Abstract:
A device ( 100 ) for the contactless non-destructive testing of a surface ( 106 ) by measuring its infrared radiation includes an electromagnetic radiation source ( 1 ) emitting excitation radiation which is directed onto the surface ( 106 ) to be tested ( 26 ), a detector ( 9 ) arranged in a direction towards said surface ( 106 ) and a first IR filter medium ( 2 ) provided between the radiation source ( 1 ) and the surface ( 106 ). In response to radiation impinging onto the surface ( 106 ), detection radiation is emitted by the surface ( 106 ) and fed to the detector ( 9 ). At least a second filter medium ( 3 ) is provided between the first filter medium ( 2 ) and the surface ( 106 ) to be tested ( 26 ), wherein a space ( 24 ) is provided between the first and the second filter medium ( 2, 3 ) creating a coolant channel and being connected to a coolant drive for actively exchanging the fluid for the cooling fluid circulation ( 4 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European Patent Application No. 16 001 320.7 filed Jun. 10, 2016, the disclosure of which is hereby incorporated in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a device for the contactless and non-destructive testing of a surface by measuring its infrared radiation. 
       Description of Related Art 
       [0003]    The contactless testing of surfaces based on the generation and measurement of transient periodic heating and cooling processes uses an excitation source for heating the surface to be tested as well as an infrared detector which measures the infrared radiation from the heated surface. This method is called photothermy if electromagnetic radiation in the ultraviolet, optical or infrared range is used for excitation. 
         [0004]    Such a device is described in US 2013/0037720 using one or more incoherent electromagnetic radiation sources, a detector providing and arrange on an detection axis and comprising a measuring area a testing area defining an area to be measured of the test surface and an imaging device arranged on the detection axis for mapping the testing area onto the measuring area of the detector. The radiation sources are adapted to generate a pulse like or intensity modulated excitation radiation, e.g. flash lights directed onto the surface to be tested in the testing area. The device according to US 2013/0037720 uses e.g. flash lamps allowing to provide a measurement to evaluate the exact thickness of a surface coating having a value between several micrometers and up to 0.1 millimeter. 
       SUMMARY OF THE INVENTION 
       [0005]    The prior art device is adapted to evaluate at least one of the group of physical properties from thickness, thermal diffusivity, thermal effusivity, thermal conductivity, heat capacity, density, adhesion, porosity, composition, degree of hardening or phase of one or more thin coatings applied to a substrate. The substrate can be a sheet of metal and the coatings have a thickness of e.g. 10 to 100 micrometer. The prior art device is not capable to determine such properties, if the underlying substrate is a thick body as a cement brick. It is also not capable to evaluate such properties, if the thickness of the coating is 1 millimeter to 10 millimeter. Such a device cannot be used to provide a thickness indication for test specimen having a body with a thickness of several centimeters. 
         [0006]    It is a further object of the present invention to provide the measuring device as a handheld mobile device since the coatings to be tested are often in e.g. building structures and cannot be transferred into a laboratory environment. 
         [0007]    The object of the invention is achieved with a device for the contactless and non-destructive testing of a surface by measuring its infrared radiation thereof, comprising: one or more electromagnetic radiation sources adapted to emit excitation radiation which can be directed onto the surface to be tested; a detector arranged on a detection axis directed towards the surface to be tested; and a first IR filter medium provided between each radiation source and the surface to be tested, wherein, in response to radiation impinging onto the surface to be tested, detection radiation is emitted by the surface to be tested and fed to the detector, wherein at least a second filter medium is provided between the first filter medium and the surface to be tested, wherein a space is provided between the first and the second filter medium creating a coolant channel for a cooling fluid circulation and wherein the coolant channel is connected to a coolant drive for actively exchanging the fluid for the cooling fluid circulation. 
         [0008]    Preferably, two insulation walls are provided between each electromagnetic radiation source and the detector, wherein a space is provided between the first and the second insulation wall creating a coolant channel for a cooling fluid circulation. 
         [0009]    The coolant channel for the filter media and the coolant channel of the insulation walls are directly connected; then a continuous cooling channel can be provided where a cooling gas is blown through the channel. It is a further advantage, if the coolant flow is initially directed between the filter media, or glass sheets for the transmittal of the excitation radiation, and then to direct the preheated fluid between the insulation walls. 
         [0010]    The device preferably comprises housing walls having free ends adapted to be applied against the surface to be tested, creating a free space between the surface to be tested and the second filter medium creating a further coolant channel for a cooling fluid circulation. 
         [0011]    The fluid can be an inert gas, especially nitrogen. Then the coolant drive can be a blower. The fluid can also be a liquid, if the coolant channels are hermetically sealed. The coolant drive would then be a pump. 
         [0012]    An imaging device can be arranged on the detection axis for mapping the surface to be tested onto the detector. 
         [0013]    The excitation radiation from the radiation sources can be fed to the surface to be tested at an inclination to the detection axis avoiding direct reflection of remaining IR excitation portions. An imaging device can be arranged between the radiation source and the surface to be tested. 
         [0014]    A control unit is used to determine, based on the measured IR response from the detector, at least one of the group of physical properties from thickness, thermal diffusivity, thermal effusivity, thermal conductivity, heat capacity, density, adhesion, porosity, composition, degree of hardening or phase of one or more coatings applied to a substrate. 
         [0015]    The electromagnetic radiation sources may be incoherent electromagnetic radiation sources. 
         [0016]    Further embodiments of the invention are laid down in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings, 
           [0018]      FIG. 1  shows a schematic cross section view of a device according to a first embodiment of the invention applied against a surface to be tested; 
           [0019]      FIG. 2  shows a schematic cross section view of a device according to a second embodiment of the invention applied against a surface to be tested; 
           [0020]      FIG. 3  shows a schematic cross section view of a device according to a third embodiment of the invention applied against a surface to be tested; 
           [0021]      FIG. 4  shows a very schematic cross section view of a device according to a fourth embodiment of the invention; 
           [0022]      FIG. 5  shows a very schematic cross section view of a device according to a further embodiment of the invention; 
           [0023]      FIG. 6  shows a very schematic cross section view of a device according to a further embodiment of the invention; and 
           [0024]      FIG. 7  shows a diagram of temperature against time. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows a schematic cross-section view according to an embodiment of the invention wherein the device is a handheld device  100  applied against a surface to be tested being part of the test specimen  6 . It is noted that the device  100  has side walls  101  with a free end surface  102  to be positioned against the surface  106  of the material to be tested. The body of the testing device  100  with said side walls  101  has back walls  111  forming a handheld device, which can have attachments, handles, power lines or it can be a battery operated testing device  100 . 
         [0026]    Reference numeral  1  relates to radiation sources especially capable to provide radiation outside the IR-range. The cross-section view of  FIG. 1  can relate to two sources  1  directing their excitation radiation  5  according to the main optical axis  25  of the radiation source towards the testing surface  26  on test specimen  6  from which radiated heat radiation  8  is emitted and targets an infrared detector  9  provided somewhere in between the radiation sources  1  as shown in  FIG. 1 . A collimating element can be provided along the optical axis  35  of the detector  9 . It is of course possible that the radiation sources  1  are arranged in a circle around the testing surface  26  with a central detector. In any case, it is preferred that at least one insulation wall  18  and/or  28  is provided between the radiation source  1  and the detector  9 . 
         [0027]    The radiation leaving the radiation source  1  in the beam  5  passes through at least two filter media  2  and  3  separated by a free space  24 . Between the filter surface  3 , which is nearer to the surface layer  16  to be tested, and said surface layer  16  is a further free space  34 . 
         [0028]    In the embodiment shown in  FIG. 1 , the free space  24  in front of the radiation source  1 , i.e. between the radiation source  1  and the surface to be tested  106  provides a channel for a coolant medium which flows according to arrow  4  through the side wall  101  and leaves the device at the back wall  111 . Therefore, it flows between the insulation walls  18  and  28  in parallel to the side walls  101  and vertically to the surface  106  to be tested. This coolant flow, which is provided for both radiation sources, avoids a significant rise in temperature and heating of the filter media  2  and  3  (to a predetermined extent) as well as of the insulation walls  18  and  28 . Thus, it will be mainly the radiation from the radiation sources  1  which heats up the body base element  7  at its surface  106  as well as it avoids a direct heating of the detector  9  through infrared radiation coming from said intermediate walls  18  and  28  and/or from said optical wall elements. It is of course possible to invert the flow direction  4  to the opposite direction of the arrows  4 , especially in view of the fact that a greater heat impact will probably be provided by the filter media  2  and  3  in comparison to the IR radiation coming from the insulation walls  18  and  28 . Filter media  2  and  3  can be made of glass or acryl glass. 
         [0029]    In the embodiment of  FIG. 1 , it may also be provided an optional inlet and outlet in relation to the free space  34  but this is not shown in the drawing. Additionally, the side walls  101  have an inlet  112  and an outlet  113  for each radiation source  1  to allow a further coolant flow through the radiation source cavity  115 . 
         [0030]    The coolant medium is preferably just air or a gas and specifically an inert gas as nitrogen. Using a fluid medium for the coolant channel  24  is in principle possible since the radiation has just to pass the filter medium  2  and  3  which is in principle possible without any contact with the lamp arrangements. 
         [0031]    The radiation sources  1  are acting for longer times between 0, 1 and 1000 seconds depending on the materials and thickness in order to deposit a high amount of energy in the testing area  26  to heat the surface layer  16  having a thickness of up to several millimeters. Exposition times between 1 and 100 seconds are preferred. This high input of energy as well as the longer use of the radiation sources  1  creates secondary infrared centers which have to be avoided through taking away the heated up materials through the coolant flow. The coolant channels  24  are not only provided in the drawing plane but preferably encompass the radiation sources  1  on all side where radiation can be emitted and be directed into the direction of the sensor  9 . 
         [0032]    The coolant flow according to the coolant flow direction  4  and between inlet  112  and outlet  113  can be closed into a coolant cycle or coolant circuit with a coolant drive (not shown), effectively exchanging the coolant or cooling fluid being in the spaces  24  and  115 . 
         [0033]    The coolant or cooling fluid can be a gas and then the coolant drive can be a blower. The coolant or cooling fluid can be a liquid and then the coolant drive can be a pump. 
         [0034]      FIG. 2  shows a schematic cross-section view according to a second embodiment of the invention wherein the device is also a handheld device  100 . Same reference numerals throughout the drawings are related to identical features in different embodiments. 
         [0035]    The test specimen  6  has a surface layer  16  of a thickness which is to be determined. An usual thickness for this testing device is between Device  100  with side walls  101  and back walls  111  is applied onto the surface layer  16  creating the free space  34  shielded from the excitation source  1  through optical windows and filter media  2  and  3  and thus behind the coolant channel  24 . Here the radiation sources  1  are provided inside source cavity  115  having an opening  14  for the inlet and outlet of coolant medium according to circular flow  114 . In difference to the embodiment of  FIG. 1  the free space  34  has through side openings  124  connections to the environment where a test specimen near coolant flow  134  takes away any heat from the inside surface of filter medium  3  and central filter medium  13 . Central filter medium  13  can be a lens collimating radiation from the testing surface  26  and is a pass filter for IR radiation. Nevertheless lens  13  provides a clear physical separation between the free space  34  on the side near the surface layer  16  to be tested and the sensor  9  so that no medium flow is possible between the free space  34  and the area around sensor  9 . 
         [0036]    The coolant flow according to the coolant flow direction  4  and outlet flow  134  can be enhanced through blowers (not shown), effectively exchanging the fluid being circulated in the spaces  24 ,  34  and  115 , thus reducing the impact of heated walls  18  and  28  as well as optical filter media  2  and  3 . 
         [0037]      FIG. 3  shows a schematic cross-section view according to a third embodiment of the invention wherein the device is also a handheld device  100 . The main difference between the embodiments of  FIG. 1  and  FIG. 2  and the embodiment of  FIG. 3  is the absence of dedicated coolant channels. Space  24  is only connected to the back room, the same is true for the front space  34 , which is only connected via the central radiation channel with the environment. Filter medium  3  nearer to the testing surface  26  is far thicker than the filter medium  2  on the other side of the free space  24 . This thicker filter medium  3  provides the advantage of better insulation of the remaining direct heating radiation onto the testing area. 
         [0038]      FIG. 4  shows a very schematic cross section view of a device according to a fourth embodiment of the invention. The device  100  according to  FIG. 4  can have distance enabling elements to apply the device against a surface  106  to be tested. Therefore side walls  101  with a free end surface  102  to be positioned against the surface  106  of the material to be tested are not shown. 
         [0039]    Reference numeral  1  relates to one radiation source capable to provide radiation outside the IR-range. The cross-section view of  FIG. 4  can also relate to more sources  1  outside the drawing plane and directing their excitation radiation  5  towards the testing surface  26  of test specimen  6  from which radiated heat radiation  8  is emitted and targets an infrared detector  9  provided somewhere in between the radiation sources  1  as shown in  FIG. 1 . The surface to be tested comprise a layer or coating  16  and a base element  7 . The base element  7 , e.g. a ciment brick, having a thickness of several centimeters is covered by a surface layer  16  of one to several millimetres and it is one aim of the invention to correctly evaluate the thickness of layer  16 . Possible materials to be tested are rubber, plastics, ceramic materials, wood, metal, leather, paint, glass and ciment. The filter media  2  and  3  are provided in an oblique manner with their main optical axis  25  directed towards the testing area  26 . In any case, it is preferred that at least one insulation wall  18  and/or  28  is provided between the radiation source  1  and the detector  9  with a coolant flow  4  in between. The walls  18  and  28  are shielding the detector  9  from a direct IR exposure from the radiation source(s)  1 . The two filter media  2  and  3  with its intermediate coolant flow  4  are shielding the detector  9  from a reflected or diffracted IR exposure from the radiation source(s)  1 . 
         [0040]    A reflector element (not shown) can be provided behind and around the excitation source  1  in the cavity  115 . 
         [0041]    One or the other filter medium  2  or  3  can also be a lens to focus the excitation beam  5  on the testing area  26  including a spectral filtering. It is also possible to provide a third filter medium in front of said two filter media  2  and  3  creating a further second parallel free space  24  to shield the testing surface  26  even more efficiently from a direct IR heating. 
         [0042]      FIG. 5  shows a very schematic cross section view of a device according to a further embodiment of the invention. The device  100  according to  FIG. 5  comprises a reflective/transmissive element  40 . It is transmissive for the excitation radiation emitted from the radiation source  1  and it is reflective for IR radiation emitted from the surface  26  of specimen  6  to be tested. The reflective/transmissive element  40  is positioned in a predetermined angle to reflect the heat radiation  8  onto the detector provided on the side. 
         [0043]    Here, elements  101  and  121  of a housing are shown. There will be further elements encompassing the lamp and radiation source  1  with the IR filter medium  2  and the side wall  101  as well as the detector cavity back wall  121  which will be readily added by persons skilled in the art. Detector  9  closes the right side with side wall  101  and back wall  121  creating the separated further space  34  as already shown in  FIG. 1 . 
         [0044]      FIG. 6  shows a very schematic cross section view of a device according to a further embodiment of the invention. The device  100  according to  FIG. 6  comprises a reflective collimating mirror  45 . Radiation source  1  and detector  9  are mounted with parallel main optical axes  25  and  35 . Then the excitation beam  5  directed towards the reflective collimating mirror  45  is diverted towards the testing area  26 . Therefore any IR portion of the excitation radiation  1  will be mainly reflected in a very different direction than the IR radiation detected by detector  9  along its optical axis  35 . 
         [0045]    As explained with  FIGS. 5 and 6 , the differentiating features of one of the embodiments from  FIGS. 1 to 4  can be combined with further features from any other embodiment. 
         [0046]    So it is possible to add shielding walls  18  and  28  to the embodiments of  FIG. 5 or 6  and imaging elements like the central filter medium  13  can be added as well. 
         [0047]      FIG. 7  shows a diagram of temperature against time. A control unit is integrated in device  100  or attached to device  100  to handle the sensor output of detector  9 . It provides the curve  70  of the temperature in Kelvin as result of the received radiation and the time passed receiving the radiation which may have already stopped for a coating of a specific thickness on a substrate. A further coating having a different thickness on the same substrate provides the curve  71 . Then the control unit is adapted to calculate a thickness value for the coating. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE SIGNS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 radiation source 
               
               
                   
                 2 
                 filter medium 
               
               
                   
                 3 
                 filter medium 
               
               
                   
                 4 
                 coolant flow direction 
               
               
                   
                 5 
                 excitation radiation 
               
               
                   
                 6 
                 test specimen 
               
               
                   
                 7 
                 base element 
               
               
                   
                 8 
                 heat radiation 
               
               
                   
                 13 
                 central filter medium 
               
               
                   
                 14 
                 opening 
               
               
                   
                 16 
                 surface layer 
               
               
                   
                 18 
                 insulation wall 
               
               
                   
                 24 
                 coolant channel 
               
               
                   
                 25 
                 main optical axis of radiation 
               
               
                   
                   
                 source 
               
               
                   
                 26 
                 testing surface 
               
               
                   
                 28 
                 insulation wall 
               
               
                   
                 34 
                 further free space 
               
               
                   
                 35 
                 optical axis of detector 
               
               
                   
                 40 
                 reflective/transmissive 
               
               
                   
                   
                 element 
               
               
                   
                 45 
                 collimating mirror 
               
               
                   
                 60 
                 temperature 
               
               
                   
                 65 
                 time 
               
               
                   
                 70 
                 detector curve of a coating 
               
               
                   
                 71 
                 detector curve of a different 
               
               
                   
                   
                 coating 
               
               
                   
                 100 
                 testing device according to a 
               
               
                   
                   
                 first embodiment 
               
               
                   
                 101 
                 side wall 
               
               
                   
                 102 
                 free end surface 
               
               
                   
                 106 
                 surface 
               
               
                   
                 111 
                 back wall 
               
               
                   
                 112 
                 inlet 
               
               
                   
                 113 
                 outlet 
               
               
                   
                 114 
                 circular flow 
               
               
                   
                 115 
                 source cavity 
               
               
                   
                 121 
                 detector cavity back wall 
               
               
                   
                 124 
                 side opening 
               
               
                   
                 134 
                 test specimen near coolant 
               
               
                   
                   
                 flow