JP2008045891A - Radiation thermometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly-accurate radiation thermometer having a reduced area effect. <P>SOLUTION: This radiation thermometer 1 for measuring a temperature from an infrared ray quantity having an objective lens 6 for condensing infrared rays emitted from a measuring object has characteristics wherein the objective lens 1 is constituted of three lenses, namely, bonded type doublet lenses 6A and a single lens 6B, and the interval (dmm) between the doublet lenses 6A and the single lens 6B and an optical focal distance (fmm) of the objective lens 6 satisfy two relational expressions simultaneously: 80≤f≤100mm (relation 1), and 0.7≤d/f≤0.75 (relation 2). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation thermometer that measures the temperature of an object to be measured by infrared rays emitted from the object to be measured, and more particularly to a standard monochromatic radiation thermometer that performs temperature calibration of the radiation thermometer.

  Conventionally, the movement of heat (heat radiation) as an electromagnetic wave from an object to be measured to a temperature sensor is performed, and a radiation thermometer is used as a thermometer to obtain the temperature of the measurement object by capturing the change in state of the electromagnetic wave. Are known. For calibration using a standard radiation thermometer which is a standard system of this type of radiation thermometer, zinc (419.527 ° C.), aluminum (660.323 ° C.), silver (961.78 ° C.), copper ( A fixed-point black body utilizing the freezing point of a fixed-point substance of 1084.62 ° C. is employed.

As described below, the standard radiation thermometer is defined by JIS (Japanese Industrial Standards) (title General Rules for Performance Test Methods for Radiation Thermometers JIS C 1612: 2000, hereinafter “JIS C 1612”). Two types of monochromatic radiation thermometers are used: 0.9 μm type and 0.65 μm type.
0.9 μm type: A monochromatic radiation thermometer whose center wavelength in the measurement wavelength band is in the range of 0.85 μm to 0.95 μm, and the spectral sensitivity in the wavelength region separated by 0.1 μm or more from the center wavelength is 2 at the center wavelength. × 10 ^-4 or less.
0.65 μm type: Monochromatic radiation thermometer with a center wavelength of 0.64 μm to 0.66 μm in the measurement wavelength band, and the spectral sensitivity in the wavelength region 0.1 μm or more away from the center wavelength is 1 at the center wavelength. × 10 ^-4 or less.

FIG. 10 is a schematic explanatory diagram of a standard monochromatic radiation thermometer described in “JIS C 1612” which is a non-patent document. The standard radiation thermometer 51 is focused on an object to be measured (not shown) through an eyepiece 52, a neutral density filter 53, a relay lens 54, a polarizing mirror 55, an aperture mirror (field stop) 58, and an objective lens 56. Match.
On the other hand, the light (electromagnetic wave) having the measurement wavelength emitted from the object is collected on the objective lens 56 and arranged on the aperture mirror 58 through the aperture stop 57. The aperture mirror 58 has a small hole 58a that limits the field of view, and only the light that has passed through the hole 58a passes through the condenser lens 59 and the interference filter 60 and is guided to the silicon detection element 61.

  Further, as shown in FIG. 11, in order to correct chromatic aberration (aberration caused by a difference in light wavelength) from the visible region to the near infrared region, the objective lens 56 is made of a low dispersion high refractive index glass 56Aa and a high dispersion low refraction. It is composed of a doublet lens 56A and a single lens 56B, which are junction type doublets in which the inner surfaces of the rate glass 56Ab are bonded to each other.

  Furthermore, in the case of a radiation thermometer, an aperture stop 57 is provided so that the indicated value (output value) does not change even if the measurement distance changes, and the lens viewing angle θ can be set even if the objective lens moves back and forth by the focusing operation. It is constant.

And the following performance is calculated | required by the objective-lens optical system used for this kind of radiation thermometer.
1. A bright optical system with a large lens aperture angle to obtain output sensitivity at low temperatures.
2. Focusing is possible according to the measurement distance, and in order to observe the general opening diameter of φ6 mm of the fixed-point blackbody furnace, the minimum condensing area size (hereinafter referred to as the minimum target size) is φ3 mm or less. To do. In the case of a 0.65 μm monochromatic radiation thermometer, the minimum target size shall be 1 mm or less.
3. An optical system with small chromatic aberration in the visible region and the near-infrared region to be measured in order to focus with the direct viewfinder.
4). An optical system with little area effect for high-precision measurement.

  In order to satisfy the requirement 1 regarding the above-described performance, the objective lens of the standard monochromatic radiation thermometer generally has a focal length of 80 to 100 mm and a lens aperture diameter of approximately φ40 mm. Therefore, for example, in a 0.9 μm standard monochromatic radiation thermometer, in order to obtain a measurement sensitivity of about 0.1 ° C. at a minimum temperature of 400 ° C. in the measurement temperature range, a lens aperture diameter of about 40 mm is necessary.

  Furthermore, as a general technique for correcting chromatic aberration (aberration caused by the difference in light wavelength) to satisfy performance requirement 3, two elements of a low dispersion high refractive index glass and a high dispersion low refractive index glass are pasted. It is widely known to use a doublet lens that is a combined compound lens (there is an air-separated tablet with an air gap between the elements and a bonded doublet in which both are bonded on the inner surface). This technology is also applied to measuring objective lenses. With this doublet lens configuration, chromatic aberration correction from the visible range to the near infrared range (550 to 1000 nm) is possible.

  In addition, the area effect in the performance requirement 4 is a phenomenon in which the indication value of the radiation thermometer fluctuates depending on the size of the heat source as a measurement object even when the temperature is the same. The larger the value, the higher the indicated value. According to Non-Patent Document 1, it is considered that the area effect is caused by diffraction by an optical system aperture stop, scattering by an objective lens, reflection in a lens barrel, or the like.

In general, when calibrating the scale of another radiation thermometer with a standard monochromatic radiation thermometer, it is usually performed using a comparative blackbody furnace, although the fixed-point blackbody furnace has an opening diameter of generally 6 mm. On the other hand, the opening diameter of the comparative blackbody furnace is 30 mm to 50 mm. Therefore, when the standard monochromatic radiation thermometer calibrated in the fixed-point blackbody furnace measures a comparative blackbody furnace having a large opening diameter, an error occurs due to the area effect, and accurate scale calibration cannot be performed. This is why a monochromatic radiation thermometer with a small area effect is desired.
JIS C 1612: 2000 Radiation thermometer performance test general rules

  As described above, the error factors that the optical system of the radiation thermometer exerts on the measurement accuracy include insufficient brightness of the optical system, mismatch between the actual measurement target and the optical spot (target), the effects of various optical aberrations and chromatic aberrations, or There is an area effect in which the output of the radiation thermometer changes depending on the difference in the area of the measurement object, and a high-precision measurement performance is required for a radiation thermometer that can measure the temperature of the object in a non-contact manner.

  In addition, objective lenses used in conventional standard monochromatic radiation thermometers mainly focus on ensuring brightness and correcting chromatic aberration, so much attention has been paid to reducing the area effect. I did not come. This is because the area effect factor is complicated and unclear, but the standard monochromatic radiation thermometer is used for calibration of general radiation thermometers. It is a thermometer that requires special minimization of the error factor by the system.

  Further, as shown in FIG. 12 or FIG. 13, the conventional radiation thermometer is arranged with the interval between the objective lenses 56 formed by the doublet lens 56 </ b> A and the single lens 56 </ b> B being narrowed. Compared to when the lens is focused at infinity, the position corresponding to the shorter side shown in FIG. 13, that is, as the lens is moved forward, the light beam diameter (effective diameter) of the first surface increases, resulting in brightness. Is limited. In addition, at the lens position adjusted to infinity, only the light beam passing through a limited portion at the center of the lens is collected, and the other light beam at the outer periphery may become a stray light component in the lens barrel.

  In view of the above, the object of the present invention is to correct brightness and imaging performance by correcting chromatic aberration and spherical aberration from the visible range to the near infrared range (550 to 1000 nm) in the objective lens of the radiation thermometer. In addition, by controlling the traveling direction of the secondary reflected light on the lens surface, an object is to achieve a highly accurate radiation thermometer in which the influence of the area effect is reduced.

In order to solve the above problems, a radiation thermometer according to claim 1 of the present invention is a radiation thermometer that includes an objective lens that collects infrared rays emitted from a measurement object and performs temperature measurement from the amount of infrared rays. The objective lens is composed of a total of three lenses including a cemented doublet lens and a single lens. The distance between the doublet lens and the single lens (dmm) and the optical system focal length (fmm) of the objective lens are as follows. These two relational expressions hold together.
80mm ≦ f ≦ 100mm (Relational formula 1)
0.7 ≦ d / f ≦ 0.75 (Relational formula 2)

  According to a second aspect of the present invention, in the radiation thermometer according to the first aspect, a ghost image position of a reflected light beam between each surface of each lens constituting the objective lens is a normal imaging position by a refracted light beam of each lens. The radius of curvature of each surface of each lens is determined so that the distance from the position of the field stop disposed at a predetermined distance or more or the reflected light beam becomes a diverging light beam.

  According to a third aspect of the present invention, in the radiation thermometer according to the first or second aspect, in each lens constituting the objective lens, the refractive index (nd) and Abbe number (νd) of the glass type are the doublet lens. Nd = 1.65 ± 0.3, νd = 55 ± 5, nd = 1.80 ± 0.5, and νd = 25 ± 5, and the single lens is nd. = 1.65 ± 0.3, νd = 55 ± 5 optical glass, and the image side lens surface has a radius of curvature (R) of 200 mm ≦ R <400 mm (one side is convex and the other side is concave) Lens).

  The invention described in claim 4 is the radiation thermometer according to any one of claims 1 to 3, wherein a standard monochromatic radiation thermometer is used for calibration of the radiation thermometer using a comparative black body furnace. It is characterized by.

  With the above configuration, according to the present invention, the distance between the doublet lens and the single lens is made relatively large, so that the reflected light on the lens surface is allowed to escape to the lens barrel side wall, and unnecessary light rays and light on the outer periphery of the lens. The area effect is reduced by preventing light from a light source far away from the axis center from directly entering the lens.

  Further, by increasing the distance between the doublet lens and the single lens, it is possible to ensure the maximum lens brightness with a certain effective lens diameter.

  In addition, the reflected light beam between each surface of the objective lens is simulated in order, and the ghost image position is more than a predetermined distance from the position of the field stop, which is the normal imaging position by the refracted light beam of the lens, or the divergent light state By defining the radius of curvature of each lens surface, the area effect can be further reduced.

  Hereinafter, the best mode of the present invention will be described with reference to FIGS. FIG. 1 is a layout diagram of an optical system of a radiation thermometer according to the present invention, FIG. 2 is a graph showing the relationship between the inter-lens distance d and the F number, and FIG. 3 is an optical diagram of the radiation thermometer according to the present invention. 4 is an optical path diagram at an infinite focus position of the system, FIG. 4 is an optical path diagram at a short distance focus position of the optical system of the radiation thermometer according to the present invention, and FIG. 5 is an objective lens of the radiation thermometer according to the present invention. FIGS. 6A to 6C are simulation diagrams for tracking various light rays with the fourth surface and the third surface in FIG. 5 as reflection surfaces, and FIG. 7 (a) to (c) are simulation diagrams in the case where various rays are traced using the fifth surface and the first surface in FIG. 5 as reflection surfaces, and FIGS. 8 (a) to (c) are field stops in FIG. It is a simulation diagram when condensing near. Is a graph showing a comparative example of area effect measurement results of the radiation thermometer and a conventional radiation thermometer of the present invention.

  First, the configuration of the radiation thermometer of this example will be specifically described with reference to FIGS. The radiation thermometer described below is a radiation thermometer in which the maximum aperture of the objective lens to be configured is fixed to φ40 mm, and the description of the configuration of the finder optical system such as an eyepiece is omitted.

  As shown in FIG. 1, the radiation thermometer 1 of this example includes a doublet lens 6A and a single lens, which are bonded doublets in which inner surfaces of a low dispersion high refractive index glass 6Aa and a high dispersion low refractive index glass 6Ab are bonded to each other. The infrared rays emitted from the measurement target (not shown) are collected by the objective lens 6 composed of 6B, and the condensed infrared rays are collected on the field stop 8 via the aperture stop 7 and then the condenser lens 9 And reaches the silicon detecting element 11 through the interference filter 10 and is converted into an electrical signal corresponding to the amount of the collected infrared rays.

  More specifically, in the objective lens 6 having a triplet structure of a doublet lens 6A and a single lens 6B composed of a low dispersion high refractive index glass 6Aa and a high dispersion low refractive index glass 6Ab, the maximum aperture diameter of the lens is fixed to 40 mm. In this case, the focal length f of the optical system capable of focusing from a distance of 400 mm to infinity and the distance d in the optical system and the minimum feasible F number (the aperture value, which is expressed as the lens brightness in terms of aperture ratio, is 1 Since this is a smaller numerical value, the reciprocal of the aperture ratio, that is, the numerical value obtained by dividing the focal length by the effective aperture at each aperture is used, so the brightness of the lens is inversely proportional to the square of the F number. As shown in FIG. 2, when d = 72 mm, the F-number has a minimum value of 3, and when the focal length is f = 88 mm, similarly, F = 88 mm. Taking the bar minimum 2.6, if the focal length of f = 80 mm are likewise d = 56 mm, taking the F-number minimum value 2.4. When the objective lens 6 satisfies the relationship of 0.7 ≦ d / f ≦ 0.75 at 80 mm ≦ f ≦ 100 mm between the distance d between the doublet lens 6A and the single lens 6B and the lens focal length f, the F-number is obtained. Minimal and bright lens.

  Further, since the objective lens 6 reduces the area effect due to the stray light component, the ghost image position of the reflected light beam between each surface is a predetermined distance or more from the position of the field stop 8 which is the normal image formation position by the refracted light beam of the lens. The radius of curvature of each surface of the lens is determined so that the reflected light beam is in a divergent light beam state.

  Furthermore, in order to reduce chromatic aberration, the objective lens 6 is a numerical value indicating the refractive index of each lens (nd: the refractive index of the Fraunhofer line with respect to the d-line (587 nm)) and the Abbe number (νd: the dispersion rate of the optical glass, Defined as νd = (nd-1) / (nF-nC), where the refractive indices of the Fraunhofer lines for C-line, D-line, d-line, and F-line are nC, nD, nd, and nF. The two optical glasses having optical characteristics of nd = 1.65 ± 0.3, νd = 55 ± 5, nd = 1.80 ± 0.5, and νd = 25 ± 5. And a single lens 6B which is an optical glass having optical characteristics of nd = 1.65 ± 0.3 and νd = 55 ± 5. In order to reduce the area effect, the radius of curvature (R) of the image side lens surface of the single lens 6B is a meniscus shape of 200 mm ≦ R <400 mm.

  Thus, by providing the objective lens 6 that satisfies the above relationship, the F-number is minimized at an aperture diameter of φ40 mm, resulting in a bright optical system. In addition, the optical system always collects light passing through almost the entire surface of the lens regardless of the focus position of the lens, thereby preventing the incidence of extra light that can be stray light that causes the area effect.

  Further, as shown in FIG. 3 or FIG. 4, since the distance d of the objective lens 6 is set larger than that of the optical system of the conventional radiation thermometer, the position of the principal point moves into the lens system. Even if the lens is moved by focusing, the degree of increase in the effective diameter of the first lens surface becomes small, and it is possible to make it almost the same as the effective diameter in the case of the position at infinity.

  Next, in order to investigate the performance of the radiation thermometer 1 of this example with respect to the area effect, a simulation experiment was performed on the influence of reflected light on each lens surface with reference to FIGS.

  As shown in FIG. 5, in this experiment, the lens surfaces of the objective lens 6 are the first surface, the second surface,..., The fifth surface from the object side in the left direction in the drawing, respectively. Surface 7 was the object surface at a position 500 mm to the left from the first surface. A field stop 8 was placed on the image plane. Then, two arbitrary surfaces are selected from the lens surfaces in the three-lens objective lens 6, and these surfaces are made to act as reflecting surfaces when incident for the first time and as refracting surfaces when incident for the second time. Then, the traveling direction of the light ray was tracked and calculated, and the degree of the light ray passing through the field stop was examined. In this experiment, the number of light rays incident on the first lens surface from the object is 3968, the light rays that have reached the next lens surface are continuously tracked, and the light rays that are outside the lens surface are stopped from being calculated. The number of rays finally passing through the field stop was determined.

  As a specific example, FIG. 6 shows an optical path diagram in the case where the fourth surface and the third surface are reflection surfaces, and light rays having incident angles of 0 °, 7 °, and 10 ° are simulated and traced. 6A is an optical path diagram at an incident angle of 0 °, FIG. 6B is an optical path diagram at an incident angle of 7 °, and FIG. 6C is an optical path diagram at an incident angle of 10 °. In FIGS. 6A to 6C, it can be seen that the reflected light deviates outside the optical system by separating the doublet lens 6A and the single lens 6B from each other.

  Further, the optical path diagram of FIG. 7 is obtained by simulating and tracking the same kind of light rays as in FIG. 6 with the fifth surface and the first surface as reflection surfaces, and FIG. 7A shows the optical path diagram at an incident angle of 0 °. 7B is an optical path diagram at an incident angle of 7 °, and FIG. 7C is an optical path diagram at an incident angle of 10 °. 7A to 7C, it can be seen that a light beam having an incident angle deviates outside the optical system.

  On the other hand, even if the objective lens 6 has the same configuration as that shown in FIG. 7, depending on the radius of curvature of the lens, a ghost image is formed near the field stop 8 as shown in FIGS. In some cases, the amount of reflected light passing through the diaphragm 8 increases. However, in that case, the amount of reflected light passing through the field stop 8 can be reduced by adjusting the entire optical system after changing the radius of curvature of the fifth surface, which is the final lens surface.

  As described above, from the simulation result described above, the ghost image position of the reflected light beam between the surfaces of the objective lens 6 is more than a predetermined distance from the position of the field stop 8 which is the normal imaging position by the refracted light beam of the lens. Alternatively, the area effect can be reduced by determining the radius of curvature of each lens surface so that the reflected light beam is in a divergent light beam state.

Hereinafter, the radiation thermometer 1 of this example will be described more specifically with reference to examples. It should be noted that the following examples are not intended to limit the present invention, and any design changes that fall within the spirit of the preceding and following descriptions are within the technical scope of the present invention.
(Example 1)
As the implementation conditions, the focal length f = 88 mm, F number 2.6, wavelength 0.9 μm, surface number: S, radius of curvature: R (mm) in each lens, surface distance to the next surface: L (mm) The refractive index: n is as shown in Table 1. Further, the glass cord 651562 (S-LAL54) is used as the glass type of the first surface and the fourth surface, and the glass cord 805254 (S-TIH6) is used as the glass material of the second surface.

  FIG. 9 is an example of area effect measurement of a monochromatic radiation thermometer equipped with the objective lens 6 configured in Example 1 and a monochromatic radiation thermometer using a conventional objective lens. As shown in FIG. 9, it can be seen that the radiation thermometer 1 according to the present invention has an area effect reduced to about ¼ compared to the conventional type.

  As described above, the radiation thermometer 1 according to the present invention includes 80 mm ≦ f ≦ 100 mm and 0.7 ≦ d / f ≦ 0.75 between the distance d between the doublet lens 6A and the single lens 6B and the lens focal length f. Since the objective lens 6 satisfying the above relationship is included, chromatic aberration and spherical aberration are corrected from the visible region to the near infrared region (550 to 1000 nm), and brightness and imaging performance are ensured, resulting in the area effect. There is a high-precision that reduces the influence of the area effect by preventing the entry of extra stray light components that are not directly related to the measurement into the optical system and controlling the traveling direction of the reflected light on the lens surface. The radiation thermometer 1 is achieved.

  In addition, the ghost image position of the reflected light beam between each surface of the objective lens 6 is more than a predetermined distance from the position of the field stop 8 which is a normal imaging position by the refracted light beam of the lens, or the reflected light beam is in a divergent light beam state. Thus, by defining the radius of curvature of each surface of the lens, the effect of reducing the area effect is achieved.

  As mentioned above, although the best form in this invention was demonstrated, this invention is not limited with the description and drawing by this form. That is, it is a matter of course that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

It is a layout figure of the optical system of the radiation thermometer which concerns on this invention. It is a graph which shows the relationship between the distance d between lenses, and F number. It is an optical path figure in the infinity focus position of the optical system of the radiation thermometer which concerns on this invention. It is an optical path figure in the short distance focus position of the optical system of the radiation thermometer which concerns on this invention. It is explanatory drawing for demonstrating each lens surface in the objective lens of the radiation thermometer which concerns on this invention. It is a simulation figure at the time of tracking various light rays by making the 4th surface and the 3rd surface in FIG. 5 into a reflective surface. It is a simulation figure at the time of tracking various light rays by making the 5th surface and 1st surface in FIG. 5 into a reflective surface. It is a simulation figure at the time of condensing near a field stop in FIG. It is a graph which shows the comparative example of the area effect measurement result of the radiation thermometer of this invention, and the conventional radiation thermometer. It is a schematic explanatory drawing of the conventional standard monochromatic radiation thermometer. It is a layout figure of the optical system of the conventional radiation thermometer. It is an optical path diagram in the infinity focus position of the conventional optical system. It is an optical path figure in the short distance focus position of the conventional optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation thermometer 2 Eyepiece lens 3 Neutral filter 4 Relay lens 5 Deflection mirror 6 Objective lens 6A Doublet lens 6Aa Low dispersion high refractive index glass 6Ab High dispersion low refractive index glass 6B Single lens 7 Aperture stop 8 Field stop (aperture mirror)
9 Condenser lens 10 Interference filter 11 Silicon detection element

Claims (4)

In a radiation thermometer that has an objective lens for condensing infrared rays emitted from a measurement object and performs temperature measurement from the amount of infrared rays,
The objective lens is composed of a total of three lenses, a cemented tablet lens and a single lens. The distance between the tablet lens and the single lens (dmm) and the optical system focal length (fmm) of the objective lens are as follows. Radiation thermometer with which two relational expressions hold.
80mm ≦ f ≦ 100mm (Relational formula 1)
0.7 ≦ d / f ≦ 0.75 (Relational formula 2) The ghost image position of the reflected light beam between each surface of each lens constituting the objective lens is more than a predetermined distance from the position of the field stop arranged at the normal coupling position by the refracted light beam of each lens, or the reflection The radiation thermometer according to claim 1, wherein a radius of curvature of each surface of each lens is determined so that the light beam becomes a divergent light beam. In each lens constituting the objective lens, the refractive index (nd) and Abbe number (νd) of the glass type are nd = 1.65 ± 0.3, νd = 55 ± 5 and nd = 1. Two optical glasses having 80 ± 0.5 and νd = 25 ± 5 are bonded together, and the single lens is an optical glass having nd = 1.65 ± 0.3 and νd = 55 ± 5, and an image. 3. A radiation thermometer according to claim 1, wherein the side lens surface has a meniscus shape with a radius of curvature of 200 mm ≦ R <400 mm. The monochromatic radiation thermometer for standards according to any one of claims 1 to 3, which is used for calibration of a radiation thermometer using a comparative black body furnace.

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