Abstract:
A portable noncontact thermometer comprising a housing defining an aperture for ingress of incident thermal energy in a field of view. A graphical display is fixed with respect to the housing. The thermometer further comprises a thermopile array including a plurality of thermopile elements positioned inside the housing so as to be impinged by the incident thermal energy. The thermometer further includes processing circuitry in electrical communication with the thermopile array. The processing circuitry is operative to produce on the graphical display a thermal image of the field of view. The processing circuitry is further operative to determine a temperature of a target location within the field of view based on electrical signals derived from a subset of the thermopile elements. The subset of thermopile elements may be a single thermopile element located approximately at a center of the thermopile array.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to portable IR thermometers. More particularly, the invention relates to a portable IR thermometer having thermal imaging capability. 
     Portable infrared (IR) thermometers allow a user to ascertain the temperature of a remote target using a point and click technique. These instruments are commonly utilized for purposes ranging from automotive diagnostics to food safety. Often, these devices will use a single thermopile element at which the thermal energy is focused to ascertain the temperature at the aim point. In order to determine the aim point, the thermometers may be equipped with a laser pointer that emits a laser beam in the forward direction. Various details regarding the construction and operation of noncontact thermometers may be discerned from U.S. Pat. Nos. 4,634,294, 5,640,015 and 6,234,669, each of which is incorporated herein by reference in its entirety for all purposes. 
     In contrast to a thermometer, thermal imaging cameras are used to create a high quality thermal image of a scene (such as an industrial machine being inspected for predictive maintenance). These cameras typically use a microbolometer array of at least 160×120 pixels to generate the thermal scene. As known in the art, both the microbolometer arrays and the cameras in which they are used are relatively expensive. Therefore, they may be undesirable for many applications in which a more economical noncontact thermometer would be sufficient. 
     SUMMARY OF THE INVENTION 
     According to one aspect, the present invention provides a portable noncontact thermometer comprising a housing defining an aperture for ingress of incident thermal energy in a field of view. A graphical display is fixed with respect to the housing. The thermometer further comprises a thermopile array including a plurality of thermopile elements positioned inside the housing so as to be impinged by the incident thermal energy. Various sizes of thermopile arrays may be utilized in accordance with the present invention, including a 4×4 array, a 10×10 array, a 16×16 array or a 32×32 array. 
     The thermometer further includes processing circuitry in electrical communication with the thermopile array. The processing circuitry is operative to produce on the graphical display a thermal image of the field of view. The processing circuitry is further operative to determine a temperature of a target location within the field of view based on electrical signals derived from a subset of the thermopile elements. 
     In some exemplary embodiments, the subset of thermopile elements is a single thermopile element located approximately at a center of the thermopile array. The single thermopile element may occupy greater surface area on the array than other thermopile elements. Preferably, the single thermopile element may be directly connected to an amplifier without multiplexing. 
     Embodiments are contemplated in which the subset of thermopile elements are connected to the processing circuitry without passing through a multiplexer in a common package with the thermopile array. Thermopile elements included in the subset may be connected to a respective amplifier, either inside or outside of the common package. In contrast, thermopile elements other than the subset are preferably connected to the processing circuitry by passing through a multiplexer in the common package. 
     Preferably, the processing circuitry will be further operative to show the temperature of the target location on the graphical display. For example, the temperature of the target location may be superimposed on the thermal image. In addition, the target location may be indicated by crosshairs superimposed on the thermal image. 
     In accordance with another aspect, the present invention provides a noncontact thermometer comprising a housing defining an aperture for ingress of incident thermal energy in a field of view. A graphical display is also provided. The thermometer further includes a thermopile detector including a thermopile array having a plurality of thermopile elements arranged in rows and columns. The thermopile detector further has at least one multiplexer in a common package with the array through which a subset of the thermopile elements are connected. 
     The thermometer further includes processing circuitry in electrical communication with the thermopile detector so as to receive electrical signals from the thermopile elements other than the subset through the at least one multiplexer and from the subset without multiplexing. The processing circuitry is operative to produce on the graphical display a thermal image of the field of view. The processing circuitry is further operative to determine a temperature of a target location within the field of view based on electrical signals from the subset of thermopile elements. For example, the subset of thermopile elements may be a single thermopile element. 
     Another aspect of the present invention provides a method of detecting temperature of a target location within a field of view. One step of the method involves providing a thermopile array having a plurality of thermopile elements. Electrical signals produced at a subset of the thermopile elements are amplified using a narrower bandwidth amplifier to yield amplified non-multiplexed signals. Electrical signals produced at thermopile elements other than the subset are multiplexed to yield multiplexed signals. The multiplexed signals are amplified using a wider bandwidth amplifier to yield amplified multiplexed signals. The amplified multiplexed signals and the amplified non-multiplexed signals are then processed to produce a thermal image of the field of yield. In addition, the amplified non-multiplexed signals are processed to determine temperature of the target location. 
     A still further aspect of the present invention provides a thermopile detector configured as a discrete electronic package. The detector comprises a thermopile array having a plurality of thermopile elements. At least one multiplexer is located in the package. A subset of the thermopile elements are connected to respective output terminals of the package without multiplexing. Thermopile elements other than the subset are connected to an output terminal of the package shared with at least one other thermopile element (other than the subset) via a multiplexer. 
     Additional aspects of the present invention, including various combinations and subcombinations of the disclosed elements, will be apparent from the remainder of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a portable IR thermometer constructed in accordance with the present invention; 
         FIG. 2  is a rear view of the thermometer of  FIG. 1  showing the display at which thermal images and temperature readings are shown; 
         FIG. 3  is a diagrammatic representation showing certain internal components of the thermometer of  FIG. 1 ; 
         FIGS. 4 and 5  illustrate exemplary displays which may be shown on the display device; 
         FIG. 6  is a diagrammatic representation of a thermopile array in which all of the thermopiles feed signal information to multiplexers; 
         FIG. 7  is a diagrammatic representation of a thermopile array similar to  FIG. 6  but with one of the thermopiles bypassing the multiplexers; and 
         FIG. 8  is a diagrammatic representation of a 32×32 thermopile array with a larger center pixel being utilized for temperature measurement. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
       FIGS. 1 and 2  illustrate an exemplary hand-held thermometer  10  constructed in accordance with certain principles of the present invention. As will be described more fully below, thermometer  10  includes an internal thermopile detector which collects radiated energy in the instrument&#39;s field of view. The energy, typically in the form of infrared (IR) radiation, is isolated and focused on the detector. The thermopile detector includes a thermopile array which functions to produce a thermal image of the scene in the field of view. Even though the resolution of the thermal image may be less than achievable with a more expensive microbolometer camera, it will be adequate for aiming purposes. The energy detected at a subset of the thermopile elements in the array is also used to determine a temperature value of a target location in the scene. Embodiments of the present invention provide accuracy comparable to prior art noncontact thermometers that lack imaging capability. 
     As shown, thermometer  10  includes a housing  12  in which various internal components (including the thermopile detector) are located. While any suitable material can be utilized, housing  12  is preferably formed of a rigid high impact plastic material. As shown, housing  12  includes a handle  14  on which a trigger  16  is located. Trigger  16  places the thermometer in a “scan” (or active measurement mode). A graphical display  18  is preferably located at the rear of thermometer  10 . In this case, a variety of information is shown on display  18 , including a reading of the target temperature. Various functions of thermometer  10  are controlled by buttons  20 ,  22  and  24 . 
     Certain internal components of thermometer  10  will be explained with reference to  FIG. 3 . Thermal energy from the field of view passes through an aperture  26  defined in housing  12 , where it is directed by optics (such as a collimating lens  28 ) to a thermopile detector  30 . Thermopile detector  30  includes a thermopile array having a number of thermopile elements arranged as pixels in rows and columns. Typical array sizes may include 4×4, 10×10, 16×16 or 32×32. A larger array will generally provide a higher resolution thermal image than a smaller array. Additional circuitry may be incorporated into a discrete electronic package along with the thermopile array to yield detector  30 . 
     As shown, the multiple outputs of detector  30  (the number of which will depend on the size of the array) are fed to respective amplifiers  32  and  34   a - c . The output of amplifier  32  is then fed to an input of analog-to-digital (A/D) converter  36 . The outputs of amplifiers  34   a - c  are fed to a multiplexer  38 , before passing to A/D converter  36 . 
     As will be explained more fully below, amplifier  32  is preferably a narrow bandwidth amplifier having a high signal-to-noise (SN) ratio. In this regard, amplifier  32  preferably receives output from a subset of thermopile elements (typically a single thermopile element) in the array. Amplifiers  34   a - c , in contrast, will generally be wider bandwidth amplifiers that each receive signals from multiple thermopile elements that have been multiplexed using multiplexers located on-board thermopile detector  30 . For example, each such multiplexer may be in electrical communication with all thermopile elements in a particular row or in a particular column (except for the subset fed through amplifier  32 ). 
     The digital signal resulting from A/D converter  36  is then fed to an internal microcontroller  40 . Microcontroller  34  utilizes preprogrammed algorithms to convert the digital detector data into thermal image and temperature information. A memory  42  is associated with microcontroller  40  to store temperature information, along with firmware and other information (such as emissivity) utilized during operation. An ambient temperature sensor  44  is provided so that the cold junction (or body) temperature will be known in calculating the target temperature. The ambient temperature sensor can be a separate component or it may be mechanically combined with the thermopile array (but is not a thermopile itself). For example, the ambient temperature sensor can be a thermistor. The function buttons  20 ,  22  and  24  are collectively indicated at  46 . 
     As shown, graphical display  18  is in electrical communication with microcontroller  40 . Preferably, for example, display  18  may be configured as a suitable LCD display capable of showing a thermal image. A color LCD display is especially preferred for this purpose. Some functions of the thermometer may be selected using a graphical user interface (GUI) run on microcontroller  40  (as indicated at  48 ). 
       FIGS. 4 and 5  illustrate exemplary screens which may appear on display  18  in accordance with the present invention. Referring first to  FIG. 4 , a thermal image is shown depicting the scene in the instrument&#39;s field of view. In this case, for example, a thermal image of an electric motor  50  being inspected is shown on the display. A “cross hairs”  52  is located in the center of the scene, superimposed on the image. As one skilled in the art will appreciate, the cross hairs represent the aim point at which the thermometer will take a temperature reading. In this case, for example, the display indicates a temperature of 234.5° F. at the intersection of cross hairs  52 . Like cross hairs  52 , this temperature reading may be superimposed on the thermal image. One skilled in the art will appreciate that the thermal image facilitates aiming of the instrument to ensure that the reading taken is of the correct location. 
       FIG. 5  illustrates an alternative screen where display of the thermal image has been suspended so that the user can operate the GUI. Three tabs  54 ,  56  and  58  are located at the bottom of the screen proximate to buttons  20 ,  22  and  24 , respectively. In this case, tab  54  contains the word “Save,” tab  56  contains the word “Menu” and tab  58  contains the word “Light.” These words indicate the function that may be performed by pressing the corresponding button. These functions may change depending on where a particular screen appears in the GUI menu tree. Thus, there is a direct association between each button and the on-screen information located above it. 
     Various icons may also be displayed on the screen. In this case, for example, the measured temperature (e.g., 234.5° F.) is preferably shown in large font in the center of the screen. The current emissivity, in this case 0.50, may also be displayed on the screen. In this example, the screen shows that both high and low alarms have been set. Specifically, thermometer  10  may be equipped with an audible indicator, such as a buzzer, that is activated when either a high or low condition is encountered. In other words, if the temperature either exceeds the high alarm level or drops below the low alarm level, a conspicuous indicator may be provided. The words “Hi” or “Lo” on the screen may blink to inform the user of the relevant alarm condition. 
       FIG. 6  illustrates a technique for producing a thermal image using a thermopile array that would generally be unsuitable for accurate spot temperature detection. In this example, a 3×3 thermopile array has a total of nine thermopile elements  60   a - i  arranged in three rows and three columns. Each row of thermopile elements feeds to a respective multiplexer  62   a - c  located in the same discrete electronic package with the thermopile array. The output of each multiplexer forms a respective pin of the electronic package for connection to external components. Thus, as shown, each of multiplexers  62   a - c  is connected to the input of a respective off-chip amplifier  64   a - c . The amplifier outputs are then multiplexed at  66  before being digitized for image processing. 
     Because amplifiers  64   a - c  receive a multiplexed output, they need to have a much higher bandwidth than an amplifier for a single thermopile element of the same data rate. The higher bandwidth would typically result in a much worse SN ratio than a narrower bandwidth amplifier for a single thermopile element. While the performance of a multiplexed pixel might be acceptable if only imaging is desired, it will degrade accuracy of a calculation of temperature at that pixel. Because single spot noncontact thermometers generally require high accuracy, the performance of a multiplexed pixel will typically be unacceptable for this purpose. 
     Thus, referring to  FIG. 7 , embodiments of the present invention “isolate” one thermopile element and have an individual amplifier for such pixel with a lower, optimized bandwidth. Thus, the arrangement of  FIG. 6  is modified such that thermopile element  60   e  (also referred to as thermopile  11 ) is connected directly to an amplifier  68  rather than to multiplexer  62   b  (the output of which is connected to amplifier  64   b ). The outputs of both multiplexer  66  and amplifier  68  are used in producing the thermal image, but the output of amplifier  68  will have better a SN ratio. This, in turn, yields greater accuracy in the spot temperature calculation. Amplifier  68  may be incorporated into the electronic package of the thermopile detector or it may implemented off-chip as a separate component (as shown). 
     While  FIGS. 6 and 7  illustrate a 3×3 thermopile array for purposes of discussion, the principles of the present invention are generally more beneficial on a larger array. For example,  FIG. 8  shows a thermopile array having thirty-two rows and thirty-two columns (32×32). While the spot temperature can be taken at a single thermopile element having the same physical size as the others, this embodiment uses a larger center pixel for this purpose. As can be seen, the center pixel in this example occupies the “real estate” of 2×2 regular thermopiles. Such an embodiment is believed to enhance SN ratio. 
     Alternatively, the array may be configured so that the spot temperature is determined from the output of multiple thermopiles. For example, multiple thermopiles in the center (e.g. 2×2), each having the same size as all other thermopiles on the array, may be connected together to provide a single output. In this regard, the multiple thermopiles may be wired in series to provide a higher output signal. Such wiring can be done on the array so that the series of those center thermopiles has only a single output to an amplifier, or it can be done outside (in which case each of those pixels would need outputs available outside of the array to allow for wiring together). This embodiment might be advantageous if a thermopile technology is optimized for a certain pixel size, so that a larger center pixel would cause problems and a lower yield in the manufacturing process. 
     While the spot measurement pixels will typically be in the center of the array, they need not be located in the center depending on the exigencies of a particular application. 
     It can thus be seen that the present invention provides a portable IR thermometer with accurate location temperature measurement and thermal imaging. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention as further described in the appended claims.