrates the components of the thermal imaging camera 10a according to the invention that are required to carry out the method according to the invention (see FIG. 7, in particular). These components are housed within the housing 12 of the thermal imaging camera 10a as electrical components and wired to one another. The components essentially comprise the infrared detector array 36, a control apparatus 48, an evaluation apparatus 50, a data communications interface 52, an energy supply apparatus 54 and a data memory 56.

(25) In particular, the control apparatus 48 represents an apparatus which comprises at least one control electronics unit and means for communication with the other components of the thermal imaging camera 10a, in particular means for open-loop and closed-loop control of the thermal imaging camera 10a. The control apparatus 48 is provided to control the thermal imaging camera 10a and to facilitate the operation thereof. To this end, the control apparatus 48 is signal-connected to the other components of the measurement appliance, in particular the infrared detector array 36, the evaluation apparatus 50, the data communications interface 52, the energy supply apparatus 54, the data memory 56, and also the operating elements 20, 20a and the touch-sensitive display 18. In an alternative exemplary embodiment of the thermal imaging camera 10a, the control apparatus 48 is also connected to a closure mechanism 58 (illustrated using dashed lines here).

(26) In FIG. 4, the energy supply apparatus 54 is preferably realized by the energy store 44 illustrated in FIG. 1 and FIG. 2.

(27) The evaluation apparatus 50 serves to receive and evaluate measurement signals of the infrared detector array 36 and has a plurality of functional blocks 60a-60g, which serve to process information, in particular to evaluate the received measurement signals. The evaluation apparatus 50 further comprises a processor, a memory and an operating program with evaluation and calculation routines (each not illustrated in any more detail). The evaluation apparatus 50 is provided to receive and evaluate (functional block 60a) measurement signals provided by the infrared detector array 36, in particular measurement signals provided by measurement pixels 62 and reference pixels 64 of the infrared detector array 36, which pixels are signal-connectable to the evaluation apparatus 50. In this way, temperature measurement values T.sub.MP (reference sign 66; see FIGS. 9 and 10, in particular) of a plurality of measurement pixels 62 and temperature measurement values T.sub.BP (reference sign 68; see FIGS. 9 and 10, in particular) of a multiplicity of reference pixels 64 are determined.

(28) Further, the evaluation apparatus 50 is provided to correct temperature measurement values T.sub.MP 66 by pixel-associated temperature drift component T.sub.drift (reference sign 46; see FIGS. 9 and 10, in particular) in each case. This correction is carried out by functional block 60f. The pixel-associated temperature drift component T.sub.drift 46 is evaluated by functional blocks 60b to 60e. The method steps that are satisfied or worked through by functional blocks 60a-60f are described in detail in conjunction with FIGS. 7, 9 and 10.

(29) In the already mentioned alternative exemplary embodiment in which the thermal imaging camera 10a has a closure mechanism 58 (illustrated using dashed lines in FIG. 4), the evaluation apparatus 50 further has a functional block 60g (illustrated using dashed lines), which serves to homogenize or reduce the variance of the temperature measurement values T.sub.MP 66, which have already been corrected by the temperature drift component T.sub.drift 46 according to the method according to the invention. The functionality of this functional block 60g is described in detail in the explanation relating to FIG. 11.

(30) Overall, the thermal imaging camera 10a, in particular the evaluation apparatus 50 thereof, is provided to carry out an evaluation of a thermal image 40 of the measurement region 30 on the basis of measurement signals from at least a plurality of measurement pixels 62 and reference pixels 64, with the thermal image 40 being corrected in respect of a pixel-associated temperature drift component T.sub.drift 46.

(31) The temperature measurement values T.sub.MP 66 and T.sub.BP 68 evaluated by the evaluation apparatus 50, the pixel-associated temperature drift components T.sub.drift 46, the temperature measurement values T.sub.MP.sup.corr corrected by the pixel-associated temperature drift components T.sub.drift 46 and thermal images composed from these data, in particular the thermal image 40 to be output, are provided to the control apparatus 48 by the evaluation apparatus 50 for further processing. In this way, there can be an output to a user of the thermal imaging camera 10a using the display 18 of the output apparatus. As an alternative or in addition thereto, the output can be implemented to an external data appliance (not illustrated in any more detail), such as, e.g., a smartphone, a computer or the like, using the data communications interface 52. Here, in the illustrated exemplary embodiment, the data communications interface 52 is embodied as a WLAN and/or Bluetooth interface. Moreover, an output to the data memory 56 for storing the established data and thermal images is conceivable.

(32) The infrared detector array 36 of the thermal imaging camera 10a captures thermal radiation from the infrared radiation spectrum, which, emanating from the surface 22 of the object 24 to be examined in the measurement region 30, enters the entrance opening 28 of the thermal imaging camera 10a (see FIG. 3). The thermal radiation entering into the entrance opening 28 is focused onto the infrared detector array 36 by means of the lens system 34, with illumination of at least a plurality of measurement pixels 62 (not illustrated in any more detail here).

(33) FIG. 5a shows a very much magnified, schematic plan view of part of an embodiment of the infrared detector array 36 having measurement pixels 62 and reference pixels 64. The plan view corresponds to the reproduction of an image of the surface 70 of the infrared detector array 36 obtained by means of scanning electron microscopy. The infrared detector array 36 consists of a semiconductor detector array substrate 72, which is made of silicon in this exemplary embodiment. Here, white surfaces represent the surface 70 of the infrared detector array 36, while the black regions reproduce depressions, in particular etched trenches 74 (see also FIG. 5b, in particular), into the detector array substrate 72. The infrared detector array 36 has a multiplicity of measurement pixels 62 and a plurality of reference pixels 64.

(34) The measurement pixels 62 and the reference pixels 64 are each arranged on the surface 70 of the infrared detector array 36, which simultaneously forms the surface 70 of the detector array substrate 72. As illustrated in the schematic section through a measurement pixel 62 in FIG. 5b (nota bene: black does not represent depressions here like in FIG. 5a), the measurement pixels 62—and, analogously, the reference pixels 64 not illustrated in more detail in section here either—each have a recess 76 and a capture structure 78, formed from monocrystalline silicon, for capturing infrared radiation. The recess 76 forms a cavity behind the capture structure 78, i.e., the recess 76 isolates the capture structure 78 from the detector array substrate 72, and so the capture structure 78 is arranged at a distance from the detector array substrate 72. The measurement pixels 62 and the reference pixels 64 further have connection elements 80, 82, by means of which they are connected to the detector array substrate 72 and kept away from the latter (FIG. 5c). Consequently, the measurement pixels 62 and the reference pixels 64 are each arranged as isolated, in particular undercut, capture structures 78 on the surface 70 of the infrared detector array 36 facing the object 24 to be examined. Each measurement pixel 62 and each reference pixel 64 forms a p-n diode that is sensitive, in principle, to infrared light.

(35) The measurement pixels 62 and the reference pixels 64 differ in terms of the connection to the detector array substrate 72. While the measurement pixels 62 are connected to the detector array substrate 72 using a few first connection elements 80, the reference pixels are connected to the detector array substrate 72 using many second connection elements 82. As shown in the magnified section of a part of FIG. 5a in FIG. 5c, the connection of the measurement pixels 62 in this exemplary embodiment is implemented by two first connection elements 80 with a length of 100 μm. By contrast, the reference pixels 64 are connected by twenty-four second connection elements 82 with a length of 10 μm. It should be noted that the two longer connection elements do not contribute significantly to the thermal conductivity since the latter is substantially determined by the substantially shorter connection elements 82.

(36) The second effective cross-sectional area A.sub.BP of all second connection elements 82—i.e., the sum of the individual cross-sectional areas (reference sign 126) of the second connection elements 82—is thus realized to be ten times the first effective cross-sectional area A.sub.MP of all first connection elements 80—i.e., the sum of the cross-sectional areas (reference sign 124) of the first connection elements 80—(the same depth of the connection elements 80 and 82 is assumed).

(37) Further, the first effective length L.sub.MP (reference sign 128) of each of the first connection elements 80 is realized to be ten times the second effective length L.sub.BP (reference sign 130) of each of the second connection elements 82. What this realizes is that each measurement pixel 62 is connected to the detector array substrate 72 with a first thermal conductivity λ.sub.MP 120, while each reference pixel 64 is connected to the detector array substrate 72 with a second thermal conductivity λ.sub.BP 122. The thermal conductivities of the corresponding connections are in each case denoted by arrows (reference signs 120 and 122) in FIG. 5d. In particular, what this realizes is that A.sub.MP/L.sub.MP is very much smaller than A.sub.BP/L.sub.BP. Consequently, according to the proportionality (see explanations in relation to formula (1))
λ=λ.sub.spec..Math.A/L,
the first thermal conductivity λ.sub.MP 120 is smaller by at least a factor of 100 than the second thermal conductivity λ.sub.BP 122 in the illustrated exemplary embodiment.

(38) On account of its mechanical connection via the connection elements 80 to the detector array substrate 72, each measurement pixel 62 is able to dissipate heat introduced by means of infrared radiation. The heat is dissipated to the detector array substrate 72 in the process. As a consequence of radiating-in infrared radiation P.sub.MP, a respective measurement pixel 62 heats by ΔT.sub.MP, wherein an electric resistance of the measurement pixel 62 in relation to a current I.sub.MP flowing through the measurement pixels 62 changes on account of the heating. The first thermal conductivity λ.sub.MP 120, with which the measurement pixels 62 are connected to the detector array substrate 72, is selected here in such a way that the measurement pixels 62 have a high sensitivity to radiated-in infrared radiation. On the basis of a detected infrared radiation, preferably depending on a detected intensity of radiated-in infrared radiation, each measurement pixel 62 produces an electrical measurement signal I.sub.MP, which correlates with the radiated-in thermal output of the infrared radiation P.sub.MP on the measurement pixel 62. In this exemplary embodiment, the current I.sub.MP represents the measurement signal of each measurement pixel, wherein the measurement signals of all measurement pixels 62 are provided independently of one another to the control apparatus 48. Alternatively, a voltage U.sub.MP could also be used as measurement signal. Each measurement signal provided by a measurement pixel 62 can be transmitted to the evaluation apparatus 50 of the infrared measurement system 10a for the purposes of establishing the respective temperature measurement value T.sub.MP 66, the latter being evaluated individually by said evaluation apparatus or in combination with other measurement signals of other measurement pixels 62.

(39) Since the reference pixels 61 are connected to the detector array substrate 72 with the second thermal conductivity λ.sub.BP 122, which is one hundred times greater in this exemplary embodiment than the first thermal conductivity λ.sub.MP 120, the reference pixels 64—in comparison with the measurement pixels 62—are substantially insensitive to infrared radiation incident from the measurement region 30. Consequently, the reference pixels 64 can be considered to be “blind pixels”. A heat flux dissipated from a respective reference pixel 64 to the detector array substrate 72 is therefore significantly larger than a heat flux dissipated from a measurement pixel 62 to the detector array substrate 72 on account of the thermal connection of the reference pixel 64. In a manner analogous to the measurement pixel 62, the reference pixel current I.sub.BP (alternatively the voltage U.sub.BP) of each reference pixel 64 can be provided to the control apparatus 48 as a measurement signal and, for the purposes of establishing a temperature measurement value T.sub.BP 68, can be transmitted from said control apparatus to the evaluation apparatus 50 of the infrared measurement system 10a, by means of which it is evaluated—in a manner analogous to the measurement signals of the measurement pixels 62.

(40) FIG. 5d reproduces an electrical equivalent circuit diagram for the infrared detector array 36 illustrated in FIG. 5a, in which resistors 84, 86, 87 of different dimensions—symbolized by different sizes of the resistors—represent the thermal conductivities λ.sub.MP and λ.sub.BP, by means of which the measurement pixels 62 and the reference pixels 64 are connected to the detector array substrate 72. Here, the small resistors 86 (five piece) symbolize the large thermal conductivity λ.sub.BP 122 of the reference pixels 64, (i.e., low thermal resistance), while the larger resistors 84 (four piece) symbolize the small thermal conductivity λ.sub.MP 120 (i.e., high thermal resistance) of the measurement pixels 62.

(41) FIG. 6a shows a schematic plan view of an embodiment of the infrared detector array 36 of the thermal imaging camera 10a according to the invention from the direction of view of the incident measurement radiation. In simplified fashion, each measurement pixel 62 and each reference pixel 64 is represented by a square. In an exemplary fashion, the plurality of measurement pixels 62 are arranged in a matrix-like fashion in the form of an array 88 on the surface 70 of the infrared detector array 36, in particular on the surface 70 of the detector array substrate 72. In this exemplary embodiment, the number of measurement pixels 62 is 41×31 in an exemplary fashion. Any other values are conceivable.

(42) In principle, the arrangement of the reference pixels 64 on the detector array substrate 72 is arbitrary but may be advantageously distributed for realizing a temperature drift component T.sub.drift 46 that is uniformly determinable over the entire infrared detector array 36. FIG. 6b illustrates different patterns which represent exemplary arrangements of measurement pixels 62 and reference pixels 64 on the infrared detector array 36. As also shown in FIG. 6a, the array 88 of measurement pixels 62 can be surrounded, for example, in particular framed, by an arrangement 90 of reference pixels 64; see FIG. 6b, top left. In a further exemplary embodiment, the reference pixels 64 can be arranged in regular fashion in the array 88 of measurement pixels 62 (see FIG. 6b, pattern top right, bottom left, bottom right), preferably be arranged in symmetric fashion, particularly preferably arranged in symmetric fashion in relation to at least one main axis of symmetry 92 of the infrared detector array (see FIG. 6b, pattern bottom right).

(43) The method according to the invention is described below on the basis of FIGS. 7 to 11.

(44) FIG. 7 illustrates a flowchart which reproduces an embodiment of the method according to the invention for contactlessly establishing the temperature of the surface 22, in particular for contactlessly establishing a thermal image 40 of the surface 22. The method is provided to be operated by a thermal imaging camera 10a, as was presented in conjunction with FIGS. 1 to 6.

(45) Proceeding from the measurement scenario illustrated in FIG. 3, a user of the thermal imaging camera 10a is interested in examining the temperature distribution on the surface 22 of an object 24. For the purposes of measuring the surface 22, the user directs the thermal imaging camera 10a onto the object 24 to be examined. In the meantime, the thermal imaging camera 10a continuously captures infrared radiation from the measurement region 30 by means of the infrared detector array 36 and, in the meantime, continuously displays a non-corrected thermal image on the display 18. In a first method step 200, the user actuates the trigger 20a of the thermal imaging camera 10a and thereby initiates the determination of the temperature drift components T.sub.drift 46 and the correction of the established temperature measurement values T.sub.MP 66 of the measurement pixels 62. In an alternative exemplary embodiment of the method, this initiation can be implemented in automated fashion, in particular repeated after a time interval or in virtually continuous fashion (see dashed arrow 224 in FIG. 7).

(46) Subsequently, the control apparatus 48 transmits the measurement signals, provided by the infrared detector array 36 at the time of initiation, to the evaluation apparatus 50. In method step 202, the evaluation apparatus 50 determines the temperature measurement values T.sub.BP 68 of a plurality of reference pixels 64 from their measurement signals. At the same time (or else in succession in one alternative), the evaluation apparatus 50 determines the temperature measurement values T.sub.MP 66 of a plurality of measurement pixels 62 from their measurement signals in method step 204. In this exemplary embodiment, these temperature measurement values T.sub.MP are temperature measurement values to be corrected according to the method according to the invention. The temperature measurement values are determined from the measurement signals in functional block 60a of the evaluation apparatus 50; see FIG. 4. Here, the functional block 60a converts the respective measurement signals I.sub.MP and I.sub.BP into temperature measurement values T.sub.MP 66 and T.sub.BP 68.

(47) Subsequently, the evaluation apparatus 50 loads an “initial offset map” 94, as illustrated in FIG. 8a, from the data memory 56. By means of the initial offset map 94, the evaluation apparatus 50 assigns unique initial measurement deviations T.sub.BP,offset 98 to the temperature measurement values T.sub.BP 68 of the plurality of reference pixels 64 (hatched in FIG. 8a) in method step 206. In FIG. 8a, the unique identification of the pixels is ensured in each case, for example, by way of the line and column number thereof. Here, the evaluation apparatus 50 forms value pairs (T.sub.BP, T.sub.BP,offset) for each reference pixel 64 to be evaluated by reading initial measurement deviations T.sub.BP,offset 98, assigned to the respective reference pixels 64, from the initial offset map 94. These value pairs can be presented vividly by plotting the established temperature measurement values T.sub.BP 68 on the ordinate axis against the initial measurement deviations T.sub.BP,offset 98 on the abscissa axis; see FIG. 9a. Method step 206 is carried out in functional block 60b of the evaluation apparatus 50; see FIG. 4.

(48) Subsequently, the evaluation apparatus 50 calculates the temperature drift behavior m.sub.BP 102 of the reference pixels 64 in method step 208 from the temperature measurement values T.sub.BP 68 of the reference pixels 64 as a gradient of a straight line 104, which models the plotted value pairs particularly well; see FIG. 9c. By way of example, this straight line can be obtained by means of a least squares fit or the like in one embodiment of the method. In particular, the following general equation applies to this straight line 104:
T.sub.BP=m.sub.BP.Math.(T.sub.BP,offset.sup.0−T.sub.BP,offset),
where T.sub.BP,offset.sup.0 is the abscissa intercept and m.sub.BP 102 is the temperature drift behavior of the reference pixels 64 as a constant of proportionality. The temperature drift behavior m.sub.BP 102 of the reference pixels 64 is determined in functional block 60c of the evaluation apparatus 50; see FIG. 4.

(49) In the method step 210, the evaluation apparatus 50 establishes a mathematical relationship between the temperature drift behavior m.sub.MP 100 of measurement pixels 62 and the temperature drift behavior m.sub.BP 102 of the reference pixels 64 for the purposes of determining the temperature drift components T.sub.drift 46. In the exemplary embodiment of the method illustrated in FIG. 9, the temperature drift behavior m.sub.MP 100 of the measurement pixels 62 is set to be equal to the temperature drift behavior m.sub.BP 102 of the reference pixels 64, i.e., m.sub.MP:=m.sub.BP. Method step 210 is carried out in functional block 60d of the evaluation apparatus 50; see FIG. 4.

(50) In method step 212, evaluation apparatus 50 determines the pixel-dependent temperature drift components T.sub.drift 46 from the temperature drift behavior m.sub.MP 100 of the measurement pixels 62. To this end, the evaluation apparatus 50 initially determines the associated initial measurement deviations T.sub.MP,offset 96 for each measurement pixel 62 to be evaluated—in this exemplary embodiment, these are those measurement pixels for which the temperature measurement values T.sub.MP were determined in method step 204—from the initial offset map 94 loaded in conjunction with method step 206 (see FIG. 8a; measurement pixels are illustrated in white therein). The temperature measurement values T.sub.MP 66 (ordinate) of a plurality of measurement pixels 62, which are plotted against the initial measurement deviations T.sub.MP,offset 96 (abscissa), are illustrated as a point cloud 106 in FIG. 9b. Thereupon, it is possible to calculate a temperature drift component T.sub.drift 46 belonging to a measurement pixel 62 as a product of the temperature drift behavior m.sub.MP 100 and the initial measurement deviation T.sub.MP,offset 96 belonging to the corresponding measurement pixel 62 according to the formula
T.sub.drift=m.sub.MP.Math.(T.sub.MP,offset.sup.0−T.sub.MP,offset).
This is illustrated in FIG. 9d as the dashed, calculated straight line 108, along which the values for the temperature drift component T.sub.drift 46, which are dependent on the initial measurement deviation T.sub.MP,offset 96 (abscissa axis), lie. The pixel-dependent temperature drift behavior T.sub.drift 46 according to method step 212 is determined in functional block 60e of the evaluation apparatus 50; see FIG. 4.

(51) Consequently, the evaluation apparatus 50 determines the temperature drift components T.sub.drift 46 from the temperature measurement values T.sub.BP 68 of the reference pixels 64 in method steps 206 to 212, using the functional blocks 60a to 60e of the evaluation apparatus 50.

(52) In method step 214, there is the final correction of the temperature measurement values T.sub.MP 66 of the measurement pixels 62 by the temperature drift component T.sub.drift 46 determined for the respective measurement pixel 62 by subtracting the two values. According to the illustration in FIGS. 9d and 9e, the straight line 108 is subtracted from the values of the point cloud, and so this correction can be elucidated by rotating the point cloud representing the temperature measurement values T.sub.MP 66 of the measurement pixels 64 (left-hand arrow in FIG. 9d). Method step 214 is carried out in functional block 60f of the evaluation apparatus 50; see FIG. 4.

(53) In an alternative or additional embodiment of the method, the “sensitivity of the initial measurement deviations ∂T.sub.MP,offset in relation to the influences of aging” 110 of the measurement pixels 62 and the “sensitivity of the initial measurement deviations ∂T.sub.BP,offset in relation to the influences of aging” 112 of the reference pixels 64 also can be used in place of the initial measurement deviations T.sub.MP,offset 96 and the initial measurement deviation T.sub.BP,offset 98. In a manner equivalent to the representations in FIG. 9 and in FIG. 7, the evaluation is then carried out in such a way that, for the purposes of determining the temperature drift components T.sub.drift 46, the temperature drift behavior m.sub.BP 102 of the reference pixels 64 is determined as a constant of proportionality between sensitivities of the initial measurement deviations ∂T.sub.BP,offset 112 of the reference pixels 64 and temperature measurement values T.sub.BP 68 (see the equivalence of FIG. 9 and FIG. 10 apart from the abscissa axis labels). Further, in a manner equivalent to FIG. 9d, the temperature drift components T.sub.drift 46 are determined from the temperature drift behavior m.sub.MP 100 by virtue of the temperature drift components T.sub.drift 46 of the respective measurement pixels 62 being calculated in the form of a function as a product of temperature drift behavior m.sub.MP 00 and sensitivities of the initial measurement deviations ∂T.sub.MP,offset 110 of the respective measurement pixels 62 (see the equivalence of FIG. 9d and FIG. 10d apart from the abscissa axis labels). In particular, this exemplary embodiment of the method according to the invention resorts to an “initial drift susceptibility map” 114 that is kept available in the data memory 56 (see FIG. 8b) In the manner equivalent to the method already described above, the evaluation apparatus 50 then assigns unique sensitivities of the initial measurement deviations ∂T.sub.BP,offset 112 to the temperature measurement values T.sub.BP 68 of the plurality of reference pixels 64 (illustrated in hatched fashion in FIG. 8b) using the initial drift susceptibility map 114 in a method step that is equivalent to method step 206.

(54) In the already mentioned alternative exemplary embodiment, in which the thermal imaging camera 10a has a closure mechanism 58 (illustrated using dashed lines in FIG. 4), the temperature measurement values T.sub.MP 66 can be homogenized. In the exemplary embodiment of the method according to the invention, shown in FIG. 7, this homogenization can be carried out following the correction of the temperature measurement values T.sub.MP 66 of the measurement pixels 62 by the temperature drift component T.sub.drift 46, i.e., after method step 214. As an alternative or in addition thereto, the homogenization can also be implemented at any other time, for example prior to calculating the temperature drift component T.sub.drift 46, i.e., before method step 206.

(55) Now, in method step 216, the incidence of infrared radiation on the infrared detector array 36 is initially suppressed by means of the closure mechanism 58 and the temperature measurement values T.sub.MP.sup.blind 66a are read. In FIG. 11a, five temperature measurement values T.sub.MP.sup.blind 66a are plotted in a diagram in exemplary fashion. Subsequently, a mean value <T.sub.MP.sup.blind> 116 is calculated in method step 218 from these temperature measurement values T.sub.MP.sup.blind 66a, said mean value coming very close to the temperature of the closure mechanism 58. Here, the actual temperature of the closure mechanism 58 is irrelevant. In FIG. 11a, the mean value <T.sub.MP.sup.blind> 116 is illustrated as a dashed line. Now, calculating a pixel-dependent deviation ΔT.sub.MP.sup.blind 118 from the mean value <T.sub.MP.sup.blind> 116 (small arrows in FIG. 11a) for the read measurement pixels 62 renders it possible to correct each measurement pixel 62 by precisely this deviation ΔT.sub.MP.sup.blind 118 in method step 220 by virtue of the correction values ΔT.sub.MP.sup.blind 118 being applied to the temperature measurement values T.sub.MP 66 and the temperature measurement values T.sub.MP 66 consequently being homogenized or fitted to the mean value <T.sub.MP.sup.blind> 116. The latter is illustrated in FIG. 11b, in which the temperature measurement values T.sub.MP.sup.blind 66a lie on the dashed line illustrating the mean value <T.sub.MP.sup.blind> 116 after the homogenization was carried out.

(56) Method steps 216 to 220 are carried out in functional block 60g of the evaluation apparatus 50; see FIG. 4.

(57) Subsequently, in method step 222, the corrected and possibly homogenized thermal image 40 is output to the user of the thermal imaging camera 10a using the display 18.