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

Abstract

The invention relates to the technical field of infrared temperature measurement, in particular to an infrared thermal imaging device for a wide temperature measurement range and a design method of the infrared thermal imaging device. The design method comprises the steps that an all-pass plane mirror with the average infrared spectrum transmittance being 1 is arranged between a front-end optical system and a rear-end infrared detector; establishing a linear relation among the average infrared spectrum transmittance, the radiation temperature and the response total gray scale; determining the lower limit temperature corresponding to the response gray lower limit and the upper limit temperature corresponding to the response gray upper limit of the all-pass plane mirror according to the linear relation; at least one attenuation plane mirror for an infrared spectrum is designed between the front-end optical system and the rear-end infrared detector; and taking the upper limit temperature corresponding to the all-pass plane mirror as the 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 relation. According to the scheme, wide-range temperature measurement can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of infrared temperature measurement, and in particular to an infrared thermal imaging device for a wide temperature measurement range and a design method thereof. Background Art

[0002] With the development of infrared detectors, non-contact remote sensing temperature measurement is required in more and more occasions. Generally, thermal imagers can only measure the temperature of the human body within a relatively narrow temperature range. Most handheld thermal imagers used in the market use long-wave uncooled chips, which have poor response linearity and a limited temperature measurement range, generally up to hundreds of degrees Celsius.

[0003] In addition, with the development of jamming and decoy technology, the requirements for the anti-interference ability and true and false target identification ability of infrared detection systems are getting higher and higher. The existing infrared system can only obtain non-quantitative infrared images, and it can no longer effectively identify true and false targets by relying solely on motion characteristics and imaging characteristics. 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 a high temperature measurement range and has the ability to quantitatively measure infrared radiation, combined with target recognition technology, to enhance infrared detection capabilities. Summary of the invention

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

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

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

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

[0008] Determine the lower limit temperature corresponding to the lower limit of the grayscale response of the all-pass plane mirror and the upper limit temperature corresponding to the upper limit of the grayscale response according to the linear relationship;

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

[0010] Taking the upper limit temperature corresponding to the all-pass plane mirror as the 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;

[0011] Every time the lower limit temperature and upper limit temperature corresponding to an attenuation plane mirror are obtained, the following is performed: determining whether the maximum temperature to be measured is between the lower limit temperature and the upper limit temperature corresponding to the attenuation plane mirror; if not, adding an attenuation plane mirror, using the upper limit temperature corresponding to the attenuation plane mirror as the lower limit temperature corresponding to the newly added attenuation plane mirror, calculating 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 according to the linear relationship; if so, stopping adding the attenuation plane mirror.

[0012] In a possible design, the establishment of a linear relationship between average infrared spectrum transmittance, radiant brightness and response grayscale range includes:

[0013] Use Planck's formula to establish the radiation brightness formula between black body temperature and black body radiation brightness;

[0014] The range of the total grayscale of the radiation measurement and the thermal imager response is obtained, and linear fitting is performed to obtain the linear relationship.

[0015] In one possible design, the radiance 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 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.

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

[0019] G(T)=aτL(T)+b

[0020] Among them, G is the response grayscale, a and b are fitting coefficients, L is the spectral radiation brightness, τ is the average infrared spectrum transmittance, and T is the absolute temperature.

[0021] In one possible design, the total grayscale of the response is determined as follows:

[0022] Adjust different black body temperatures to obtain the grayscale response of the digital image of the infrared thermal imaging device;

[0023] Determine the total grayscale response of the digital image based on the number of bits of the digital image.

[0024] In one possible design, it also includes:

[0025] The lower limit and upper limit of the response grayscale are determined according to the total grayscale response and the linearity of the radiant brightness.

[0026] In a second aspect, an embodiment of the present invention further provides an infrared testing device for a wide temperature measurement range, which is designed according to any of the above methods, and the device includes a front-end optical system, a rear-end infrared detector and a rotating filter wheel;

[0027] The rotating filter wheel is arranged between the front-end optical system and the rear-end infrared detector. The rotating filter wheel is sequentially provided with an all-pass plane mirror and at least one attenuation plane mirror along the circumferential direction. The number of the attenuation plane mirrors and their respective average infrared spectral transmittances are determined by any of the above methods. The rotating filter wheel is used to rotate so that the light spot output by the front-end optical system passes through different all-pass plane mirrors or attenuation plane mirrors to achieve temperature measurement in different temperature ranges.

[0028] In a possible design, the position of each plane mirror of the rotating filter wheel ensures that the light-transmitting surface of each plane mirror on the filter wheel can completely pass the passing light spot without blocking the light passing through people and the field of view. When each plane mirror of the filter wheel is switched, the target and the scene are clearly imaged in the optical path system; wherein the plane mirrors include all-pass plane mirrors and attenuation plane mirrors.

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

[0030] In a possible design, when the filter wheel switches to a different plane mirror, the integration time remains unchanged.

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

[0032] In this embodiment, a full-pass plane mirror with an average infrared spectrum transmittance of 1 is set between the front-end optical system and the rear-end infrared detector, so that the infrared light can completely pass through the full-pass plane mirror. Then a linear relationship between the average infrared spectrum transmittance, the radiation temperature and the total grayscale of the response is established. The linear relationship can be used to obtain the third term through any two known terms. The instrument has a range of grayscale responses to different temperatures, that is, the instrument can measure the corresponding temperature through the grayscale response. If the temperature exceeds the total grayscale range of the response, accurate temperature measurement cannot be achieved. When the upper limit and lower limit of the grayscale response are known, the average infrared spectrum transmittance of the full-pass plane mirror is 1. Therefore, 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 can be obtained respectively through the linear relationship. In order to increase the temperature measurement range, an attenuation plane mirror is designed to be added. The attenuation plane mirror can attenuate infrared light, so that the infrared light released at a higher temperature is attenuated by the attenuation plane mirror, and the corresponding grayscale 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 set as an unknown number. After the attenuation plane mirror is set, the lower limit temperature of the temperature measured at the lower limit of the response grayscale is first limited to the upper limit temperature of the temperature measurement of the full-pass plane mirror. Therefore, if the lower limit temperature of the attenuation plane mirror is known and the lower limit of the response grayscale is known, the average infrared spectrum transmittance of the attenuation plane mirror can be calculated. Then, according to the obtained average infrared spectrum transmittance of the attenuation plane mirror and the upper limit of the response grayscale, the upper limit temperature of the attenuation plane mirror is calculated. In this way, the width of temperature measurement is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple" refers to two or more; the terms "connected" and "fixed" should be understood in a broad sense, for example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the description of this specification, it should be understood that the directional words such as "upper" and "lower" described in the embodiments of the present invention are described at the angles shown in the drawings and should not be understood as limiting the embodiments of the present invention. In addition, in the context, it should also be understood that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to another element "upper" or "lower", but also indirectly connected to another element "upper" or "lower" through an intermediate element.

[0038] An embodiment of the present invention provides a method for designing an infrared thermal imaging device for a wide temperature measurement range, comprising:

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

[0040] A linear relationship between the average infrared spectrum transmittance, the radiation temperature and the total grayscale response is established; wherein the total grayscale response range includes a lower grayscale response limit and an upper grayscale response limit;

[0041] Determine the lower limit temperature corresponding to the lower limit of the grayscale response of the all-pass plane mirror and the upper limit temperature corresponding to the upper limit of the grayscale response according to the linear relationship;

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

[0043] Taking the upper limit temperature corresponding to the all-pass plane mirror as the 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;

[0044] Every time the lower limit temperature and upper limit temperature corresponding to an attenuation plane mirror are obtained, the following is performed: determining whether the maximum temperature to be measured is between the lower limit temperature and the upper limit temperature corresponding to the attenuation plane mirror; if not, adding an attenuation plane mirror, using the upper limit temperature corresponding to the attenuation plane mirror as the lower limit temperature corresponding to the newly added attenuation plane mirror, calculating 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 according to the linear relationship; if so, stopping adding the attenuation plane mirror.

[0045] In this embodiment, a full-pass plane mirror with an average infrared spectrum transmittance of 1 is set between the front-end optical system and the rear-end infrared detector, so that the infrared light can completely pass through the full-pass plane mirror. Then a linear relationship between the average infrared spectrum transmittance, the radiation temperature and the total grayscale of the response is established. The linear relationship can be used to obtain the third term through any two known terms. The instrument has a range of grayscale responses to different temperatures, that is, the instrument can measure the corresponding temperature through the grayscale response. If the temperature exceeds the total grayscale range of the response, accurate temperature measurement cannot be achieved. When the upper limit and lower limit of the grayscale response are known, the average infrared spectrum transmittance of the full-pass plane mirror is 1. Therefore, 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 can be obtained respectively through the linear relationship. In order to increase the temperature measurement range, an attenuation plane mirror is designed to be added. The attenuation plane mirror can attenuate infrared light, so that the infrared light released at a higher temperature is attenuated by the attenuation plane mirror, and the corresponding grayscale 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 set as an unknown number. After the attenuation plane mirror is set, the lower limit temperature of the temperature measured at the lower limit of the response grayscale is first limited to the upper limit temperature of the temperature measurement of the full-pass plane mirror. Therefore, if the lower limit temperature of the attenuation plane mirror is known and the lower limit of the response grayscale is known, the average infrared spectrum transmittance of the attenuation plane mirror can be calculated. Then, according to the obtained average infrared spectrum transmittance of the attenuation plane mirror and the upper limit of the response grayscale, the upper limit temperature of the attenuation plane mirror is calculated. In this way, the width of temperature measurement is increased.

[0046] It is understandable that multiple attenuation plane mirrors can be added to further increase the temperature measurement width. In the case of known temperature measurement requirements, an infrared tester can be flexibly designed for the temperature measurement requirements. The maximum temperature to be measured is determined according to the temperature measurement requirements. When each attenuation plane mirror is added, it is determined whether the maximum temperature to be measured is between the upper and lower temperature limits of the attenuation plane mirror. If so, the requirement is met; if not, new attenuation plane mirrors are added, and the upper temperature limit of the attenuation plane mirror is used as the lower temperature limit of the newly added attenuation plane mirror. Combined with the known response grayscale lower limit and response grayscale upper limit, the average infrared spectral transmittance and upper temperature of the newly added attenuation plane mirror are calculated according to the linear relationship.

[0047] In some embodiments of the present invention, the step of establishing a linear relationship between the average infrared spectrum transmittance, the radiant brightness and the response grayscale range includes:

[0048] Use Planck's formula to establish the radiation brightness formula between black body temperature and black body radiation brightness;

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

[0050] In this embodiment, the Planck formula is used to calculate the radiation brightness corresponding to different blackbody temperatures. Since the output level of the thermal imager is proportional to the blackbody radiation brightness, for the convenience of comparison, the blackbody temperature is first converted into the blackbody radiation brightness according to the Planck formula.

[0051] In some embodiments of the present invention, the radiance formula is as follows:

[0052]

[0053] Where L is the spectral radiance (W cm / Sr), λ is the wavelength (μm), λ1 and λ2 are the cutoff wavelengths of the infrared thermal imaging device imaging spectrum (μm), and 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 the absolute temperature (K).

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

[0055] G(T)=aτL(T)+b

[0056] Among them, G is the response grayscale, a and b are fitting coefficients, L is the spectral radiation brightness, τ is the average infrared spectrum transmittance, and T is the absolute temperature.

[0057] In this embodiment, for the all-pass plane mirror, the channel through which light passes through the all-pass plane mirror is set as channel 1, and the grayscale response lower limit G is used by using the curve G(T)=aτ1L(T)+b. k1 and upper limit G k2 The corresponding temperatures are the lower limit temperature T of channel 1. 11 and upper limit temperature T 12 Among them, the two numbers after T, the first one represents the channel number, and the second one represents the upper and lower temperature limits.

[0058] After obtaining the lower limit temperature T of channel 1 11 and upper limit temperature T 12After that, calculate the transmittance, upper limit temperature and lower limit temperature of the attenuation plane mirror. The channel number of the first attenuation plane mirror is designed to be 2. If there are additional attenuation plane mirrors, the channel numbers of the additional attenuation plane mirrors will be the same. Let T 21 =T 12 , we can determine the average transmittance τ2 of the attenuator in channel 2, and the number after the transmittance symbol τ is the channel number. Specifically, using the formula

[0059]

[0060] Obtain the transmittance τ2.

[0061] Then use the formula

[0062] G k1 =aτ2L(T 22 )+b

[0063] Then the upper limit temperature T can be calculated in reverse 22 .

[0064] Repeat the above steps to get the lower limit temperature T of 3 to N channels. i1 and upper limit temperature T i2 , and the average transmittance of the attenuator τ i (i=3…N). Finally, the maximum temperature T that needs to be measured is ensured max Meet the requirements T N1 <T max <T N2 , then repeat the steps and end, determine the number of filter wheel channels N, N-1 is the number of attenuation plane mirrors.

[0065] In some embodiments of the present invention, the total grayscale of the response is determined by:

[0066] Adjust different black body temperatures to obtain the grayscale response of the digital image of the infrared thermal imaging device;

[0067] Determine the total grayscale response of the digital image based on the number of bits of the digital image.

[0068] Specifically, a fixed integration time is determined, and then the infrared thermal imaging device is placed directly against a black body, and different black body temperatures are adjusted to obtain the grayscale response of a digital image of the infrared thermal imaging device.

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

[0070] In some embodiments of the present invention, it further includes:

[0071] The lower limit and upper limit of the response grayscale are determined according to the total grayscale response and the linearity of the radiant brightness.

[0072] The lower limit ratio k1 and upper limit ratio k2 of the grayscale response can be selected according to the current linearity of the selected detector. For the grayscale response and brightness linearity in the full dynamic response range, k1 can be selected from 10% to 20% and k2 can be selected from 80% to 90%. For the grayscale response and brightness linearity in the full dynamic response range, k1 and k2 can be selected from the range with better linear response.

[0073] like Figure 1 As shown, an embodiment of the present invention further provides an infrared testing device for a wide temperature measurement range, which is designed according to any of the above methods, and the device includes 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. The rotating filter wheel is sequentially provided with an all-pass plane mirror and at least one attenuation plane mirror along the circumferential direction. The number of the attenuation plane mirrors and their respective average infrared spectral transmittances are determined by any of the above methods. The rotating filter wheel is used to rotate so that the light spot output by the front-end optical system passes through different all-pass plane mirrors or attenuation plane mirrors to achieve temperature measurement in different temperature ranges.

[0075] In some embodiments of the present invention, the position of each plane mirror of the rotating filter wheel ensures that the light-transmitting surface of each plane mirror on the filter wheel can completely pass the passing light spot without blocking people and light passing through the field of view. When each plane mirror of the filter wheel is switched, both the target and the scene are clearly imaged in the optical path system; wherein the plane mirrors include all-pass plane mirrors and attenuation plane mirrors.

[0076] In some embodiments of the present invention, the thickness of all the plane mirrors is the same.

[0077] In some embodiments of the present invention, when the filter wheel is switched to a different plane mirror, the integration time remains unchanged.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for an infrared thermal imaging device with a wide temperature measurement range, characterized in that: include: An all-pass plane mirror with an average infrared spectrum transmittance of 1 is arranged between the front optical system and the rear infrared detector; A linear relationship between the average infrared spectrum transmittance, the radiation temperature and the total grayscale response is established; wherein the total grayscale response range includes a lower grayscale response limit and an upper grayscale response limit; Determine the lower limit temperature corresponding to the lower limit of the grayscale response of the all-pass plane mirror and the upper limit temperature corresponding to the upper limit of the grayscale response according to the linear relationship; At least one attenuation plane mirror for infrared spectrum is designed between the front optical system and the rear infrared detector; Taking the upper limit temperature corresponding to the all-pass plane mirror as the 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; Every time the lower limit temperature and upper limit temperature corresponding to an attenuation plane mirror are obtained, the following is performed: determining whether the maximum temperature to be measured is between the lower limit temperature and the upper limit temperature corresponding to the attenuation plane mirror; if not, adding an attenuation plane mirror, using the upper limit temperature corresponding to the attenuation plane mirror as the lower limit temperature corresponding to the newly added attenuation plane mirror, calculating 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 according to the linear relationship; if so, stopping adding the attenuation plane mirror.

2. The method according to claim 1, characterized in that The method of establishing a linear relationship between the average infrared spectrum transmittance, the radiant brightness and the response grayscale range includes: Use Planck's formula to establish the radiation brightness formula between black body temperature and black body radiation brightness; The range of the total grayscale of the radiation measurement and the thermal imager response is obtained, and linear fitting is performed to obtain the linear relationship.

3. The method according to claim 2, characterized in that The radiance formula is as follows: Wherein, L is the spectral radiation brightness, λ is the wavelength, λ1 and λ2 are the cut-off 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 Among them, G is the response grayscale, a and b are fitting coefficients, L is the spectral radiation brightness, τ is the average infrared spectrum 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 as follows: Adjust different black body temperatures to obtain the grayscale response of the digital image of the infrared thermal imaging device; Determine the total grayscale response of the digital image based on the number of bits of the digital image.

6. The method according to claim 1, characterized in that Also includes: The lower limit and upper limit of the response grayscale are determined according to the total grayscale response and the linearity of the radiant brightness.

7. An infrared testing device for a wide temperature measurement range, characterized in that: Designed according to any one of the methods in claims 1-6, the device comprises a front-end optical system, a rear-end infrared detector and a rotating filter wheel; The rotating filter wheel is arranged between the front-end optical system and the rear-end infrared detector. The rotating filter wheel is sequentially provided with an all-pass plane mirror and at least one attenuation plane mirror along the circumferential direction. The number of the attenuation plane mirrors and their respective average infrared spectral transmittances are determined by any method 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 all-pass plane mirrors or attenuation 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 of the rotating filter wheel ensures that the light-transmitting surface of each plane mirror on the filter wheel can completely pass the light spot passing through, and does not block the light passing through people and the field of view. When each plane mirror of the filter wheel is switched, the target and the scene are clearly imaged in the optical path system; wherein the plane mirror includes a full-pass plane mirror and an attenuation plane mirror.

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

10. The infrared testing device according to claim 8, characterized in that: When the filter wheel is switched to a different plane mirror, the integration time remains unchanged.

Images