Patent Application
20170343418
Thermal cameras provide a non-contact, non-destructive measurement of wide-range temperature variations. However, measurements of absolute temperatures from thermal cameras have a relatively high degree of uncertainty, caused by both atmospheric conditions between the thermal camera and the object being measured, and the object's surface spectral/angular emissivity signature. Previous solutions include separately measuring a blackbody reference by itself or in conjunction with auxiliary reflecting surfaces standardized with respect to texture and material. Such procedures are used to calibrate the thermal camera for the atmospheric conditions and object emissivity, before measuring the object. However, these solutions require time consuming calibration steps, and only provide calibration for local atmospheric conditions.
To address the issues discussed above, an apparatus for use in measuring a temperature of a device under testing is provided. The apparatus comprising a palette body, a plurality of heat distribution plates mounted on the body and positioned adjacent each other, a plurality of insulators positioned intermediate the adjacently positioned heat distribution plates, and a plurality of thermal camera calibration reference swatches including a near-ideal blackbody reference swatch, a diffuse reflective reference swatch, and a first material of the device under testing reference swatch, each reference swatch being mounted on a corresponding one of the heat distribution plates and thermally insulated from other reference swatches by the insulators.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.
The computing device 18 includes a processor 19 configured to receive a thermal image 20 of the device under testing 14 and the palette body 16 from the thermal camera 12. The thermal image 20 include thermal data for each focal plane array “pixel” of the thermal camera, or for each image element acquired by a particular infrared imaging scanning sensor location of the thermal camera during its scanning excursion. After receiving the thermal image 20, the processor is configured to measure a temperature of the device under testing and the palette body 16 based on the thermal image.
Typically, absolute temperature signals measured using a thermal camera have a degree of uncertainty caused by several different factors, such as, for example, atmospheric and surface conditions including composition and texture of ambient air and of local infrared light emitting surfaces; surrounding environmental objects and materials and their temperatures; and the spectral/directional emissivities and reflectances of those environmental features as well as of the device under testing 14. These factors may cause thermal imaging using a thermal camera to exhibit both variations and fixed uncertainties in temperature readings larger than one degree Celsius, for the same device under testing (DUT) temperature and under different atmospheric and/or other environmental conditions; or across different DUT materials, even under identical temperature, atmospheric, and other environmental conditions.
Examples of the factors discussed above are illustrated in
In the illustrated example, photons P2 have collided with air molecules or particulates in the atmosphere A, and have had their direction altered from the path of photons P1. Thus these photons do not arrive at the correct (or sometimes any) pixel well of the thermal camera. Thus, the thermal camera will measure, at that particular pixel well, a different (smaller in the illustrated example) number of photons over the integration time period than are actually emitted from the surface element of the device under testing 14 being viewed by that pixel well. Similar errors may be caused at each pixel well of the thermal camera. Photon absorption always reduces the number of counted photons in any pixel well. These are some ways in which the absolute temperature of the device under testing 14, as measured by the thermal camera 12, will be affected by the atmosphere A. These scenarios of molecules or particulates in the atmosphere absorbing or scattering (redirecting) photons away from particular pixel wells in the device under testing 14 are examples of subtractive temperature offset errors that may occur in the thermal camera's 12 measurement of the device under testing 14.
Similarly to the processes discussed above, any photons originating in objects other than the device under testing 14, including air molecules or particulates, will appear to be originating from some imaged surface element of the device under testing 14 from the perspective of the thermal camera 12, provided the last leg of the photon's path, even if the path includes multiple redirections, is directed from that surface element of the device under testing 14 towards the camera optics of the thermal camera 12, and will then cause additive temperature offset errors.
The additive temperature offset errors discussed above occur when additive photons are emitted from a surface or object other than the device under testing 14. On the other hand, a multiplicative temperature error will occur when photons emitted by the device under testing 14, are deflected off other objects multiple times, before being directed back towards the thermal camera 12 from its source surface element on device under testing 14. In the illustrated example, the photons P4 are emitted from the device under testing 14 and are deflected off the wall WALL2 as photons P5. The photons P5 are then deflected from the original (emitting) surface element on device under testing 14, towards the thermal camera 12, and therefore appear to originate from the same surface element of the device-under-testing 14 from whence the primary photons P1 are being emitted. Consequently, as the photons P4 originated from the device under testing 14 itself, these photons will cause a multiplicative temperature error proportional to the actual absolute temperature of the device under testing 14. That is, as the actual temperature of the device under testing 14 increases, the multiplicative temperature error caused by photons such as photons P4 will also proportionally increase. This is also true of subtractive photon-count errors, but subtractive errors reduce photon counts whereas multiplicative errors increase them. It will be appreciated that the depicted and described examples of multipath errors are merely illustrative, and other multipath errors, not specifically discussed above, may also be corrected by the temperature measurement system 10.
In addition to the temperature measurement errors discussed above, an error in the temperature measurement of the device under testing 14 by the thermal camera 12 may be caused by inaccurate prior knowledge of spectral emissivity of the surface materials of the device under testing 14 in the spectral bands to which the thermal camera is sensitive. It will be appreciated that the device under testing 14 will emit only a fraction of the infrared light that an ideal blackbody would emit in any given spectral band to which thermal camera 12 is sensitive, and it will be further appreciated that this fraction is imperfectly known before use of the system and method herein described. This is equivalent to a level of uncertainty in the spectral emissivity of the device under testing in the relevant IR bands. Consequently, the thermal camera 12 only measures a portion of the electromagnetic radiation that would be emitted from the device under testing 14 in the sensitivity bands of camera 12 if the DUT were an ideal blackbody at the same temperature. Had the spectral emissivity of the surface materials of the device under testing 14 been accurately known in these sensitivity bands, the absolute temperature of the device under testing 14 could be calculated (absent the other types of errors described above) by suitably increasing the photon-count measurements of thermal camera 12. This type of emissivity correction is well known to those skilled in the art. However, any inaccuracies in the prior assumed knowledge of the spectral emissivity of the surface material of the device under testing 14 will cause an error in the above calculation.
To correct the possible errors caused by the photon-count error categories discussed above,
The first material of the device under testing reference swatch 26C includes the same type, or suitable representative type, of external-surface material used in the device under testing 14. If the device under testing 14 is constructed of multiple surface materials and/or textures, a single particular material of the device under testing 14 may be selected for the first material of the device under testing reference swatch 26C. The diffuse reflective reference swatch 26B may include a crumpled reflective material, or any other suitable diffuse reflective material.
In one embodiment, the plurality of heat distribution plates 22 include material having a high thermal conductivity such that each heat distribution plate 22 is configured to evenly distribute heat for the corresponding mounted thermal camera calibration reference swatches 26A-D. For example, the plurality of heat distribution plates may include material such as copper, a carbon material such as graphite or graphene, or any other suitable material having a high thermal conductivity. Thus, in this embodiment, the plurality of heat distribution plates 22 may efficiently distribute heat to and among the mounted reference swatches to minimize any temperature gradients along the mounted reference swatches.
In the embodiment illustrated in
As discussed above, the plurality of thermal camera calibration reference swatches includes a first material of the device under testing reference swatch 26C. In one embodiment, the plurality of thermal camera calibration reference swatches further includes a plurality of the first material of the device under testing reference swatches. Thus, in the depicted embodiment, both reference swatch 26C and 26D include the first material of the device under testing. However, it will be appreciated that the plurality of thermal camera calibration reference swatches may include more than four reference swatches, and thus may include any suitable number of the first material of the device under testing reference swatches. In another embodiment, the plurality of thermal camera calibration reference swatches 26A-D further includes a second material of the device under testing reference swatch that is different from the first material. As discussed above, the device under testing 14 may include more than one type of surface material. Thus, a second material different from the first material of the device under testing 14 may be selected and included in a reference swatch mounted on the palette body 16, such as reference swatch 26D. However, it will be appreciated that any number of different types of materials from the device under testing 14 may be included among the plurality of thermal camera calibration reference swatches.
Now turning to
The embodiment illustrated in
Turning back to
As discussed previously and illustrated in
In another embodiment, temperature measurement errors due to inaccurate prior knowledge of spectral emissivity of the surface materials of the device under testing 14 may be corrected based on the measured temperature of the first material of the device under testing reference swatch. It will be appreciated that because the first material of the device under testing reference swatch may comprise a primary surface material of the DUT 14 that constitutes a majority of the external surface of the DUT 14, the first material of the device under testing reference swatch may have the same or substantially similar spectral emissivity characteristics in the relevant bands, as does the surface of the DUT 14. Thus, by comparing the known predetermined temperature of the first material of the device under testing reference swatch to the temperature as measured by thermal camera 12, any temperature measurement errors due to inaccurate knowledge of the spectral emissivity characteristics of the DUT 14 may be corrected accordingly.
In one configuration, the processor 19 of computing device 18 may be configured to execute a correction algorithm that includes arithmetical operations between acquired and digitized values of different pixels of the thermal image 20. The correction algorithms may also include arithmetical operations between acquired and digitized pixels values of thermal image 20, and known predetermined temperature settings of the plurality of thermal camera calibration reference swatches. In one example, the arithmetical operations among different pixel values may include ratios of differences arithmetical operations. In another example, the arithmetical operations include division operations that correct multiplicative photon-count errors such as the multiplicative temperature errors. In yet another example, the arithmetical operations include differencing operations that correct additive and subtractive photon-count errors such as the additive temperature offset errors and the subtractive temperature offset errors.
In one configuration, the device under testing 14 and the palette body 16 are orientated in a same direction O towards the thermal camera 12. As illustrated in
In addition, in the illustrated configuration of
Proceeding from step 602 to step 604, the method 600 may include positioning the device under testing and the palette body in adjacent locations and in a same orientation towards the thermal camera.
Advancing from step 604 to step 606, the method 600 may include heating the plurality of thermal camera calibration reference swatches to predetermined temperatures.
Proceeding from step 606 to step 608, the method 600 may include imaging both the device under testing and the palette body in a same image via a thermal camera.
Advancing from step 608 to step 610, the method 600 may include measuring a temperature of the device under testing and the plurality of thermal camera calibration reference swatches based on the thermal camera image.
Proceeding from step 610 to step 612, the method 600 may include correcting temperature measurement errors of the measured temperature of the device under testing based on measured temperatures of the plurality of thermal camera calibration reference swatches. In one embodiment, correcting the temperature measurement errors includes compensation of temperature measurement errors selected from the group consisting of photon absorption, photon redirection, photon scattering, photon reflection, and errors in prior knowledge of spectral emissivity of the device under testing.
In another embodiment, step 612 may contain one or more substeps 614, 616, 618, and 620. At substep 614, the method 600 may include correcting a subtractive temperature offset error based on measured temperatures of the plurality of thermal camera calibration reference swatches. At substep 616, the method 600 may include correcting a multipath error based on measured temperatures of the plurality of thermal camera calibration reference swatches. Substep 616 may include substeps 618 and 620. At substep 618, the method 600 may include correcting an additive temperature offset error based on measured temperatures of the plurality of thermal camera calibration reference swatches. At substep 620, the method 600 may include correcting a multiplicative temperature error based on measured temperatures of the plurality of thermal camera calibration reference swatches.
Advancing from step 612 to step 622, the method 600 may include outputting a corrected measured temperature of the device under testing.
It will be appreciated that the method steps described above may be performed using the algorithmic processes described throughout this disclosure.
In some embodiments, the methods and processes described herein may be tied to a computing system of one or more computing devices. In particular, such methods and processes may be implemented as a computer-application program or service, an application-programming interface (API), a library, and/or other computer-program product.
Computing system 900 includes a logic processor 902 volatile memory 903, and a non-volatile storage device 904. Computing system 900 may optionally include a display subsystem 906, input subsystem 908, communication subsystem 1000, and/or other components not shown in
Logic processor 902 includes one or more physical devices configured to execute instructions. For example, the logic processor may be configured to execute instructions that are part of one or more applications, programs, routines, libraries, objects, components, data structures, or other logical constructs. Such instructions may be implemented to perform a task, implement a data type, transform the state of one or more components, achieve a technical effect, or otherwise arrive at a desired result.
The logic processor may include one or more physical processors (hardware) configured to execute software instructions. Additionally or alternatively, the logic processor may include one or more hardware logic circuits or firmware devices configured to execute hardware-implemented logic or firmware instructions. Processors of the logic processor 902 may be single-core or multi-core, and the instructions executed thereon may be configured for sequential, parallel, and/or distributed processing. Individual components of the logic processor optionally may be distributed among two or more separate devices, which may be remotely located and/or configured for coordinated processing. Aspects of the logic processor may be virtualized and executed by remotely accessible, networked computing devices configured in a cloud-computing configuration. In such a case, it will be understood that these virtualized aspects are run on different physical logic processors of various different machines.
Non-volatile storage device 904 includes one or more physical devices configured to hold instructions executable by the logic processors to implement the methods and processes described herein. When such methods and processes are implemented, the state of non-volatile storage device 94 may be transformed—e.g., to hold different data.
Non-volatile storage device 904 may include physical devices that are removable and/or built-in. Non-volatile storage device 94 may include optical memory (e.g., CD, DVD, HD-DVD, Blu-Ray Disc, etc.), semiconductor memory (e.g., ROM, EPROM, EEPROM, FLASH memory, etc.), and/or magnetic memory (e.g., hard-disk drive, floppy-disk drive, tape drive, MRAM, etc.), or other mass storage device technology. Non-volatile storage device 904 may include nonvolatile, dynamic, static, read/write, read-only, sequential-access, location-addressable, file-addressable, and/or content-addressable devices. It will be appreciated that non-volatile storage device 904 is configured to hold instructions even when power is cut to the non-volatile storage device 904.
Volatile memory 903 may include physical devices that include random access memory. Volatile memory 903 is typically utilized by logic processor 902 to temporarily store information during processing of software instructions. It will be appreciated that volatile memory 903 typically does not continue to store instructions when power is cut to the volatile memory 903.
Aspects of logic processor 902, volatile memory 903, and non-volatile storage device 904 may be integrated together into one or more hardware-logic components. Such hardware-logic components may include field-programmable gate arrays (FPGAs), program- and application-specific integrated circuits (PASIC/ASICs), program- and application-specific standard products (PSSP/ASSPs), system-on-a-chip (SOC), and complex programmable logic devices (CPLDs), for example.
The terms “module,” “program,” and “engine” may be used to describe an aspect of computing system 900 typically implemented in software by a processor to perform a particular function using portions of volatile memory, which function involves transformative processing that specially configures the processor to perform the function. Thus, a module, program, or engine may be instantiated via logic processor 902 executing instructions held by non-volatile storage device 904, using portions of volatile memory 903. It will be understood that different modules, programs, and/or engines may be instantiated from the same application, service, code block, object, library, routine, API, function, etc. Likewise, the same module, program, and/or engine may be instantiated by different applications, services, code blocks, objects, routines, APIs, functions, etc. The terms “module,” “program,” and “engine” may encompass individual or groups of executable files, data files, libraries, drivers, scripts, database records, etc.
When included, display subsystem 906 may be used to present a visual representation of data held by non-volatile storage device 904. The visual representation may take the form of a graphical user interface (GUI). As the herein described methods and processes change the data held by the non-volatile storage device, and thus transform the state of the non-volatile storage device, the state of display subsystem 906 may likewise be transformed to visually represent changes in the underlying data. Display subsystem 906 may include one or more display devices utilizing virtually any type of technology. Such display devices may be combined with logic processor 902, volatile memory 903, and/or non-volatile storage device 904 in a shared enclosure, or such display devices may be peripheral display devices.
When included, input subsystem 908 may comprise or interface with one or more user-input devices such as a keyboard, mouse, touch screen, microphone, camera, or game controller.
When included, communication subsystem 1000 may be configured to communicatively couple various computing devices described herein with each other, and with other devices. Communication subsystem 1000 may include wired and/or wireless communication devices compatible with one or more different communication protocols. As non-limiting examples, the communication subsystem may be configured for communication via a wireless telephone network, or a wired or wireless local- or wide-area network. In some embodiments, the communication subsystem may allow computing system 900 to send and/or receive messages to and/or from other devices via a network such as the Internet.
The following paragraphs provide additional support for the claims of the subject application. One aspect provides an apparatus for use in measuring a temperature of a device under testing, the apparatus comprising a palette body, a plurality of heat distribution plates mounted on the palette body and positioned adjacent each other, a plurality of insulators positioned intermediate the adjacently positioned heat distribution plates, and a plurality of thermal camera calibration reference swatches, including a near-ideal blackbody reference swatch, a diffuse reflective reference swatch, and a first material of the device under testing reference swatch, each reference swatch being mounted on a corresponding one of the heat distribution plates and thermally insulated from other reference swatches by the insulators. In this aspect, additionally or alternatively, the plurality of heat distribution plates may include material having a high thermal conductivity such that each heat distribution plate is configured to evenly distribute heat for the corresponding mounted thermal camera calibration reference swatch. In this aspect, additionally or alternatively, the plurality of thermal camera calibration reference swatches and corresponding heat distributions plates may be formed in a grid on the palette body. In this aspect, additionally or alternatively, the palette body and the plurality of thermal camera calibration references swatches may be planar. In this aspect, additionally or alternatively, the plurality of thermal camera calibration reference swatches may further include a plurality of the first material of the device under testing reference swatches. In this aspect, additionally or alternatively, the apparatus may further comprise a heat source configured to heat each of the plurality of thermal camera calibration reference swatches to predetermined temperatures, wherein each of the plurality of the first material of the device under testing reference swatches are heated to different predetermined temperatures. In this aspect, additionally or alternatively, the plurality of thermal camera calibration reference swatches may further include a second material of the device under testing reference swatch that is different from the first material. In this aspect, additionally or alternatively, each insulator may be formed as a divider wall laterally intermediate at least two of the plurality of thermal camera calibration reference swatches. In this aspect, additionally or alternatively, a height of each divider wall may be higher than surfaces of the plurality of thermal camera calibration reference swatches.
Another aspect provides a method comprising providing a palette body including a plurality of heat distribution plates mounted on the body and positioned adjacent each other, a plurality of insulators positioned intermediate the adjacently positioned heat distribution plates, a plurality of thermal camera calibration reference swatches including a near-ideal blackbody reference swatch, a diffuse reflective reference swatch, and a first material of the device under testing reference swatch, each reference swatch being mounted on a corresponding one of the heat distribution plates and thermally insulated from other reference swatches by the insulators, heating the plurality of thermal camera calibration reference swatches to predetermined temperatures, imaging both a device under testing and the palette body in a same image via a thermal camera, measuring a temperature of the device under testing and the plurality of thermal camera calibration reference swatches based on the thermal camera image, correcting temperature measurement errors of the measured temperature of the device under testing based on measured temperatures of the plurality of thermal camera calibration reference swatches, and outputting a corrected measured temperature of the device under testing. In this aspect, additionally or alternatively, correcting temperature measurement errors may include compensation of temperature measurement errors selected from the group consisting of photon absorption, photon redirection, photon scattering, photon reflecting, and errors in prior knowledge of spectral emissivity of the device under testing. In this aspect, additionally or alternatively, correcting temperature measurement errors may include correcting a subtractive temperature offset error based on measured temperatures of the plurality of thermal camera calibration reference swatches. In this aspect, additionally or alternatively, correcting temperature measurement errors may include correcting a multipath error based on measured temperatures of the plurality of thermal camera calibration reference swatches. In this aspect, additionally or alternatively, correcting multipath errors may include correcting an additive temperature offset error based on measured temperatures of the plurality of thermal camera calibration reference swatches. In this aspect, additionally or alternatively, correcting multipath errors may include correcting a multiplicative temperature error based on measured temperatures of the plurality of thermal camera calibration reference swatches. In this aspect, the method may additionally or alternatively include, positioning the device under testing and the palette body in adjacent locations and in a same orientation towards the thermal camera.
Another aspect provides a temperature measurement system comprising a thermal camera, a device under testing, and a palette body including a plurality of heat distribution plates mounted on the body and positioned adjacent each other, a plurality of insulators positioned intermediate the adjacently positioned heat distribution plates, a plurality of thermal camera calibration reference swatches including a near-ideal blackbody reference swatch, a diffuse reflective reference swatch, and a first material of the device under testing reference swatch, each reference swatch being mounted on a corresponding one of the heat distribution plates and thermally insulated from other reference swatches by the insulators, a computing device including a processor configured to receive a thermal image including both the device under testing and the palette body from the thermal camera, measure a temperature of the device under testing and the plurality of thermal camera calibration reference swatches based on the thermal image, correct temperature measurement errors of the measured temperature of the device under testing based on measured temperatures of the plurality of thermal camera calibration reference swatches, and output a corrected measured temperature of the device under testing. In this aspect, additionally or alternatively, the device under testing and the palette body may be orientated in a same direction towards the thermal camera. In this aspect, additionally or alternatively, the palette body and the device under testing may be positioned at a first distance from the thermal camera, and the palette body and the plurality of thermal camera calibration reference swatches may have width and length dimensions that are less than 20% of the first distance. In this aspect, additionally or alternatively, the palette body and the device under testing may be positioned at a second distance from nearby walls, and the palette body and the plurality of thermal camera calibration reference swatches may have width and length dimensions that are less than 20% of the second distance.
It will be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated and/or described may be performed in the sequence illustrated and/or described, in other sequences, in parallel, or omitted. Likewise, the order of the above-described processes may be changed.
The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.
