Method for Determining a Temperature without Contact and Infrared Measuring System

Abstract

A method for contactlessly establishing a temperature of a surface includes determining the temperature measurement values of the plurality of measurement pixels. The method further includes correcting the temperature measurement values by using in each case a pixel-associated temperature drift component. The method further includes at least temporarily suppressing an incidence of infrared radiation onto the infrared detector array using the closure mechanism of the infrared measurement system while temperature measurement values are being determined. The method further includes determining the temperature drift components using the temperature measurement values.

Claims

1. A method for contactlessly establishing a temperature of a surface using an infrared measurement system, the infrared measurement system including (i) an infrared detector array with a plurality of measurement pixels, each of the plurality of measurement pixels providing a measurement signal for establishing a temperature measurement value dependent on an intensity of the incident infrared radiation and (ii) a closure mechanism for suppressing an incidence of infrared radiation onto the infrared detector array, the method comprising: determining the temperature measurement values of the plurality of measurement pixels; correcting the temperature measurement values by using in each case a pixel-associated temperature drift component; at least temporarily suppressing an incidence of infrared radiation onto the infrared detector array using the closure mechanism of the infrared measurement system while temperature measurement values are being determined; and determining the temperature drift components using the temperature measurement values.

2. The method as claimed in claim 1, further comprising: determining a temperature drift behavior of the plurality of measurement pixels from the temperature measurement values in order to determine the temperature drift components.

3. The method as claimed in claim 2, further comprising: determining the temperature drift behavior of the plurality of measurement pixels as a constant of proportionality between initial measurement deviations of the plurality of measurement pixels and the temperature measurement values in order to determine the temperature drift components.

4. The method as claimed in claim 3, further comprising: determining the temperature drift behavior of the plurality of measurement pixels as a constant of proportionality between sensitivities of the initial measurement deviations in relation to the influences of aging of the plurality of measurement pixels and the temperature measurement values in order to determine the temperature drift components.

5. The method as claimed in claim 2, further comprising: determining the temperature drift components from the temperature drift behavior of plurality of measurement pixels.

6. The method as claimed in claim 5, further comprising: determining the temperature drift components from the temperature drift behavior of the plurality of measurement pixels using the temperature drift components of respective measurement pixels being calculated in form of a first function as a first product of temperature drift behavior and initial measurement deviations of the respective measurement pixels.

7. The method as claimed in claim 6, further comprising: determining the temperature drift components from the temperature drift behavior of the plurality of measurement pixels by using the temperature drift components of the respective plurality of measurement pixels being calculated in the form of a second function as a second product of the temperature drift behavior and the sensitivities of the initial measurement deviations in relation to influences of aging of the respective measurement pixels.

8. The method as claimed in claim 1, further comprising: determining the temperature drift components repeatedly at time intervals, in particular regularly, preferably continuously or virtually continuously.

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

10. An infrared measurement system for contactlessly establishing a temperature distribution on a surface, comprising: an infrared detector array with a plurality of measurement pixels, each of the plurality of measurement pixels configured to provide a measurement signal for establishing a temperature measurement value dependent on an intensity of the incident infrared radiation; a closure mechanism configured to suppress an incidence of infrared radiation onto the infrared detection array; and an evaluation apparatus configured to: determine the temperature measurement values of the plurality of measurement pixels; correct the temperature measurement values by using in each case a pixel-associated temperature drift component; at least temporarily suppress an incidence of infrared radiation onto the infrared detector array using the closure mechanism of the infrared measurement system while temperature measurement values are being determined; and determine the temperature drift components using the temperature measurement values.

11. The method as claimed in claim 1, wherein the method is configured for contactlessly establishing a temperature distribution on a surface.

12. The infrared measurement system as claimed in claim 10, wherein the infrared measurement system is a handheld thermal imaging camera.

Description

DRAWINGS

[0075] 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.

[0076] In the drawing:

[0077] FIG. 1 shows an embodiment of an infrared measurement system according to the invention in a perspective front view,

[0078] FIG. 2 shows an embodiment of an infrared measurement system according to the invention in a perspective rear view,

[0079] 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,

[0080] 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,

[0081] FIG. 5 shows a schematic top view of an embodiment of the infrared detector array according to the invention,

[0082] FIG. 6 shows an embodiment of the method according to the invention in a flowchart,

[0083] FIG. 7a shows an initial offset map, which assigns initial measurement deviations T.sub.MP,offset to measurement pixels of the infrared detector array,

[0084] FIG. 7b shows an initial drift susceptibility map, which assigns sensitivities of the initial measurement deviations a T.sub.MP,offset to the measurement pixels of the infrared detector array,

[0085] FIG. 8 shows a schematic illustration of the evaluation method steps according to the invention when using the initial measurement deviations T.sub.MP,offset for determining the temperature drift components T.sub.drift,

[0086] FIG. 9 shows a schematic illustration of the evaluation method steps according to the invention when using the initial drift susceptibilities T.sub.MP,offset for determining the temperature drift components T.sub.drift, and

[0087] FIGS. 10a,b show a schematic illustration of the evaluation method steps according to the invention for homogenizing the temperature measurement values T.sub.MP (a) before homogenization and (b) after homogenization of the temperature measurement values T.sub.MP.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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 18 and stored in this exemplary embodiment.

[0093] 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. 6, 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, a data memory 56 and a closure mechanism 58.

[0094] The infrared detector array 36 of the thermal imaging camera 10a comprises at least a plurality of measurement pixels 62 which are provided to capture 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).

[0095] Each measurement pixel 62 is provided to provide an electrical measurement signal U.sub.MP, for example a potential, at its output, said electrical measurement signal correlating with the radiated-in thermal output of the infrared radiation P.sub.MP on the measurement pixel 62. These pixel-dependent measurement signals U.sub.MP are initially output to the control apparatus 48 of the infrared measurement system, either individually or in combination with other measurement signals of other measurement pixels 62, and transmitted from said control apparatus to the evaluation apparatus 50 of the infrared measurement system 10.

[0096] In particular, the control apparatus 48 of the infrared measurement system 10 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 (via a circuit), the evaluation apparatus 50, the data communications interface 52, the energy supply apparatus 54, the data memory 56, the closure mechanism 58, and also the operating elements 20, 20a and the touch-sensitive display 18.

[0097] In FIG. 4, the energy supply apparatus 54 is preferably realized by the energy store 44 illustrated in FIG. 1 and FIG. 2.

[0098] The evaluation apparatus 50 serves to receive and evaluate measurement signals of the infrared detector array 36, i.e., the measurement signal U.sub.MP of the measurement pixels 62. The evaluation apparatus 50 has a plurality of functional blocks 60a-60f, which serve to process information, in particular to evaluate the received measurement signals. The evaluation apparatus 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 U.sub.MP provided by measurement pixels 62. In this way, temperature measurement values T.sub.MP (reference sign 64; see FIGS. 8 and 9, in particular) of a plurality of measurement pixels 62 are determined. Temperature measurement values established while the closure mechanism 58 suppresses an incidence of infrared radiation onto the infrared detector array are labeled by T.sub.MP.sup.blind (reference sign 66; see FIGS. 8 and 9) but should be treated analogously to temperature measurement values T.sub.MP from an evaluation point of view.

[0099] The evaluated temperature measurement values, in particular T.sub.MP 64 and/or T.sub.MP.sup.blind 66 can be provided for further processing to the control apparatus 48 by the evaluation apparatus 50.

[0100] Further, the evaluation apparatus 50 is provided to correct temperature measurement values T.sub.MP 64 by a pixel-associated temperature drift component T.sub.drift (reference sign 46; see FIGS. 8 and 9, in particular) in each case. This correction is carried out by functional block 60e. The pixel-associated temperature drift component T.sub.drift 46 is evaluated by functional blocks 60b to 60d. The method steps that are satisfied or worked through by functional blocks 60a-60e are described in detail in conjunction with FIGS. 6, 8 and 9.

[0101] In an alternative or additional exemplary embodiment of the infrared measurement system 10, the evaluation apparatus 50 further has a functional block 60f (illustrated using dashed lines), which serves to homogenize or reduce the variance of the temperature measurement values T.sub.MP 64, 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 60f is described in detail in the explanation relating to FIG. 10.

[0102] 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, in particular on the basis of temperature measurement values T.sub.MP.sup.blind, with the thermal image 40 being corrected in respect of a pixel-associated temperature drift component T.sub.drift 46.

[0103] The temperature measurement values T.sub.MP 64 and temperature measurement values T.sub.MP.sup.blind 66 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.

[0104] FIG. 5 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 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 this exemplary embodiment, the number of measurement pixels 62 is 4232 in an exemplary fashion. Any other values are conceivable. The method according to the invention is described below on the basis of FIGS. 6 to 9.

[0105] FIG. 6 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 5.

[0106] 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 64 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 228 in FIG. 7).

[0107] Subsequently, the control apparatus 48 transmits the measurement signals U.sub.MP, 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.MP 64 of a plurality of measurement pixels 62 from their measurement signals U.sub.MP. 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 T.sub.MP 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 U.sub.MP into temperature measurement values T.sub.MP 64. These temperature measurement values T.sub.MP 64 serve to produce a thermal image 40 of the object 24 to be examined. The goal of the further method is to subject these temperature measurement values T.sub.MP 64 to a correction in respect of the temperature drift component T.sub.drift 46.

[0108] To this end, in method step 204, an incidence of infrared radiation onto the infrared detector array 36 is at least intermittently suppressed by means of the closure mechanism 58 of the infrared measurement system 10 while the temperature measurement values T.sub.MP.sup.blind 66 are determined in method step 206 in a manner analogous to method step 202. These temperature measurement values T.sub.MP.sup.blind 66 that are independent of the incident infrared radiation form the basis according to the invention of the correction by the temperature drift component T.sub.drift 46.

[0109] Subsequently, the evaluation apparatus 50 loads the initial offset map 72, as illustrated in FIG. 7a, from the data memory 56. By means of the initial offset map 72, the evaluation apparatus 50 assigns unique initial measurement deviations T.sub.MP,offset 74 to the temperature measurement values T.sub.MP.sup.blind 66 of a plurality of measurement pixels 62 (in principle any plurality of measurement pixels) in method step 208. In FIG. 7a (and also 7b), 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.MP.sup.blind, T.sub.MP,offset) for each measurement pixel 62 to be evaluated by reading initial measurement deviations T.sub.MP,offset 74, assigned to the respective measurement pixels 62, from the initial offset map 72. Method step 208 is carried out in functional block 60b of the evaluation apparatus 50; see FIG. 4.

[0110] The value pairs (T.sub.MP.sup.blind, T.sub.MP,offset) can be presented by plotting the established temperature measurement values T.sub.MP.sup.blind 66 on the ordinate axis against the initial measurement deviations T.sub.MP,offset 74 on the abscissa axis. Subsequently, the evaluation apparatus 50 calculates the temperature drift behavior m.sub.MP 76 of the measurement pixels 62 in method step 210 from the temperature measurement values T.sub.MP.sup.blind 66 of the measurement pixels 62 as a gradient (constant of proportionality) of a straight line 78, which models the plotted value pairs particularly well; see FIG. 8c. In particular, the following general equation applies to this straight line 78:

T.sub.MP.sup.blind=m.sub.MP.Math.(T.sub.MP,offset.sup.0T.sub.MP,offset),

where T.sub.MP,offset.sup.0 is the abscissa intercept and m.sub.MP 76 is the temperature drift behavior of the measurement pixels 62 as a constant of proportionality. The temperature drift behavior m.sub.MP 76 of the measurement pixels 62 is determined in functional block 60c of the evaluation apparatus 50; see FIG. 4.

[0111] In method step 212, the evaluation apparatus 50 determines the pixel-dependent temperature drift components T.sub.drift 46 for the already established temperature measurement values T.sub.MP 64 (not T.sub.MP.sup.blind 66), which should be corrected by the temperature drift components T.sub.drift 46i.e., for which the temperature measurement values T.sub.MP were determined in method step 202. For the purposes of determining the temperature drift components T.sub.drift 46, the method according to the invention uses the temperature drift behavior m.sub.MP 76 of the measurement pixels 62 determined from the temperature measurement values T.sub.MP.sup.blind 66.

[0112] The evaluation apparatus 50 now initially determines the associated initial measurement deviations T.sub.MP,offset 74 for each measurement pixel 62 to be evaluated, for which there is present a temperature measurement value T.sub.MP 64 to be corrected, from the initial offset map 72 loaded in conjunction with method step 208 (see FIG. 7a). 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 74 (abscissa), are illustrated as a point cloud 80 in FIG. 8b. 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 76 and the initial measurement deviation T.sub.MP,offset 74 belonging to the corresponding measurement pixel 62 according to the formula

T.sub.drift=m.sub.MP.Math.(T.sub.MP,offset.sup.0T.sub.MP,offset)

[0113] This is illustrated in FIG. 8d as the dashed, calculated straight line 82, 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 (abscissa axis), lie. The pixel-dependent temperature drift behavior T.sub.drift 46 according to method step 212 is determined in functional block 60d of the evaluation apparatus 50; see FIG. 4.

[0114] Consequently, the evaluation apparatus 50 determines the temperature drift components T.sub.drift 46 from the temperature measurement values T.sub.MP.sup.blind 66 of the measurement pixels 64 in method steps 206 to 212, using the functional blocks 60a to 60d of the evaluation apparatus 50.

[0115] In method step 214, there is the final actual 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. 8d and 8e, the straight line 82 is subtracted from the values of the point cloud 80, and so this correction can be elucidated by rotating the point cloud 80 representing the temperature measurement values T.sub.MP 64 of the measurement pixels 62 (left-hand arrow in FIG. 8d). Method step 214 is carried out in functional block 60e of the evaluation apparatus 50; see FIG. 4.

[0116] 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 84 of the measurement pixels 62 also can be used in place of the initial measurement deviations T.sub.MP,offset 74. In a manner equivalent to the representations in FIG. 8 and in FIG. 6, 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.MP.sup.blind 76 of the measurement pixels 62 is determined as a constant of proportionality (gradient) between sensitivities of the initial measurement deviations T.sub.MP,offset 84 of the measurement pixels 62 and temperature measurement values T.sub.MP.sup.blind 66 (see the equivalence of FIG. 8 and FIG. 9 apart from the abscissa axis label). Further, in a manner equivalent to FIG. 8d, the temperature drift components T.sub.drift 46 are determined from the temperature drift behavior m.sub.MP 76 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 and sensitivities of the initial measurement deviations T.sub.MP,offset 110 of the respective measurement pixels 62 (see the equivalence of FIG. 8 and FIG. 9 apart from the abscissa axis label). In particular, this exemplary embodiment of the method according to the invention resorts to an initial drift susceptibility map 86 that is kept available in the data memory 56 (see FIG. 7b). 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.MP,offset 84 to the temperature measurement values 66 of a plurality of measurement pixels 62 using the initial drift susceptibility map 86 (FIG. 7b) in a method step that is equivalent to method step 208.

[0117] In an alternative or additional exemplary embodiment, the temperature measurement values T.sub.MP 64 can be homogenized. In the exemplary embodiment of the method according to the invention, shown in FIG. 6, this homogenization can be carried out following the correction of the temperature measurement values T.sub.MP 64 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 204.

[0118] 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 66 are read. In FIG. 10a, five temperature measurement values T.sub.MP.sup.blind 66 are plotted in a diagram in exemplary fashion. Subsequently, a mean value <T.sub.MP.sup.blind> 88 is calculated in method step 218 from these temperature measurement values T.sub.MP.sup.blind 66, 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. 10a, the mean value <T.sub.MP.sup.blind> 88 is illustrated as a dashed line. Now, calculating a pixel-dependent deviation T.sub.MP.sup.blind 90 from the mean value <T.sub.MP.sup.blind> 88 (small arrows in FIG. 10a) for the read measurement pixels 62 renders it possible to correct each measurement pixel 62 by precisely this deviation T.sub.MP.sup.blind 90 in method step 2220 and thus to homogenize the temperature measurement values T.sub.MP.sup.blind 66 or to adjust the mean value <T.sub.MP.sup.blind> 88. The latter is illustrated in FIG. 10b, in which the temperature measurement values T.sub.MP.sup.blind 66 lie on the dashed line illustrating the mean value <T.sub.MP.sup.blind> 88 after the homogenization was carried out. The deviation T.sub.MP.sup.blind 90 determined using the temperature measurement values T.sub.MP.sup.blind 66 is transferable to the yet to be determined, or already determined, temperature measurement values T.sub.MP 64, and so, according to the invention, there can likewise be homogenization of the temperature measurement values T.sub.MP 64 established in the case of an open closure mechanism 58.

[0119] Method steps 216 to 220 are carried out in functional block 60f of the evaluation apparatus 50; see FIG. 4.

[0120] 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.