Infrared thermal imaging device for wide temperature measurement range and design method thereof

Abstract

The present application relates to the technical field of infrared temperature measurement, and particularly relates to an infrared thermal imaging device for wide temperature measurement range and a design method thereof. The design method comprises: setting a full-pass plane mirror with an average infrared spectrum transmittance of 1 between a front-end optical system and a rear-end infrared detector; establishing a linear relationship among the average infrared spectrum transmittance, the radiation temperature and the total response gray scale; determining a lower limit temperature corresponding to a lower limit of the response gray scale of the full-pass plane mirror and an upper limit temperature corresponding to an upper limit of the response gray scale according to the linear relationship; designing at least one attenuation plane mirror for the infrared spectrum between the front-end optical system and the rear-end infrared detector; taking the upper limit temperature corresponding to the full-pass plane mirror as a lower limit temperature corresponding to the attenuation plane mirror, and calculating the average infrared spectrum transmittance of the attenuation plane mirror and the upper limit temperature corresponding to the attenuation plane mirror according to the linear relationship. The present application can measure temperature in a wide range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of infrared temperature measurement technology, in particular to an infrared thermal imaging device for wide temperature measurement range and a design method thereof. BACKGROUND

[0002] With the development of infrared detectors, more and more occasions require non-contact remote temperature measurement. Generally, a temperature measurement thermal imager can only measure the temperature in a relatively narrow temperature range such as human body. The hand-held temperature measurement thermal imager used in the market mostly adopts a long-wave uncooled chip, which has poor response linearity and limited temperature measurement range, generally up to hundreds of degrees Celsius.

[0003] In addition, with the development of decoy technology, the anti-interference ability and the true and false target recognition ability of the infrared detection system are required to be higher and higher. The existing infrared system can only obtain non-quantitative infrared images, and only relying on motion characteristics and imaging characteristics cannot effectively identify true and false targets. The latest target recognition technology also needs to rely on the radiation characteristics of the target. This requires an infrared thermal imaging device that can meet the high temperature measurement range and has the ability of quantitative measurement of infrared radiation, combined with target recognition technology, to enhance the infrared detection capability. SUMMARY

[0004] The embodiment of the present application provides an infrared thermal imaging device for wide temperature measurement range and a design method thereof, which can measure temperature in a wide range.

[0005] In the first aspect, the embodiment of the present application provides a design method of an infrared thermal imaging device for wide temperature measurement range, comprising:

[0006] An all-pass mirror with an average infrared spectral transmittance of 1 is arranged between the front-end optical system and the rear-end infrared detector;

[0007] A linear relationship between the average infrared spectral transmittance, the radiation temperature and the total response gray scale is established; wherein the total response gray scale range includes a lower limit of response gray scale and an upper limit of response gray scale;

[0008] The lower limit temperature corresponding to the lower limit of response gray scale of the all-pass mirror and the upper limit temperature corresponding to the upper limit of response gray scale are determined according to the linear relationship;

[0009] At least one attenuation mirror for infrared spectrum is designed between the front-end optical system and the rear-end infrared detector;

[0010] The upper limit temperature corresponding to the all-pass mirror is taken as the lower limit temperature corresponding to the attenuation mirror, and the average infrared spectral transmittance of the attenuation mirror and the upper limit temperature corresponding to the attenuation mirror are calculated according to the linear relationship;

[0011] For each lower limit temperature and upper limit temperature corresponding to an attenuation flat mirror, the following is performed: determining whether the highest temperature to be measured is between the lower limit temperature and the upper limit temperature corresponding to the attenuation flat mirror, if not, adding an attenuation flat mirror, taking the upper limit temperature corresponding to the attenuation flat mirror as the lower limit temperature corresponding to the newly added attenuation flat mirror, calculating the average infrared spectral transmittance of the newly added attenuation flat mirror and the upper limit temperature corresponding to the newly added attenuation flat mirror according to the linear relationship, and if yes, stopping adding the attenuation flat mirror.

[0012] In a possible design, the linear relationship between the average infrared spectral transmittance, the radiation brightness, and the response gray scale range is established by:

[0013] A radiation brightness formula between the blackbody temperature and the blackbody radiation brightness is established by using the Planck formula;

[0014] The range of the radiation measure and the total gray scale of the thermal imager response is obtained, linear fitting is performed, and the linear relationship is obtained.

[0015] In a possible design, the radiation brightness formula is as follows:

[0016]

[0017] Wherein, L is the spectral radiation brightness, λ is the wavelength, λ1 and λ2 are the cut-off wavelengths of the infrared thermal imaging device imaging spectrum, C1 is the first radiation constant, C2 is the second radiation constant, and T is the absolute temperature.

[0018] In a possible design, the linear relationship is as follows:

[0019] G(T)=aτL(T)+b

[0020] Wherein, G is the response gray scale, a and b are fitting coefficients, L is the spectral radiation brightness, τ is the average infrared spectral transmittance, and T is the absolute temperature.

[0021] In a possible design, the total gray scale of the response is determined in the following manner:

[0022] The digital image gray scale response of the infrared thermal imaging device is obtained by adjusting different blackbody temperatures.

[0023] The total gray scale of the digital image response is determined according to the number of bits of the digital image.

[0024] In a possible design, the following is further included:

[0025] The lower limit of the response gray scale and the upper limit of the response gray scale are determined according to the total gray scale of the response and the linearity of the radiation brightness.

[0026] In a second aspect, the embodiments of the present application also provide an infrared testing device for wide temperature measurement range, which is designed according to any of the above methods, and comprises a front optical system, a rear infrared detector and a rotating filter wheel.

[0027] The rotating filter wheel is arranged between the front optical system and the rear infrared detector, and sequentially comprises one full-pass plane mirror and at least one attenuation plane mirror along the circumference, the number and the average infrared spectral transmittance of each attenuation plane mirror are determined by any of the above methods, and the rotating filter wheel is used to pass the light spot output by the front optical system through different full-pass plane mirrors or attenuation plane mirrors by rotation, so as to realize temperature measurement in different temperature intervals.

[0028] In a possible design, the position of each plane mirror of the rotating filter wheel ensures that the light passing surface of each plane mirror on the filter wheel can pass the light spot completely, and does not block the light passing through the field of view, and when each filter wheel plane mirror is switched, the target and the scene are clearly imaged in the optical path system; wherein the plane mirror comprises a full-pass plane mirror and an attenuation plane mirror.

[0029] In a possible design, the thickness of all the plane mirrors is the same.

[0030] In a possible design, when the filter wheel switches different plane mirrors, the integration time is unchanged.

[0031] Compared with the prior art, the present application has at least the following beneficial effects:

[0032] In the embodiment, a full-pass plane mirror with an average infrared spectrum transmittance of 1 is arranged between the front-end optical system and the rear-end infrared detector, so that the infrared light completely transmits through the full-pass plane mirror. Then, a linear relationship between the average infrared spectrum transmittance, the radiation temperature and the total gray scale is established, and the third item can be obtained by using the linear relationship and any two known items. The instrument has a range of gray scale response to different temperatures, that is, the instrument can measure the corresponding temperature through the gray scale response. If the temperature exceeds the range of total gray scale response, accurate temperature measurement cannot be realized. In the case that the upper limit of the response gray scale and the lower limit of the response gray scale are known, the average infrared spectrum transmittance of the full-pass plane mirror is 1, so the lower limit temperature corresponding to the lower limit of the response gray scale of the full-pass plane mirror and the upper limit temperature corresponding to the upper limit of the response gray scale can be obtained respectively by using the linear relationship. In order to increase the temperature measurement range, an attenuation plane mirror is designed. The attenuation plane mirror can attenuate the infrared light, so that the infrared light released by the higher temperature can be attenuated through the attenuation plane mirror, and the corresponding gray scale response can still be obtained. In order to make the temperature measurement range continuous, the average infrared spectrum transmittance of the attenuation plane mirror is first regarded as an unknown number. After the attenuation plane mirror is arranged, the lower limit temperature measured at the lower limit of the response gray scale is the upper limit temperature measured by the full-pass plane mirror. Thus, the lower limit temperature of the attenuation plane mirror is known, and the lower limit of the response gray scale is known, so the average infrared spectrum transmittance of the attenuation plane mirror can be obtained. Then, the upper limit temperature of the attenuation plane mirror is obtained according to the average infrared spectrum transmittance of the attenuation plane mirror and the upper limit of the response gray scale. Thus, the width of the temperature measurement is increased. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0034] Figure 1 is a structural schematic diagram of an infrared thermal imaging device for wide temperature measurement range provided by the embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0036] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the terms "first", "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance; unless otherwise specified or stated, the term "multiple" refers to two or more than two; the terms "connection", "fixation" and the like should be understood in a broad sense, for example, "connection" can be fixed connection, or detachable connection, or integrally connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0037] In the description of the present specification, it should be understood that the "upper", "lower" and the like described in the embodiments of the present application are described with the angle shown in the drawings, and should not be understood as limiting the embodiments of the present application. In addition, in the context, it should also be understood that when referring to one element connected to another element "on" or "below", it can not only be directly connected to another element "on" or "below", but also indirectly connected to another element "on" or "below" through an intermediate element.

[0038] The embodiments of the present application provide a design method of an infrared thermal imaging device for a wide temperature measurement range, comprising:

[0039] An all-pass mirror with an average infrared spectral transmittance of 1 is arranged between the front optical system and the rear infrared detector;

[0040] A linear relationship between the average infrared spectral transmittance, the radiation temperature and the total response gray scale is established; wherein the total response gray scale range includes the lower limit of response gray scale and the upper limit of response gray scale;

[0041] The lower limit temperature corresponding to the lower limit of response gray scale and the upper limit temperature corresponding to the upper limit of response gray scale of the all-pass mirror are determined according to the linear relationship;

[0042] At least one attenuation mirror for infrared spectrum is designed between the front optical system and the rear infrared detector;

[0043] The upper limit temperature corresponding to the all-pass mirror is taken as the lower limit temperature corresponding to the attenuation mirror, and the average infrared spectral transmittance of the attenuation mirror and the upper limit temperature corresponding to the attenuation mirror are calculated according to the linear relationship;

[0044] Each time a lower limit temperature and an upper limit temperature corresponding to an attenuation plane mirror are obtained, the following is performed: it is determined whether the highest temperature to be measured is between the lower limit temperature and the upper limit temperature corresponding to the attenuation plane mirror, if not, an attenuation plane mirror is added, the upper limit temperature corresponding to the attenuation plane mirror is taken as the lower limit temperature of the newly added attenuation plane mirror, the average infrared spectral transmittance of the newly added attenuation plane mirror and the upper limit temperature corresponding to the newly added attenuation plane mirror are calculated according to the linear relationship, and if yes, the addition of the attenuation plane mirror is stopped.

[0045] In the present embodiment, a full-pass mirror with an average infrared spectral transmittance of 1 is arranged between the front-end optical system and the rear-end infrared detector, so that the infrared light completely transmits through the full-pass mirror. Then, a linear relationship between the average infrared spectral transmittance, the radiation temperature and the total gray scale response is established, and the third item can be calculated by using the linear relationship with any two known items. The instrument has a range of gray scale response to different temperatures, that is, the instrument can measure the corresponding temperature through the gray scale response, and if the temperature exceeds the total gray scale response range, the accurate temperature measurement cannot be realized. In the case where the upper limit of the response gray scale and the lower limit of the response gray scale are known, the average infrared spectral transmittance of the full-pass mirror is 1, and therefore, the lower limit temperature corresponding to the lower limit of the response gray scale of the full-pass mirror and the upper limit temperature corresponding to the upper limit of the response gray scale can be respectively calculated by using the linear relationship. In order to increase the temperature measurement range, an attenuation plane mirror is designed, which can attenuate the infrared light, so that the infrared light released by a higher temperature can be attenuated through the attenuation plane mirror, and the corresponding gray scale response can still be obtained. In order to make the temperature measurement range continuous, the average infrared spectral transmittance of the attenuation plane mirror is first taken as an unknown number, and then the lower limit temperature of the temperature measurement at the lower limit of the response gray scale is limited to be the upper limit temperature of the temperature measurement of the full-pass mirror. Thus, the lower limit temperature of the attenuation plane mirror and the lower limit of the response gray scale are known, and the average infrared spectral transmittance of the attenuation plane mirror can be calculated. Then, the upper limit temperature of the attenuation plane mirror is calculated according to the average infrared spectral transmittance of the attenuation plane mirror and the upper limit of the response gray scale. Thus, the temperature measurement width is increased.

[0046] It can be understood that multiple attenuation plane mirrors can be added to further increase the temperature measurement width. In the case where the temperature measurement requirement is known, an infrared tester for the temperature measurement requirement can be flexibly designed. According to the temperature measurement requirement, the highest temperature to be measured is determined, and when each attenuation plane mirror is added, it is determined whether the highest temperature to be measured is between the upper limit temperature and the lower limit temperature of the attenuation plane mirror, if yes, the requirement is met, and if not, a new attenuation plane mirror is continuously added, the upper limit temperature of the attenuation plane mirror is taken as the lower limit temperature of the newly added attenuation plane mirror, and the average infrared spectral transmittance and the upper limit temperature of the newly added attenuation plane mirror are calculated according to the linear relationship combined with the known lower limit of the response gray scale and the upper limit of the response gray scale.

[0047] In some embodiments of the present application, the linear relationship between the average infrared spectral transmittance, the radiation luminance and the response grayscale range is established, comprising:

[0048] The radiation luminance formula between the blackbody temperature and the blackbody radiation luminance is established by using Planck formula;

[0049] The radiation measurement and the range of total grayscale of the thermal imager response are obtained, linear fitting is performed to obtain the linear relationship.

[0050] In the present embodiment, the radiation luminance corresponding to different blackbody temperatures is calculated by using Planck formula, since the output level of the thermal imager is proportional to the blackbody radiation luminance, in order to facilitate comparison, the blackbody temperature is first converted into blackbody radiation luminance according to Planck formula.

[0051] In some embodiments of the present application, the radiation luminance formula is as follows:

[0052]

[0053] Wherein, L is spectral radiation luminance (W·cm· / Sr), λ is wavelength (μm), λ1 and λ2 are the cut-off wavelengths of the infrared thermal imaging device imaging spectrum (μm), C1 is the first radiation constant = 3.7415×10 4 (W·cm -2 ·μm 4 ), C2 is the second radiation constant = 1.4388×10 4 (μm·K), T is absolute temperature (K).

[0054] In some embodiments of the present application, the linear relationship is as follows:

[0055] G(T)=aτL(T)+b

[0056] Wherein, G is response grayscale, a and b are fitting coefficients, L is spectral radiation luminance, τ is average infrared spectral transmittance, and T is absolute temperature.

[0057] In the present embodiment, for the full-pass mirror, the channel of the light passing through the full-pass mirror is set as channel 1, the grayscale response lower limit G k1 and the upper limit G k2 corresponding to the temperature are respectively the lower limit temperature T 11 and the upper limit temperature T 12 of channel 1 temperature measurement, wherein the two numbers behind T represent the channel number and the upper limit and lower limit of temperature.

[0058] The lower limit temperature T 11 and the upper limit temperature T 12Afterwards, the transmittance of the attenuating flat mirror, the upper limit temperature and the lower limit temperature are calculated. The number of the channel where the first attenuating flat mirror is located is 2, and the numbers of the channels where the subsequent added attenuating flat mirrors are located are added in sequence. Let T 21 = T 12 , the average transmittance τ2 of the channel 2 attenuating piece can be determined, and the number after the symbol τ of the transmittance is the channel number. Specifically, the formula

[0059]

[0060] is used to obtain the transmittance τ2.

[0061] Then the formula

[0062] G k1 = aτ2L(T 22 ) + b

[0063] is used to inversely calculate the upper limit temperature T 22 .

[0064] The above steps are repeated, and the lower limit temperature T i1 and the upper limit temperature T i2 of the channels 3 to N and the average transmittance τ i (i = 3…N) of the attenuating pieces are obtained. Finally, the highest temperature T max to be measured is ensured to meet the requirement T N1 < T max < T N2 , and the step is repeated until the end, the number N of the channels of the filter wheel is determined, and N-1 is the number of the attenuating flat mirrors.

[0065] In some embodiments of the present application, the total gray scale response is determined as follows:

[0066] The digital image gray scale response of the infrared thermal imaging device is obtained by adjusting different blackbody temperatures.

[0067] The total digital image gray scale response is determined according to the number of bits of the digital image.

[0068] Specifically, a fixed integration time is determined, and then the infrared thermal imaging device is directed at the blackbody, and the digital image gray scale response of the infrared thermal imaging device is obtained by adjusting different blackbody temperatures.

[0069] The total digital image gray scale response is determined by the number of bits collected. For an M-bit digital image, the total digital image gray scale response is 2 M -1.

[0070] In some embodiments of the present application, the following are further included:

[0071] The lower limit of the response gray scale and the upper limit of the response gray scale are determined according to the total gray scale and the linearity of the radiation brightness.

[0072] The lower limit ratio k1 and the upper limit ratio k2 of the gray scale response can be selected according to the current linearity of the detector, and for the gray scale response and the brightness linearity in the full dynamic response range, k1 can be selected as 10% to 20%, and k2 can be selected as 80% to 90%. For the gray scale response and the brightness linearity in the full dynamic response range, k1 and k2 are selected in the range in which the middle linear response is better.

[0073] As shown in FIG. 1, Figure 1 The embodiment of the present application also provides an infrared testing device for a wide temperature measurement range, which is designed according to any of the above methods, and the device comprises a front-end optical system, a rear-end infrared detector and a rotating filter wheel.

[0074] The rotating filter wheel is arranged between the front-end optical system and the rear-end infrared detector, one full-pass plane mirror and at least one attenuation plane mirror are sequentially arranged in the rotating filter wheel in the circumferential direction, the number of the attenuation plane mirrors and the average infrared spectral transmittance of each attenuation plane mirror are determined by any of the above methods, and the rotating filter wheel is used to make the light spot output by the front-end optical system pass through different full-pass plane mirrors or attenuation plane mirrors by rotation, so that the temperature measurement in different temperature intervals is realized.

[0075] In some embodiments of the present application, the position of each plane mirror of the rotating filter wheel ensures that the light passing surface of each plane mirror in the filter wheel can completely pass through the passing light spot, and does not block the light passing through the field of view angle; when each filter wheel plane mirror is switched, the target and the scene are clearly imaged in the optical path system; wherein the plane mirror comprises a full-pass plane mirror and an attenuation plane mirror.

[0076] In some embodiments of the present application, the thicknesses of all the plane mirrors are the same.

[0077] In some embodiments of the present application, the integration time is unchanged when the filter wheel switches different plane mirrors.

[0078] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A design method for an infrared thermal imaging device with a wide temperature measurement range, characterized in that, include: A fully transparent plane mirror with an average infrared spectral transmittance of 1 is placed between the front-end optical system and the back-end infrared detector; A linear relationship is established between average infrared spectral transmittance, radiation temperature, and total gray level of response; wherein, the range of total gray level of response includes the lower limit and the upper limit of gray level of response. Based on the linear relationship, determine the lower limit temperature corresponding to the lower limit of the grayscale response of the full-pass plane mirror and the upper limit temperature corresponding to the upper limit of the grayscale response. Design at least one attenuating plane mirror for the infrared spectrum between the front-end optical system and the back-end infrared detector; The upper limit temperature corresponding to the full-pass plane mirror is taken as the lower limit temperature corresponding to the attenuation plane mirror. The average infrared spectral transmittance of the attenuation plane mirror and the upper limit temperature corresponding to the attenuation plane mirror are calculated according to the linear relationship. For each attenuation plane mirror whose lower and upper limits of temperature are obtained, the following steps are performed: determine whether the highest temperature to be measured is between the lower and upper limits of the attenuation plane mirror; if not, add an attenuation plane mirror, take the upper limit of the attenuation plane mirror as the lower limit of the newly added attenuation plane mirror, calculate the average infrared spectral transmittance of the newly added attenuation plane mirror and the upper limit of the newly added attenuation plane mirror according to the linear relationship; if yes, stop adding attenuation plane mirrors.

2. The method according to claim 1, characterized in that, The establishment of the linear relationship between average infrared spectral transmittance, radiance, and response grayscale range includes: A formula for the radiance between blackbody temperature and blackbody radiance is established using Planck's formula. The ranges of radiance and total grayscale of thermal imager response are obtained, and linear fitting is performed to obtain the linear relationship.

3. The method according to claim 2, characterized in that, The formula for radiance is as follows: Where L is the spectral radiance, λ is the wavelength, λ1 and λ2 are the cutoff wavelengths of the imaging spectrum of the infrared thermal imaging device, C1 is the first radiation constant, C2 is the second radiation constant, and T is the absolute temperature.

4. The method according to claim 1, characterized in that, The linear relationship is as follows: G(T)=aτL(T)+b Where G is the response gray level, a and b are fitting coefficients, L is the spectral radiance, τ is the average infrared spectral transmittance, and T is the absolute temperature.

5. The method according to claim 1, characterized in that, The total grayscale of the response is determined in the following way: The grayscale response of digital images from an infrared thermal imaging device is obtained by adjusting different blackbody temperatures. The total gray level of the digital image response is determined based on the number of bits in the digital image.

6. The method according to claim 1, characterized in that, Also includes: The lower limit and upper limit of the response gray level are determined based on the linearity of the total gray level and radiance of the response.

7. An infrared testing device for a wide temperature measurement range, characterized in that, The device, designed according to any one of claims 1-6, comprises a front-end optical system, a rear-end infrared detector, and a rotating filter wheel; The rotating filter wheel is disposed between the front-end optical system and the rear-end infrared detector. The rotating filter wheel is provided with a full-pass plane mirror and at least one attenuating plane mirror in sequence along the circumference. The number of attenuating plane mirrors and their average infrared spectral transmittance are determined by any of the methods in claims 1-6. The rotating filter wheel is used to rotate so that the light spot output by the front-end optical system passes through different full-pass plane mirrors or attenuating plane mirrors to achieve temperature measurement in different temperature ranges.

8. The infrared testing device according to claim 7, characterized in that, The position of each plane mirror on the rotating filter wheel ensures that the light-transmitting surface of each plane mirror on the filter wheel can completely pass through the passing light spot without blocking the light passing through the person and the field of view. When switching each plane mirror on the filter wheel, the target and the scene are clearly imaged in the optical path system. The plane mirrors include full-pass plane mirrors and attenuation plane mirrors.

9. The infrared testing device according to claim 8, characterized in that, All the plane mirrors have the same thickness.

10. The infrared testing device according to claim 8, characterized in that, When the filter wheel switches between different plane mirrors, the integration time remains unchanged.

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