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    • 专利摘要:
    Device and optical measurement system of the reflection coefficient of a surface. The present invention relates to a novel device for optical measurement of the reflection coefficient of a surface (1), comprising: one or more optical channels, wherein each channel comprises a plurality of leds (2) for the emission of a beam of illumination in one or more wavelengths; a first photodetector (4) for measuring the direct illumination beam of the leds in the optical channel; a diaphragm (5) located at the exit of the optical illumination channel, to limit the exit opening of the illumination beam; a lens (6) arranged to receive the beam reflected on the surface (1) and to focus said beam; and a second photodetector (8) for measuring the signal of the illumination beam reflected by the surface (1) to be measured. The device of the invention is capable of minimizing the amount of diffuse light present in the measurement without losing a high intrinsic tolerance of the measure against different curvatures and different thicknesses of mirrors, without needing to make any additional adjustment in said device. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2603650A1
    申请号:ES201531138
    申请日:2015-07-30
    公开日:2017-02-28
    发明作者:Noelia Martínez Sanz；Carlos Alcañiz García；David Izquierdo Núñez；Carlos Heras Vila；Íñigo SALINAS ARIZ；Cristina Pelayo Gil；Rafael Alonso Esteban；Victor ZARZA ESCOBAR
    申请人:Abengoa Solar New Technologies SA；
    IPC主号:
    专利说明:

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    DESCRIPTION
    DEVICE AND OPTICAL MEASUREMENT SYSTEM OF THE COEFFICIENT OF REFLECTION OF A SURFACE
    FIELD OF THE INVENTION
    The present invention is part of the field of optical technologies for measuring the reflection or reflectance coefficient. More specifically, the invention relates to a device for measuring the coefficient of reflection on surfaces and to a system comprising said device. The invention is of preferential application in the measurement of the reflection coefficient of solar concentrator surfaces, as well as in other reflective elements used in solar energy capture technologies.
    BACKGROUND OF THE INVENTION
    Within the renewable energy sector, thermal solar energy collection currently has great technological and economic importance, both in the domestic and industrial fields. Among the ways of obtaining thermal solar energy, thermoelectric solar energy produces electricity with a conventional thermoelectric cycle, which requires the heating of a fluid at high temperature, usually through the concentration of solar radiation by means of reflective elements. In solar thermal power plants, the measurement of the value of the reflection coefficient of these elements plays a very important role in knowing the performance of solar thermal power plants, as well as in optimizing their efficiency.
    For the operation and maintenance of electrical energy production facilities, due to the large number of mirrors included in them, it is convenient to have equipment that allows the characterization of the reflection coefficient of each mirror to be carried out quickly, comfortably and easily. Equipment that performs such a measurement is called reflectometers.
    Given the optical characteristics of the solar energy absorbing elements included in these solar plants (where maximum energy absorption and minimum energy losses are required, which determines parameter dependencies
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    optical with the wavelength), the equipment must provide measurements of the reflection coefficient of the mirrors as a function of the wavelength. Likewise, the equipment must provide with precision the measurement of extreme reflection values, close to the unit, generally in unfavorable environmental conditions since the ambient light is usually of high intensity.
    On the other hand, the reflection in the mirrors can be of two types: diffuse and specular. The diffuse reflection is omnidirectional, unlike the specular reflection, in which the beam is reflected in a reflection angle equal to the angle of incidence. Due to the dirt that is deposited on the surface of the mirrors in the plant, the reflection of sunlight will have diffuse and specular components, the specular reflection being only useful from the point of view of energy generation, since it is the only one that It will concentrate on the absorber element. Therefore, the team must minimize the contribution of diffuse reflection on the measurement of the reflection coefficient of the mirrors.
    On the other hand, the equipment must have the ability to correctly measure the set of types of mirrors commonly used in the plants. Specifically, they should be able to correctly measure flat and parabolic-parabolic mirrors of different thicknesses, without the need for additional adjustments. For this, each team must have an optical design in which it is ensured that, for the set of mirrors to be measured, the entire beam of light reflected specularly by the mirror is always collected in detection. That is, to ensure a precise measurement, the equipment must have tolerance with respect to the distance to which the reflective surface is and its geometry.
    Within the set of portable spectrophotometers, those that use light emitting diodes (LEDs) as light sources at different wavelengths stand out. In US patent 2008/0144004 several LEDs are used simultaneously to perform a transmission measurement for the detection of different blood analytes. However, a true spectral measurement is not performed, but several simultaneous measurements in a few different wavelengths. In addition, there is no protection against ambient light nor is it possible to carry out reflection or reference measurements.
    Of special relevance is WO 2011/104401 A1, owned by Abengoa Solar New Technologies. It discloses a spectrophotometer comprising a set of LEDs to perform the spectral measurement, so that each LED forms a
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    optical channel, and thus each LED requires a lens, an LED output diaphragm and two detectors, so the number of components (lens, diaphragms and detectors) grows proportionally with the number of measurement LEDs. In said invention, the optical channels are arranged online or in a circle. Thus, when the arrangement of the optical channels is in line, the size of the equipment increases proportionally with the number of LEDs and, when the arrangement of the optical channels is in a circle, the maximum number of LEDs is limited by the diameter of the circle. the space that each measuring channel occupies. Finally, in the mentioned patent, the amount of diffused light present in the measurement is minimized by limiting the numerical opening of the illumination beam from the LED, so that the area illuminated on the mirror is as small as possible.
    Also of special relevance is patent application ES2533778, owned by Abengoa Solar New Technologies. It claims the invention of a portable device for measuring the transmission of the outer tube and reflection of the inner tube of the receiving tubes for thermosolar plants of parabolic trough cylinder technology (CCP). This equipment uses lighting integrating spheres so that a set of LEDs share a lens, the same reference detector and the same measurement detector, thus reducing the size of the equipment and the number of detectors of the equipment.
    In the patent application ES2533778, the measurement strategy consists in obtaining an extensive and very uniform illumination beam, so that the measurement detector does not collect the entire light beam, but only a small part of this illumination beam .
    Thus, the tolerance of the equipment is based on the uniformity of this illumination beam, but a measurement error will occur due to the divergence of the beam when the distance between the light source and the measurement detector varies. Following this measurement strategy, in this equipment an integrating lighting sphere with several LEDs is used and placing a lens just at the exit of the sphere, before the sample to be measured, with the aim of collimating the beam, forming an image or working with divergent beam. Therefore, diaphragm is not used at the exit of the sphere to limit the opening of the beam.
    Within the measurement systems of the reflection coefficient, the strategies to minimize the contribution of diffused light in the measurements made stand out. In general, in the optical designs of the measurement systems, there is an inversely proportional relationship between the contribution of diffused light in the measurement and the angle of measurement acceptance (the set of angles of incidence of the rays
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    that will reach the detector and therefore will be measured). Thus, greater angles of measurement acceptance also imply greater contribution of diffused light in the measurement, so that the strategy to minimize the amount of diffused light is based on limiting the angle of measurement acceptance. The most common strategy in the measurement of specular reflection is to use circular diaphragms placed in front of the detector, which limit the angle of acceptance a few milliradianes. By limiting the angle of acceptance, the equipment does not have intrinsic tolerance regarding the thicknesses and curvatures of the mirror, so it requires a manual mechanical adjustment prior to the measurement, by means of three external levelers, which entails increasing the times and errors of the measures.
    Although the previous technical proposals allow an approximation, none of the aforementioned or similar equipment simultaneously meet the necessary requirements for the field measurement of mirrors for solar collectors (tolerance with respect to the distance at which the reflective surface is located and its geometry and minimization of the contribution of diffused light), either by range, sensitivity, tolerance, size and / or mechanical configuration. The present invention is presented, then, as a solution to this technical problem, allowing both flat and spherical mirrors to be measured, such as parabolic troughs of different thicknesses, and limiting the contribution of diffused light on the measurements.
    BRIEF DESCRIPTION OF THE INVENTION
    An object of the present invention is, therefore, the obtaining of measuring equipment of optical properties on surfaces of solar collectors that are portable, robust, manageable, with rapid measurement, sensitivity and adequate dynamic range, with sufficient tolerance in curvature and thickness of the mirror to be measured, and that minimize the contribution of diffuse reflection in the measurement.
    Said object is preferably carried out by means of an optical measuring device for the reflection coefficient of a surface, comprising:
    - one or more optical channels, where each channel comprises a plurality of LEDs for the emission of a beam of illumination at one or more wavelengths;
    - a first reference photodetector for measuring the beam of direct illumination of the LEDs in the optical channel;
    - a diaphragm located at the exit of the optical illumination channel, to limit the opening of the illumination beam output;
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    - a lens arranged to receive the beam reflected on the surface and to focus said beam;
    - a second photodetector for measuring the signal of the illumination beam reflected by the surface to be measured, said photodetector being equipped with an effective rectangular detection region, where the shorter side of said rectangular region is arranged perpendicular to the plane of incidence of the surface to be measured (that is, the plane containing the normal to the reflection surface and the optical axis of the channel of the device), and where the side of greater length is arranged parallel to said plane.
    Unlike the optical design disclosed in WO 2011/104401 A1, in the device proposed in the present invention, use is made of lighting integrating spheres, so that a number preferably between two and ten LEDs form a single optical channel, share the same lens, the same output diaphragm and the two detectors, which considerably reduces the size of the device and the number of necessary components.
    Unlike the equipment described in patent application ES2533778, in the device proposed in the present invention the measurement strategy consists in obtaining a very small beam of light on the sample to be measured, so that in the measurement detector all the beam of illumination. Thus, the tolerance of the device is based on the ability to collect the entire beam of illumination with the measurement detector for the different distances of the reflective surface due to thicknesses and curvatures of the mirror. Following this strategy, in the device of the present invention an integrating illumination sphere with several LEDs is used using a diaphragm just at the exit of the sphere to limit the opening of the beam and placing a lens after reflection in the sample, to collect the entire beam reflected in the mirror and focus it on the measurement detector.
    With regard to the angle of acceptance of the radiation incident in the second photodetector, unlike the strategies proposed in the state of the art, a photodetector with an effective region of substantially rectangular detection is used in the device proposed in the present invention. Said effective region should be understood as the "sensitive" surface of the detector that captures and measures, in the device, the reflected solar radiation. So that said sensitive surface preserves its rectangular shape, it is possible to use different technical approaches, such as the use of a rectangular diaphragm placed after the collection lens
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    and focusing and in front of the photodetector. In addition to the side that has the opening of greater length of the diaphragm, it must be placed parallel to the plane of incidence of the beam on the sample and therefore the side that presents the opening of smaller length perpendicular to the plane of incidence of the surface to be measured, thus, the contribution of diffused light is minimized in the plane perpendicular to the plane of incidence, but maintaining the tolerance of the device with respect to thicknesses and curvatures of the mirror. Alternatively, said sensitive detection surface may be the photodetector's own surface, in case this photodetector is previously configured with the required rectangular shape and also oriented with the side of greater length parallel to the plane of incidence of the beam on the sample.
    On the other hand, in a preferred embodiment of the invention, for each optical channel, the LEDs and the first photodetector are housed in an integrating lighting sphere equipped with an exit hole, arranged so that the light emitted by the LEDs can reflected on the inner surface of said sphere, and where a part of that light exits through said exit hole of the sphere. Also, in a preferred embodiment of the invention each optical channel houses at least two LEDs, which are modulated at different frequencies and configured to be able to light individually or simultaneously, in order (in the case of lighting simultaneously) to decrease the time of measurement of the reflection coefficient. More preferably, each optical channel comprises at least one LED with identical wavelength in each channel, and therefore being in different channels, with different spatial positioning. The objective of having said LED, is to compensate, in the measure of the reflection coefficient, the fact that each optical channel can be measuring in two different points of the reflecting surface.
    In another preferred embodiment of the invention, the exit orifice of the integrating sphere is oriented in the optical axis of the device, with a defined angle of incidence on the surface to be measured, so that the vector defining the direction of exit of the beam of light of the sphere forms an angle equal to said angle of incidence with the normal vector to the surface.
    In another preferred embodiment of the invention, the lens has a width at least twice the width of the beam at the position of said lens.
    In another preferred embodiment of the invention, the device comprises a second rectangular diaphragm to limit the acceptance field of the second photodetector of
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    measurement, located adjacent to the lens and aligned with it in the path of the reflected beam. More preferably, the side of greater length of the second diaphragm should be placed parallel to the plane of incidence of the beam on the sample and the one of shorter length will therefore be located perpendicular to the plane of incidence of the surface to be measured.
    In another preferred embodiment of the invention, the device comprises at least two optical channels, where each optical channel is equipped with at least two emission LEDs at different wavelengths.
    As mentioned above, the device measures the mirror reflection coefficient of mirrors at different wavelengths, determined by LEDs. The mirrors object of characterization can be flat or curved, and can be mirrors of first or second face with different thicknesses.
    Each optical measuring channel is formed by a set of, preferably, between two and ten LEDs placed in a lighting integrating sphere, a first reference photodetector placed in the integrating sphere, a diaphragm placed at the exit of the integrating sphere, a lens that collects the beam reflected in the mirror and focuses the beam, a second diaphragm that limits the range of acceptance of the measurement and a second photodetector of the reflected light. For each optical measurement channel of the reflection coefficient, the device performs two measurements, a reference measurement on a percentage of the light emitted by each LED and a direct measurement of the light reflected specularly by the mirror. The device performs simultaneous reference and direct measurement to adequately correct the variations in the emission power of the LED of said channel.
    The LEDs of the device can be turned on individually or simultaneously in order to reduce the measurement time. The LEDs of different channels are distinguished spatially, while the LEDs belonging to the same optical channel can be distinguished by modulating them at different frequencies. That is, two LEDs can be lit at the same time, being either of the same sphere (optical channel) or of different spheres (different optical channels). In that case, the LEDs of different spheres, (different optical channels) differ spatially, that is, they differ because the spheres are located in different positions. The LEDs of the same sphere (same optical channel) that light up at the same time differ because they are modulated at different frequencies.
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    The number of optical channels can be variable, for example from one to four, covering the desired spectral range with commercial LEDs in the near-infrared ultraviolet range. With the usual requirements for the spectral characterization of a solar thermal energy production facility, it may be sufficient to have about two integrating spheres, including six measuring wavelengths each.
    For each optical channel, the angle of incidence of the beam of light coming from the integrating sphere and the angle of collection of the beam of light reflected by the mirror is the same, to ensure the measurement of specular reflection. The tolerance of the measurement with respect to thicknesses and curvatures of the mirrors is determined by the ability of the system to measure all the light reflected specularly by the mirror. To ensure adequate tolerance, the numerical opening of the illumination beam is limited by means of a first diaphragm of certain diameter and length placed at the exit of the integrating sphere and oriented on the optical axis of the system to ensure the angle of incidence of the beam of light required on the mirror.
    The beam reflected by the mirror in specular reflection is collected by a lens, which focuses the beam on a second photodetector for direct measurement of the light reflected specularly by the mirror. This lens and photodetector system are oriented on the optical axis of the system to ensure the angle of collection of the light beam in specular reflection. The size of the lens in relation to the size of the beam at that point determines the tolerance of the system against the curvature of the mirror and against the position of the mirrored surface with respect to the measuring device determined by the thickness of the glass that protects the face mirrored If the size of the lens is not greater than the size of the beam at that point, the conditions of curvature of the mirror or thickness of the mirror for the correct measurement would be unique, and variations thereof would cause that not all of the reflected beam of light Specifically, through the mirror, it was picked up by the lens and reached the photodetector, resulting in an error in the measurement of the reflection coefficient. In order to have sufficient tolerance in curvature and thicknesses of the usual mirrors in a solar thermal energy production facility, a lens size that is twice the size of the beam at that point may be sufficient.
    The fact of working with a lens that is greater than the size of the beam at that point to achieve tolerance of the system against thicknesses and curvatures, propitiates as
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    In contrast, there is an amount of diffused light that is collected by the lens and measured by the photodetector, resulting in errors in the measurement of specular reflectance.
    This amount of diffused light is determined by the acceptance angle of the photodetector, that is, the set of angles of incidence of the rays that will reach the photodetector and will therefore be measured. As commercial photodetectors generally have a sensitive area that is square or circular, to minimize the amount of diffused light measured in the photodetector without losing tolerance in the device, the device includes a diaphragm in front of the rectangular shaped photodetector, so that the side presenting the longest length opening of this diaphragm is oriented in the plane of incidence of the beam to maintain the tolerance of the device, and the side presenting the shortest length opening of this diaphragm is oriented perpendicular to the plane of incidence of the beam to block in this direction the diffused light that would reach the photodetector. The same result could be achieved by working with photodetectors that had a sensitive area of rectangular shape, orienting the long axis of the sensitive area in the plane of incidence, and in this case it would not be necessary to include the diaphragm in front of the detector since the photodetector itself it would limit the diffuse light on the axis perpendicular to the plane of incidence.
    The combination of the optical parameters of numerical aperture of the illumination beam, lens size and lens focus determine the relative positions of the integrating sphere, mirror, lens and photodetector assembly and therefore the size of the device. To achieve a manageable portable device that minimizes the amount of diffused light, focal lenses between 15 mm and 30 mm and maximum diameter of half an inch are desirable.
    Another object of the present invention relates to a system for measuring the reflection properties of a surface, comprising a measuring device according to any of the embodiments described herein, wherein said device is connected to:
    - a circuit configured to perform the functions of analogue / digital acquisition and conversion of the signals detected by the photodetectors;
    - a signal processing circuit configured to process and extract the signal from the background of ambient optical and electrical noise associated with the measurement;
    - A central processing unit internal or external to the device .;
    - A system for storing the data obtained.
    - A system for user interface with the keyboard, screen or other elements.
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    - an insulation housing of the electronic and optical components of the system.
    In a preferred embodiment of the invention, the system comprises software implemented in the central processing unit for the communication of the device with it, and for the treatment of the information acquired by the measuring device.
    In another preferred embodiment of the invention, the system comprises an interface for communicating with the user via keyboard and / or screen.
    In another preferred embodiment of the invention, the system comprises a means of communication with a computer, tablet, or mobile device external to said system.
    To obtain a measurement with high sensitivity, which allows to precisely resolve values of the reflection coefficients very close to the unit, it is necessary that the acquisition system has a sufficiently large signal to noise ratio. Since the optical background signal comes mainly from ambient sunlight, that is, it is a signal of great intensity, it is essential to perform some type of treatment to that signal that allows the signal / noise ratio to be high. The most indicated in this case is the digital signal processing by applying some extraction algorithm such as synchronous detection or lock-in. To perform such a treatment, it is necessary that the signal to be measured can be easily distinguished from the noise background, something that is usually achieved by applying some type of modulation to it.
    Another advantageous feature in such a system is the possibility of exporting data comfortably and flexibly to a personal computer, where they can be treated and stored in the way that is considered most convenient. This can be solved by wireless communication with a conventional network protocol, by connection via conventional USB port or also by incorporating the processing capacity in the device itself and extracting the data through conventional SD memory.
    The general scheme of the measurement system of the invention is as follows:
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    - One or several lighting integrating spheres that each include several light emitting diodes or LEDs, covering the range of wavelengths in which the mirrors wish to be characterized. In a preferred embodiment, one LED would be used for each wavelength. Also in a preferred embodiment the same LED could be repeated in two different spheres to adjust differences in the reflection coefficient when measuring at different points of the mirror.
    - Two photodetectors per lighting integrating sphere used, to obtain the reference and direct signal for each of the wavelengths.
    - A circuit configured to perform the functions of acquisition and analog / digital conversion of the signals of interest.
    - A signal processing circuit configured to process and extract the signal from the possible background of ambient optical and electrical noise. This circuit can also be in charge, if necessary, of applying the modulation chosen to the LED sources.
    - A central processing unit internal or external to the device, which controls the overall operation of the system, selecting the electronic components corresponding to the channel used at all times and governing internal and external communications.
    - A subsystem of interface of the equipment with the user by means of keyboard, screen or other elements.
    - A housing that provides adequate insulation of the electronic and optical components of the system, allows it to be transported easily and easily and repetitively coupled to the mirrors to be measured.
    - Optionally, a means of communication with an external device (computer, tablet, mobile ...).
    - Optionally, a software implemented in the external device for communication with it, and for the treatment of the information acquired by the measuring device.
    One of the advantages and advances provided by the invention is the fact that the system is capable of minimizing the amount of diffused light present in the measurement without losing a high intrinsic tolerance of the measurement against different curvatures and different thicknesses of the mirrors, no need to make any adjustments to the device.
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    Another very important advance is that the system allows a high number of LEDs to be included without increasing the size of the device, which is of great relevance for portable field devices.
    DESCRIPTION OF THE FIGURES
    In order to help a better understanding of the characteristics of the invention, a series of figures accompany this descriptive memory where, with a merely indicative and non-limiting nature, the following has been represented:
    Figure 1 represents a scheme of the optical system corresponding to an optical channel formed by a lighting sphere, which includes several emitters and the first reference photodetector, a first diaphragm at the exit of the sphere, a lens, a second diaphragm and a second photodetector of reflected light measurement, with its spatial arrangement with respect to the mirror to be measured.
    Figure 2 represents the displacement in the plane of incidence suffered by the beam of light reflected in the mirror due to changes in thickness and / or curvature thereof.
    Figure 3 represents the detail of the second diaphragm placed in front of the second photodetector to limit the acceptance angle of the photodetector in the axis perpendicular to the plane of incidence without losing tolerance.
    Figure 4 represents the top view of the mechanical base where the optoelectronic components of the system are included.
    Figure 5 represents the bottom view of the mechanical base where the optoelectronic components of the system are included.
    Figure 6 represents the complete scheme of the proposed embodiment, including the optical system and the electronic components, as well as the data acquisition card that performs the functions of analog / digital conversion of the signals and communication with the PC.
    - Description of the numerical references used in the figures:
    (1) Mirror to characterize ((1 ’) mirrored surface, (1’) mirror glass).
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    (2) LED light beam emitters.
    (3) Integrative lighting sphere.
    (3 ’) Exit hole of the integrating sphere.
    (4) Reflection reference photodetector.
    (5) Diaphragm that limits the size of the beam on the mirror surface.
    (6) Lens that collects the beam reflected by the mirror.
    (7) Rectangular diaphragm that limits the acceptance angle of the photodetector.
    (8) Measurement detector for reflection of the light reflected by the mirror.
    (9) Optical axis of the system.
    (9 ’) Angle of incidence of the output light.
    (9 ’) Plane of incidence of the light beam.
    (10) Displacement of the mirrored surface due to change in thickness and / or curvature.
    (11) Displacement of the light beam reflected in the mirror due to change in thickness and / or curvature.
    (12) Longer side of the diaphragm that limits the angle of acceptance in the detector, placed parallel to the plane of incidence of the light beam.
    (13) Side of smaller diaphragm length that limits the angle of acceptance in the detector, placed perpendicular to the plane of incidence of the light beam.
    (14) Mechanical base support elements.
    (15) Microprocessor or similar.
    (16) Modulation signals.
    (17) Analog electrical signals measured in photodetectors.
    (18) Control signals through digital outputs.
    (19) Sinusoidal LED power supply signal.
    (20) Transimpedance amplifier.
    (21) User interface.
    (22) Data.
    (23) Commands.
    (24) External teams.
    DETAILED DESCRIPTION OF THE INVENTION
    A preferred embodiment is proposed based on an optical device that contemplates for each optical channel the configuration shown in Figure 1 of this document.
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    The reflective surfaces (1) for solar collectors are usually second-sided mirrors, so that on the mirrored surface there is a glass of thickness between approximately 1 mm and 5 mm. These mirrors can be flat, with spherical curvature, or parabolic trough, as in the case of solar concentrating plants on tubes. The mirror must have a very high reflection coefficient in the solar spectrum.
    The reflection measurement is obtained from the measurement made by a photodetector (8) of reflection after the beam generated by each LED emitter (2), crosses the outer glass (1 '') twice and is reflected specularly in the mirrored surface (1 ').
    To share the same optical axis and optical channel, a set of LED diodes (2a - 2f) are placed in an integrating lighting sphere (3) so that the light they emit enters the sphere and after several reflections, a part of that light exits through the exit hole (3 ') of the integrating sphere (3). This exit orifice (3 ') is oriented on the optical axis (9) of the device channel, with an angle of incidence (9') defined on the mirror (1), so that the output direction of the beam of light of the sphere with the orientation in which the mirror surface is located. In this preferred embodiment, the angle of incidence (9 ’) is 12 °. This output beam of the sphere in the direction of the mirror is limited in numerical aperture by a diaphragm (5) to ensure the size of the beam on the mirrored surface. On the other hand, the device obtains a reference signal from the measurement of part of the light inside the sphere (3) by means of the detector (4).
    The specular reflection of the beam in the mirror is collected by the lens (6) twice as large as the beam size at this point. This lens (6) is oriented according to the optical axis of the system, and focuses the light beam on the direct light measurement detector (8). In front of the direct light measurement detector (8) a diaphragm (7) is placed whose opening is rectangular in order to limit the angle of acceptance of the detector in the direction perpendicular to the plane of incidence (9 '') and without limiting the angle of acceptance of the detector in the direction parallel to the plane of incidence (9 ''), so that in this direction it is the size of the effective area of the detector that limits the measured light beams, thus maintaining the tolerance of the measurement with respect to thicknesses and curvatures of the mirrors that produce displacements of the light beam in the detector within the plane of incidence (9 '').
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    Figure 2 shows the displacement of the beam of light reflected in the mirror (1) when it suffers a displacement (10) either by changing thicknesses or by changing curvatures, so that the beam collected by the lens (6) and focused on the detector (8) it suffers a displacement (11) on the surface of the detector (8). These displacements will always occur in the incidence plane (9 ’), a plane that contains the normal to the reflection surface and to the optical axis (9) of the device channel.
    The detail of the diaphragm (7) to limit the acceptance angle of the detector (8) is shown in Figure 3. The opening of this diaphragm is rectangular, so that the side with the longest opening (12) of the rectangle is placed parallel to the plane of incidence (9 ''), so that it does not limit the angle of acceptance of the detector itself (8). In turn, the side that presents the opening of smaller length (13) of the rectangle is placed perpendicular to the plane of incidence (9 ’), so that it limits the angle of acceptance of the detector itself. Thus, the beam from the reflection of the mirror and which can suffer displacements (11) due to different thicknesses or curvatures, reaches the detector in its entirety without being limited by the diaphragm tolerance (7). The figure shows three positions of the beam displaced in the plane of incidence (9 ’). At the same time, diffused light is limited in the plane perpendicular to the plane of incidence (9 ’) due to the shorter opening of the diaphragm (13).
    In this preferred embodiment, the device consists of two optical measurement channels, therefore it consists of two integrating lighting spheres (3). An optical channel incorporates Si photodetectors to cover the range from 300 nm to 1050 nm and includes in the integrating sphere eight LEDs (2) that cover this spectral range. The other optical channel includes InGaAs photodetectors to cover the range from 1050 nm to 2200 nm and includes six LEDs in the sphere that cover this spectral range. Figures 4 and 5 show the mechanical base (14) containing the set of basic elements that form the optical system (shown in Figure 1, and comprising two integrating spheres (3), LEDs (2), two diaphragms of output (5), two lenses (6), two diaphragms (7) that limit the angle of acceptance, two measurement photodetectors (8) and two reference photodetectors (4), one for each integrating sphere (3)). On the upper face of said mechanical base (14) the two spheres (3) are placed with their corresponding LEDs (2) and the reference photodetector (4) inside and the direct light photodetectors (8). The lenses (6) and the outlet diaphragms (5) of the sphere (3) are placed on the lower face which in this embodiment are
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    external parts that are inserted in holes in the mechanical base (14) that connect to the exit of the sphere (3). In front of the photodetector (4) the diaphragm (7) is placed that limits the acceptance of the detector, which has an opening or rectangular shape with the long side placed parallel to the plane of incidence (9 ’) (shown in Figure 3). Rubber gaskets (not shown in the figures) placed along the lower profile of the mechanical base (14) ensure the correct support of the device on the mirror (1) without damaging it.
    Figure 6 shows the complete scheme including the data acquisition and processing system, which in this preferred embodiment is implemented through the use of a microprocessor (15) or DSP, or the like. In this microprocessor (15) the modulation signals (16) are generated, the analog signals (17) generated in the photodetectors (4, 8) are digitized and the filtering thereof is performed by programming a synchronous amplification algorithm (lock-in). Also this microprocessor (15) performs the control by means of digital outputs (18) of the supply of the plates of emitters (2) and photodetectors (4, 8). To ensure that the measurement can be carried out without the influence of ambient light and at the same time measuring several LEDs (2) that share the same optical channel, the data acquisition and processing system consists of a signal from the emitters (19) that are modulates sinusoidally varying the supply current of the LEDs (2) at a specific frequency. The system can generate several modulation frequencies (16) to simultaneously modulate several LEDs (2) of the same sphere with different frequencies each to be able to differentiate them in the detection. This modulation at different frequencies allows to extract the signal of interest in the photodetectors (4, 8), filtering all the frequency components except the one corresponding to each LED (2) that is being modulated at each specific frequency. By being able to modulate and measure several LEDs (2) of the same sphere at the same time, the measurement time is reduced. In this preferred embodiment, the system generates two different modulation frequencies and two LEDs (2) of each sphere (3) are modulated at the same time, so that four LEDs (2) are turned on and measured at the same time.
    In a preferred embodiment, eight LEDs (2) have been chosen for an integrating sphere (3) with wavelengths - 395, 435, 525, 650, 780, 850, 940 and 1050 nm and three LEDs ( 2) for the other integrating sphere (3), with wavelengths of 1050, 1300 and 1550 nm. The two spheres (3) include an LED (2) of 1050 nm to measure at the same wavelength and thus compensate to the extent
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    made of measuring at two different points of the mirror (1) each optical channel.
    In addition, the photodetectors (4, 8) are followed by two amplification stages (20) whose gain depends on the value of the resistors they include. One of these resistors can be a digital potentiometer whose value can be controlled via software, which allows you to adjust the gain of each channel at any time using the outputs of the microprocessor (15).
    The microprocessor (15) communicates with the user interface system (21) through data (22) and control commands (23). This user interface includes screen and keyboard to represent the measurements and select device configurations, and includes communication with external equipment (24) via USB or wireless bluetooth or similar. The system also includes a data storage system not shown in the figures for further processing.
    The method of operation of the device comprises the following steps for obtaining the measurement of the reflection coefficient:
    a) Position the device so that it rests stably on the mirror (1).
    b) In a row, at least two LEDs (2) of each sphere (3) are lit at the same time, each of the LEDs (2) of the same sphere (3) modulated at a different frequency, and the measurement is made of the reflection coefficient in their corresponding wavelengths. The data obtained in the reflection detector (8) corresponding to the LED (2) modulated at a frequency is normalized with its reference measurement at that frequency, to eliminate the influence of the variations in the emission intensity of each LED (2) .
    c) Subsequently, the reflection coefficient of the mirror (1) is obtained for each measurement wavelength. This final value of the coefficient is also obtained by reference to a known pattern.
    d) If desired, the reflection coefficients measured in each sphere are adjusted by software due to the fact of measuring at different points of the mirror (1). For this, the reflection data of the LED (2) of 1050 measured with each sphere (3) is used, calculating the necessary offset so that the measurement of the reflection coefficient of this LED (2) is well adjusted to the maximum value, to the value minimum or at
    average value obtained in the two LEDs. Thus, all the data of one of the spheres (3) (if the maximum or minimum is used) or of the two spheres (3) (if the average is used) are adjusted using the offset that has been calculated for the LED (2) 1050 nm.
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    e) The values corresponding to the pattern are stored in the device after a previous calibration, which requires the use of a mirror (1) with known reflection coefficients. This calibration is performed following the first three steps of this same procedure.
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    Thus, although the main application of this invention is the use of the device for the on-site control of the optical characteristics of flat (parabolic) mirrors (1) of solar thermal power plants, its extension to other fields of industry is not ruled out. that require a measuring device with similar characteristics.
    权利要求:
    Claims (15)
    [1]
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    1. - Optical measuring device for the reflection coefficient of a surface (1), characterized in that it comprises:
    - one or more optical channels, where each channel comprises a plurality of LEDs (2) for the emission of a beam of illumination at one or more wavelengths;
    - a first photodetector (4) for measuring the beam of direct illumination of the LEDs in the optical channel;
    - a diaphragm (5) located at the exit of the optical illumination channel, to limit the opening of the illumination beam output;
    - a lens (6) arranged to receive the beam reflected on the surface (1) and to focus said beam;
    - a second photodetector (8) for measuring the signal of the illumination beam reflected by the surface (1) to be measured, said photodetector being equipped with an effective rectangular detection region, where the shorter side (13) of said rectangular region is arranged perpendicular to the plane of incidence (9 '') that contains the normal to the surface (1) of reflection and the optical axis (9) of the channel of the device, and where the side of greater length (12) is arranged parallel to said plane (9``).
    [2]
    2. - Device according to the previous claim where, for each optical channel, the LEDs (2) and the first photodetector (4) are housed in an integrating lighting sphere (3) equipped with an exit hole (3 '), arranged so that the light emitted by the LEDs (2) can be reflected on the internal surface of said sphere (3), and where a part of that light exits through said exit hole (3 ') of the sphere.
    [3]
    3. - Device according to the preceding claim, wherein the outlet orifice (3 ') of the integrating sphere (3) is oriented on the optical axis of the device, with an angle of incidence (9') defined on the surface to be measured ( 1), so that the vector that defines the direction of exit of the light beam of the sphere (3) forms with the normal vector to the surface an angle equal to said angle of incidence (9 ').
    [4]
    4. - Device according to any of the preceding claims, wherein each optical channel comprises at least two LEDs modulated at different frequencies and configured to be able to light individually or simultaneously.
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    [5]
    5. - Device according to the preceding claim, wherein each integrating sphere comprises at least one LED with identical wavelength and with different spatial positioning within the optical measuring device.
    [6]
    6. - Device according to any of the preceding claims, wherein the lens (6) has a width at least twice the width of the beam at the position of said lens (6).
    [7]
    7. - Device according to any of the preceding claims, comprising a second rectangular diaphragm (7) to limit the field of vision of the second measuring photodetector (8), located adjacent to the lens (6) and aligned with it in the path of the reflected beam.
    [8]
    8. - Device according to the previous claim, where the side of smaller length of the second rectangular diaphragm (7) is located perpendicular to the plane of incidence (9 ’) of the light beam on the surface (1) to be measured.
    [9]
    9. - Device according to any of the preceding claims, comprising at least two optical channels, wherein each optical channel is equipped with at least two emission LEDs in different wavelengths.
    [10]
    10. - Device according to the preceding claim, comprising between two and ten LEDs whose wavelengths are selected from one or more of the following:
    395, 435, 525, 650, 780, 850, 940, 1050, 1300 and / or 1550 nm.
    [11]
    11. - Measurement system for the reflection coefficient of a surface (1), comprising a measuring device according to any of the preceding claims connected to:
    - a circuit configured to perform the functions of analogue / digital acquisition and conversion of the signals detected by the photodetectors;
    - a signal processing circuit configured to process and extract the signal from the possible background of ambient optical and electrical noise;
    - a central processing unit internal or external to the device, which controls the overall operation of the system, and configured to select the electronic components corresponding to the channel used and govern internal and external communications to the device;
    - an insulation housing of the electronic and optical components of the
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    system.
    [12]
    12. - System according to the preceding claim, which comprises software implemented in the central processing unit for the communication of the device with it, and for the treatment of the information acquired by the measuring device.
    [13]
    13. - System according to any of claims 11-12, comprising an interface for communicating with the user via keyboard and / or screen.
    [14]
    14. - System according to any of claims 11-13, comprising a means of communication with a computer, tablet, or mobile device external to said system.
    [15]
    15. - Method for measuring the reflection coefficient of a surface (1), comprising the use of a measuring device according to any of claims 1-9, and where the following steps are performed:
    - the device is positioned so that it rests stably on the surface (1);
    - at least two LEDs (2) of each optical channel are illuminated, each of the LEDs (2) of the same channel being modulated at a different frequency, and the measurement of the reflection coefficient being made at their corresponding wavelengths;
    - the result obtained in the reflection detector (8) corresponding to the LED (2) modulated at a frequency is normalized, compared with a reference measurement at that frequency, to eliminate the influence of the variations in the emission intensity of each LED (2), obtaining a normalized reflection coefficient of the surface (1) for each measurement wavelength.
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    同族专利:
    公开号 | 公开日
    MA41924A1|2018-09-28|
    WO2017017297A1|2017-02-02|
    CN108449967A|2018-08-24|
    MA41924B1|2019-03-29|
    ES2603650B1|2017-09-05|
    ZA201800744B|2018-12-19|
    CL2018000146A1|2018-05-18|
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    FR2560377B1|1984-02-29|1988-05-13|Commissariat Energie Atomique|OPTICAL DEVICE FOR MEASURING SURFACE PROXIMITY AND ITS APPLICATION TO MEASURING A SURFACE PROFILE|
    JPH04329334A|1991-05-01|1992-11-18|Olympus Optical Co Ltd|Refraction factor distribution measuring device|
    ES2372191B1|2010-02-25|2012-09-06|Abengoa Solar New Technologies, S.A.|PORTABLE SPECTROPHOTOMETER AND METHOD OF CHARACTERIZATION OF SOLAR COLLECTOR TUBES.|
    ES2375386B1|2010-07-21|2012-09-27|Abengoa Solar New Technologies, S.A.|PORTABLE REFLECTOMETER AND METHOD OF CHARACTERIZATION OF MIRRORS OF THERMOSOLAR POWER STATIONS.|
    ES2366290B1|2010-10-20|2012-08-27|Abengoa Solar New Technologies S.A.|SPECTROPHOTOMETER FOR AUTOMATIC OPTICAL CHARACTERIZATION OF SOLAR COLLECTOR TUBES AND OPERATING METHOD.|
    CN102539387A|2011-12-28|2012-07-04|北京奥博泰科技有限公司|Method and device for measuring glass reflectance|
    ES2533778B1|2013-09-13|2016-02-02|Abengoa Solar New Technologies S.A.|Spectrophotometer for characterization of solar collector receivers|
    CN204255502U|2015-01-14|2015-04-08|中国计量学院|A kind of reflective spectral measure instrument based on LED light source|
    CN104792710B|2015-04-13|2018-08-03|杭州远方光电信息股份有限公司|A kind of object optical characteristic measuring device|FR3073943B1|2017-11-22|2020-05-29|Commissariat A L'energie Atomique Et Aux Energies Alternatives|MONITORING DEGRADATION AND FOULING MONITORING SYSTEM|
    CN110646169B|2019-10-28|2022-03-08|沈阳仪表科学研究院有限公司|Method for measuring reflectivity of curved surface optical film element|
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    优先权:
    申请号 | 申请日 | 专利标题
    ES201531138A|ES2603650B1|2015-07-30|2015-07-30|DEVICE AND SYSTEM OF OPTICAL MEASUREMENT OF THE COEFFICIENT OF REFLECTION OF A SURFACE|ES201531138A| ES2603650B1|2015-07-30|2015-07-30|DEVICE AND SYSTEM OF OPTICAL MEASUREMENT OF THE COEFFICIENT OF REFLECTION OF A SURFACE|
    CN201680059109.XA| CN108449967A|2015-07-30|2016-07-13|The device and system of optical measurement for surface reflection coefficient|
    PCT/ES2016/070531| WO2017017297A1|2015-07-30|2016-07-13|Device and system for optical measurement of the reflection coefficient of a surface|
    MA41924A| MA41924B1|2015-07-30|2016-07-13|Apparatus and system for optical measurement of the reflection coefficient of a surface|
    CL2018000146A| CL2018000146A1|2015-07-30|2018-01-18|Device and optical measurement system of the reflection coefficient of a surface|
    ZA2018/00744A| ZA201800744B|2015-07-30|2018-02-05|Device and system for optical measurement of the reflection coefficient of a surface|
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