DE1933854A1 - Infrared thermograph - Google Patents

Description

PATENT LAWYERS

DR. I. MAAS
DR. W. PFEIFFER
_{Ca <ip} -ΐρςη.β? Ο "-F-VOITHENLEITNER

UNQERER3TR.2B.TEI. 39 ob 36

Barnes Engineering Company Stamford, Connecticut / USA

Infrared thermograph

The invention relates to an infrared thermograph, with which the thermal image of a field of view on a photosensitive surface is imaged, and in particular an infrared thermograph, with which several various visual representations can be generated, one of which is a color representation.

An infrared camera according to the invention is a thermograph of the type described in U.S. Patent 2,895,049. Such infrared -Thermograph responds to infrared radiation and produces a

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thermal image of a scanned field of vision. The thermograph described in the US patent mentioned has an infrared detector with which a field of view is optically scanned. The detector generates electrical signals as a function of the infrared radiation strength of the objects in the scanned field of view of the thermograph. The signals from the infrared detector are amplified, processed and fed to a modulator in the form of a glow tube, with which a film _{1 is} exposed in a grid-like manner synchronously with the scanning of the field of view, producing a recorded thermal image called a thermogram. The intensity of the glow tube is modulated as a function of the signals generated by the infrared detector and a black-and-white image is obtained, the gray tone of which is a function of the infrared radiation intensity of the objects in the scanned field of view Thermograph is. Although this system has proven to be sufficient for a wide range of applications in medicine and industry, the use of the glow tube as a modulator - and in particular the intensity modulation of the brightness of such a tube, however, has some difficulties. Perhaps the most obvious disadvantage is the overriding of the Glow tube, which can lead to its destruction. Even more important, but less obvious, are the changes in the spectral intensity distributions that are obtained when the modulator glow tube is controlled at different loads. These changes in the spectral intensity distributions of the modulator glow tube make it difficult to provide a photosensitive surface or a photosensitive film which correctly reproduces the radiation intensity which is to be measured and recorded. the

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Difficulty is somewhat reduced if you have the selects the correct glow tubes and the correct film for the reproduction in black and white, but it becomes larger, when trying to generate thermal color images of the field of view.

In thermography it is often advantageous to use the thermal Image of the field of view of the thermograph in one Generate variety of grids. Z.3. it is sometimes difficult with a continuous spectrum or with an analogue display in black and white areas on the To distinguish thermographs that have almost the same temperature. To have such a representation in the system , which is described in the above-mentioned United States patent, electronic devices in Form of a large number of level-setters used, so that the drive current is applied in discrete steps to the modulator glow tube on the thermograph appear as levels of the same color. Further electronic devices were developed, which the isotherms by a current pulse each time the levels of the control current for the modulator Glinmröhre change is placed on the tube. These. Digital or step thermograms, as well as the isotherms that are generated in the process, require additional electronic devices and close the disadvantage of the deterioration of the glow tube with different drive currents. There is therefore a need to a much simpler and more versatile means of generating various forms of representations.

The invention therefore aims to provide an improved thermograph which produces different visual representations

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and the described disadvantages of known thermographs not has. Another object of the invention is an improved thermograph which has a large number of easily changeable Displays generated without the need for additional and complicated equipment.

In an embodiment of the invention is a light-sensitive surface with a light source of constant brightness synchronized with the scanning of an infrared detector Scanned via a field of view of a thermograph gropes. A filter with several different filter components modulates the beam of the constant light source, before it hits the light-sensitive surface. In one embodiment according to the invention, the filter depending on the signals that are generated by the infrared detector, controlled, creating a thermal Image of the field of view of the thermograph in a predetermined arrangement according to the filter components of the Filters is generated. In another embodiment According to the invention, the angular deflection of a small Mirror of a galvanometer controlled by the detector output to modulate the light source through the filter.

A wide variety of filter arrangements can be used which have continuous or analog black and white and color reproduction, gradual or digital color reproduction. or black and white reproduction, step or digital pattern with isotherms, a ^ hot background for each of the patterns mentioned, and a variety of different ones of the above includes the specified pattern. '

The invention is explained by way of example with the aid of the figures. .. ".-".

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Figure 1 shows schematically a thermograph according to the invention.

Figure 2 shows a black and white filter with variable density, which can be used in the thermograph of FIG.

Figure 3 shows a color filter with a continuous spectrum, which can be used in the thermograph of FIG.

Figure J »shows a digital or step filter for either Black and white or for color which can be used in the thermograph according to FIG. :

Figure 5 shows a digital or step filter with isotherms for the thermograph of Figure 1 and further illustrates the use of a "hot background".

Figure 6 shows a multiple choice filter device and control mechanism for the filter device, which is located in the thermograph can be used according to Figure 1.

Figure 7 shows a schematic view of another embodiment of a thermograph with a further light module · tion system according to the invention and. <

FIG. 8 shows a schematic view of the light modulation system according to FIG. Figure 7, which can also be used in the thermograph according to Figure X , from the side. ■!

In Figure 1 is an infrared thermograph with a scanning plan mirror 10 shown, which is of a drive mechanism 1; , is driven. The planar scanning mirror 10 scans the field of view of the thermograph in the * X and Y directions at

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and the radiation reflected from the mirror is from a Cassegrain optic with a primary element 11 and ~ s

a secondary element 12 and collected on an infrared ■■ "" Detector 14 focused. In the way of the optical System on the detector 14 collimated beam is arranged a chopper 25, which is driven by a motor 16 will. The chopper 25 has alternating sections that are opaque and transparent to the radiation incident on the detector. Therefore the detector measures 14 the difference in radiation emitted by the field of view it is imaged and the radiation from the opaque portion of the chopper plate. Electrical signals, which are generated by the infrared detector 14 as a function of the received radiation difference are amplified and evaluated synchronously in the circuit 1-8. the The construction described is similar to that described in of the aforementioned United States patent and presented by the applicant is established.

The device according to the invention differs from the known System of the type and construction required for the generation the thermogram or the visible representation of the thermal Image of the field of view of the thermograph is used. According to the invention, a light source 26 of the Current source of the circuit 18 excited so that this light source 26 burns with constant brightness / It is not a: special one Light source required, however, it is preferred that light source 26 be fully visible. ijichtSpectrum generated and an ordinary tungsten filament lamp is for this purpose suitable. An opening 28 is provided above the light source 26 which is a narrow beam of light from the light source £ 6 fades out. The narrow light beam from the source 26 becomes

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Imaged via converging lenses 23 on a light-sensitive surface or on a film 2Ί via a mirror 22. The mirror 22 is attached to the scanning mirror 10. If, therefore, the scanning mirror 10, the field of view of the thermal; graphs scans, the light beam from the light source 26 sweeps synchronously across the film 24. To generate a thermal image of the field of view of the thermograph, the light beam of the constantly bright light source 26 must be modulated according to the intensity of the radiation, which each Raster point of the field of view '■ ' is received. This is effected according to the invention with a filter 30 which is arranged in the light beam of the source 26 before it strikes the photosensitive surface or the film 2k. The filter 30 is located in the system above the opening 28 and is driven by a converter. 32, which in turn is controlled by the electronic evaluation circuit 18. The converter must be able to shift the filter 30 by small distances in dependence on the current from the utilization circuit 18. This current is of course related to the intensity of the radiation received by detector Ii. A commercially available combined spring motor amplifier from a conventional paper tape recorder has been found to be sufficient for this purpose. It is clear, however, that other types of transducers can be used, for example a (loudspeaker) voice coil, a piezoelectric transducer and others. As will be detailed below, the filter 30 consists of a large number of different filter components which are arranged in a very specific grid as required. By moving the filter 30 with the converter 32 transversely to the opening 28

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of the light source 26, the light beam is modulated by different amounts of light or different colors of the. ^; Spectrum as a function of the superimposed elements of the filter 30 are allowed to pass. This in turn results · a pattern on the film ¹ 24, which produces a thermal image of the visual field of the thermograph.

The advantage of the system according to the invention consists in the great flexibility of this system for generating visual representations of the field of view of the thermograph in a very simple manner. Examples of different filter arrangements are shown in FIGS. FIG. 2 shows a filter whose density changes continuously from white to black and is used to generate thermograms which are also obtained with a known system. The variable density filter transmits different amounts of light from the source 26 to the film, depending on the transparency of the particular effective portions of the filter. This arrangement also has an advantage over the known systems, since it avoids the intensity modulation of a glow tube and uses a light source of constant brightness, as a result of which more uniform images can be generated. An opaque section 38 is also located on the filter of Figure 2. The opaque section 38 is turned on for blanking during the retrace intervals after every _tf line and after every frame. The transducer 32 is excited by the drive mechanism 13 in such a way that it brings the impermeable section 38 of the filter 30 in front of the light source 2§ both in the horizontal and in the vertical direction during the return intervals. This is a very simple and expedient way of carrying out the return control, which in the known arrangement by reducing

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. the control current of the light source was effected, which The disadvantage is that the light source is exposed to great stress. The return control in the described Wise is preferred, but can be used as an alternative a rotor with an impermeable element driven by the scanning mechanism can also be used and, if desired, to cover the light source 26 is actuated during the return intervals.

Figure 3 shows a .Filter 30 with a continuous Color spectrum from red to purple. When using this The black and white film can be filtered through a usual filter Color film to be replaced. Thermograms are generated in color, in which the hot objects are in the field of view red and the cold objects appear purple on the film.

The continuous spectrum either in black and white or in color produces an analog representation of the thermal image of a field of view of the thermograph. Other types of visual representations may in a simple ^way: are obtained with the system according to the invention. In Figure 2 | For example, a step filter or digital filter is shown, which consists of discrete band filters or step filters. FIG. 4 shows 10 levels which are 10 different shades of gray from black to completely transparent in black and white and 10 different color filters in color. The: Thermogram, which is generated either in black and white or in color ·, shows 10 different temperatures of the visual field •. The advantage of the digital thermogram is there! that all areas on the thermogram that have the same temperature also have the same color: what the under-

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separating temperatures makes it easier. It is clear that fewer stages can be used than shown, if only larger temperature changes are to be observed. It is also clear that, if desired, the temperature values can easily be reversed by reversing the order of the filters. Hot objects become purple or black and cold objects shown in red or white in the field of view. With black-and-white representations, larger temperature differences can be used on the white side of the filter combined with smaller percentage changes on the black side so that a kind of logarithmic filter is created. This makes sense because the eye is more sensitive in black and less receptive to changes in white is. Enlarging the steps in the white part of the spectrum makes the thermograms easier to read.

FIG. 5 shows a further embodiment of the filter according to FIG. 4, in which the digital filter stages 40 are separated from one another by transparent or opaque areas 42 between the stages. The thermogram produced with it, regardless of whether it is black and white or color; and whether it is analog or digital, contains the equivalent white or black isothermal lines depending on whether transparent or opaque areas 42 are used. Areas itiit different temperatures are thereby delimited by white or _(black lines, it 4φβ easy being regions with different temperatures | Differentiate to ■ Further, when the temperature change, a filter element to d ^ m other is known 'to, the temperature differences. It is not necessary that the isotherms separate or delimit each element so that

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Any combination or predetermined arrangement for black or white isotherms can be provided. Figure 5 'also shows a permeable section M next to the impermeable return section 38. Again, either' as in the case of black and white or in the case of color thermograms, the normally cold background of the object to be thermographed can be photographed as pure white, by placing the clear filter element ¹ I ¹ I directly under the coldest (purple or black) part of the filter 30. Such a simulated hot background is highly desirable because very cold objects such as hair, gangrenous teeth, and cold extremities can be silhouetted against a white background in medical thermography. In the case of thermograms of many cold extremities, these are so mixed up with the background that they can hardly be identified in the thermogram. In the case of digital representations, the only necessary requirement is that each filter component of the filter is at least as wide as the light beam from the light source 26 which emerges from the opening 28. An opening 0.058 cm (0.02 inch) wide has been found to be sufficient, but other opening sizes can be used. The filter 30 should be arranged close to the opening, since the light beam diverges when it comes out of the opening. However, this distance has not been found to be critical and it depends on the size of the opening and the optical structure of the system.

The filter 30 can be of any convenient shape. The length and the height depend on the drive capacity of the modulation converter 32. One form of filter that has proven to be useful is that only the variable density or the color spectrum is printed directly on a film and the bare film is used as a filter.

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is turned. Such a filter works satisfactorily 'for scanning a line in 3M seconds, which is an image j with 90 lines in 1 1/2 minutes and a picture with 180 lines. the same field of view in about 3 minutes.

Figure 6 shows another possible application of the system ^ in which a large number of rapid grids can be selected. The spring motor 32 controls an arm 36 'on one disc JlJ is attached, the several different filter grids 50. contributes .. By only the entire arrangement with the spring motor or the filter in the * disc in the vertical direction are moved, the display can easily be changed optionally without the filter grid from the Disc must be removed and reinserted for it.

Another embodiment with a light source more constant Brightness according to the invention, which is suitable for generating a thermal image in several modes of representation, is shown in FIG. The type of thermograph of this embodiment is described in German patent application P 17 72 36 ^ .7 : ". i. of May 3, 1968 explained.

In the embodiment according to FIG. 7, the modulated The glow tube of the object according to the aforementioned German patent application is replaced by a light source of constant brightness and this light source .wird with a large number modulated by filter devices. The Ensatζ of the glow tube results in a more reproducible visual representation, who do not From the contingencies of a changeable light source with. their inherent spectral problems

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is-. A more flexible system is created in which different types of visual representation, including a Color representation, are possible without difficulty. Color representations, which are not possible with the system according to the cited German patent specification can be obtained. The digitized or tiered representations that were previously only obtained with extensive electronic devices can be achieved in a simple manner just by choosing the setting of a filter.

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FIG. 7 shows an infrared thermograph with an objective lens: 21, which images the field of view onto an infrared detector 66 via a flat scanning mirror 52. The plane mirror 52, which is driven by a drive device 54, is pivoted in the X and Y directions in such a way that it scans the field of view of the thermograph in two coordinates. The radiation incident on the mirror is reflected to the infrared detector. The driver 54 also operates a solenoid 56 to which a blackened slide 58 is attached. The solenoid 56 is energized after each horizontal line, thereby pushing the slide 58 in front of the detector 60 and creating a reference standard for the electronic control prior to the scanning of each line. Electrical signals are from. the infrared detector 60 in response to the difference in radiation received from the field of view. These signals are pre-amplified in the evaluation circuit 62 and evaluated synchronously. The construction of the thermograph, as far as it has just been described, is similar to that described in the aforementioned German patent application. The embodiment according to the invention differs from known thermographs in the type and construction that is used to generate the thermogram or to visually display the thermal image of the field of view of the thermograph. In the illustrated embodiment according to the invention, a modulation system 64 (Figures 8 and 8) is provided which has a light source 66 with a fixed luminosity or brightness. The 'light source is a condenser i> 8 and a mirror imaged about 72 to one! Mirror%. The mirror 76 is part of a galvanometer 74. The galvanometer, which is not shown in detail, is constructed in the usual way, ie it works with a coil that rotates in a magnetic field. With such a mechanism, the coil is suspended between the poles of a permanent magnet on a tinem

Torsion thread and the electrical connections to the spool

by the thread on which the bobbin is suspended and by a flexible helically wound thread, the attached to the bottom of the coil 1st. The rotation of the bobbin creates a restoring force in the thread that corresponds to the direction of rotation the coil is opposite «When the restoring torque and the torque produced by the current on the coil is conditional / are the same, the galvanometer adjusts itself to a very specific deflection. The mirror 76 represents • Provides an opportunity to read the galvanometer deflection.

For example, I found a Minneapolis-Honeywell galvanometer M 33OOT useful for this purpose, among other things; proven. A lens 78 in front of the fialvanometer mirror 76 images the condenser 68 onto a diaphragm 80. The light incident on the mirror is made parallel. A small opening or hole 82 in the aperture 80 defines the Auf-Beiohnung8-Abtas ^ P ^un pSe all light that passes through the opening 82 comes from a small area of the capacitor 68 defined by the image of the opening 82 generated on the condenser 68 by the galvanometer lens 78. Rotation of galvanometer 74 causes this point to scan a line across condenser 68. A filter 70 is placed next to the condenser 68 or between the elements of the condenser. Therefore, the color or intensity of the light which passes through the opening 82 depends on the position of the galvanometer mirror-76. The light exiting aperture 82 is reflected by a beam splitter 84 and thrown onto a concave mirror 85 located on the back of the scanning mirror 52. The concave mirror 85 images the opening 82 onto a light-sensitive surface 86, for example a film. The use of the beam splitter · 8 * has the effect that the light source is related to the dl · plane; 4 · γ photosensitive surface is centered, whereby

the coma is reduced. Because the concave mirror 85 arranged on the back of the planar scanning mirror 52 is scanning the field of view of the thermograph as well as painting over the photosensitive ones Surface 86 performed simultaneously and the synchronization difficulties avoided.

The type of visual representation depends on the type of Filters and the choice of the light-sensitive surface. For example, if the filter is a color filter that consists of six to eight filter sections that cover the include the visible spectral range from blue to red and the light-sensitive surface 86 is color-sensitive, a color representation can be obtained. Such a filter produces a quantization of the recording so that successive temperature inversions appear as different discrete areas of color on the image. the Color recording makes it easier to distinguish between different object temperatures because the eye can see differences in color can perceive much better than different shades of gray »-. A grayscale representation can, however, also be obtained by replacing the color filter with a black and white filter with gradation of gray. Greater flexibility is achieved by using a wide variety of filters. Each, de.ruin Figures 2 to 5 shown Filters can be used for this embodiment to generate various representations. A The advantage of this invention is that a fixed filter unit can be used. This eliminated those related to the weight and size of the filter are the problems encountered in a system that is slidable Filter devices used as shown in Figure 1

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is provided. Another advantage of this invention is the sensitivity of the galvanometer, which means that very little driving force is required. The galvanometer is a sensitive instrument that is suitable for perceiving and measuring small currents that occur during perception of infrared radiation are usually and not exceptionally present. The "light modulation system according to FIG. 7 can be used in the thermograph shown in FIG be used.

In the case of the embodiment according to FIGS. 7 and 8, the infrared detector 60 is imaged in the form of a grid onto a field of view of a thermograph by the plane mirror 52, the signals being applied to a galvanometer 7% of a modulation system 6H . The deflection of the galvanometer mirror 76 as a function of the signals received by the infrared detector modulates a light source 66 with a fixed intensity via a filter 70, which can be a color filter, for example. This is optically effected in that the light source 66 is focused on the galvanometer mirror 76 by a condenser and a galvanometer lens 78 is used which images the condenser onto an opening. The rotation or pivoting of the galvanometer has the effect that-the opening describes a line on the condenser, .-., In which the filter is located and therefore determines the color of the light that falls through the filter 70 .. By changing the filter many visual representations possible.

The invention provides an improved thermal imager in which a current-modulated glow discharge tube is replaced by a constant light source luminance and the ^von: said light source is emitted light modulated at a plurality of filters. By replacing the glow tube, a better visual representation can be achieved, which is not

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depends on the randomness of a variable light source and the associated spectral problems. The invention provides a more flexible system - with different types of visual representation, including color representation, which can be obtained without complicated measures. The parb representations, which were previously not possible, can be easily produced. Digitized or stepped representations, which were only possible with a great deal of electronic effort, can be obtained in a simple manner by choosing a specific filter.

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Claims (1)

$ 1 Claims Infrared thermograph for the visual representation of the infrared radiation received from a field of view with an infrared detector, which scans the field of view and generates signals corresponding to the infrared energy incident on it, with devices to synchronize with the scanning of the field of view with the light of a light source to paint light-sensitive surface, the light source being modulated by these signals to generate a thermal image of the field of view, characterized by a constantly bright light source (26), a filter (30) with a large number of different filter elements (38, ¹ JO, 42, ¹ J ¹ I), which are arranged in a very specific way and by means (18, 32) for modulating the light of this light source with this filter in accordance with the signals of "the infrared _t red detector (I ¹ J ), whereby a thermal image of the field of view of the thermograph is generated. 2. Infrared ^ thermograph according to claim 1, characterized in that the means for modulating the light of the light source (26) with the filter have a converter (32) which the filter in front of the light source as a function of the signals from the infrared -Detector (I ¹ J) go out, shifts. 009819/1279 IO 3. Infrared thermograph according to claim 1, characterized in that the means for modulating the Light source with the filter a swiveling mirror, . gel, a first optical device with a stationary one Filter device for focusing the light from this light source on the pivotable mirror, a Aperture, a second optical device for imaging the first optical device on this diaphragm, devices for controlling the pivotable mirror according to the signals sent by the infrared detector. tor, thereby modulating the light source and means for imaging and scanning them Opening on the light-sensitive surface. Synchronous with the scanning of the detector over a field of view having. - k. Infrared thermograph according to claim 1, 2 or 3, characterized in that the plurality of filter components of the filter have a filter with a continuous spectrum either from black to white or from red to purple. 5. Infrared thermograph according to claim 1, 2 or 3, characterized in that the filter has an opaque portion ( 38) at one end which is placed above the light source when the transducer is activated by the scanning means during the return intervals of the defrost cycle . β, infrared thermograph according to claim 1, 2 or 3, characterized in that the filter has a transparent section (M) next to a filter element,. that represents the coldest color of the multitude of different filter elements to create a hot background * on the light-sensitive surface. 00981971270 Ii 7. Infrared thermograph according to claim 1, 2 or 3 '' characterized in that the plurality of filter elements of the filter device are discrete filter elements (4Ö) with different colors, either black, white or in color, have * · ■; '"-" 8. Infrared thermograph according to claim 7 »daduiicli characterized in that at least two of the: discrete filter elements (40) with different colors are separated by transparent sections (42) ^: 9. Infrared thermograph according to claim 7 »daiäürch gekönn- f records that at least two of the discrete filter elements (kb) with different colors duich ge sections (42) from one another rs side