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WO2015162322A1 - A dirt sensor and method for detecting the amount of dirt on a surface - Google Patents

A dirt sensor and method for detecting the amount of dirt on a surface

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Publication number
WO2015162322A1
WO2015162322A1 PCT/ES2015/070308 ES2015070308W WO2015162322A1 WO 2015162322 A1 WO2015162322 A1 WO 2015162322A1 ES 2015070308 W ES2015070308 W ES 2015070308W WO 2015162322 A1 WO2015162322 A1 WO 2015162322A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
light
surface
dirt
transparent
sensor
Prior art date
Application number
PCT/ES2015/070308
Other languages
Spanish (es)
French (fr)
Inventor
OSTIATEGUI Roberto CALVO
BURGOS David CANTERO
Original Assignee
Fundación Tekniker
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/84Systems specially adapted for particular applications
    • G01N21/88Investigating the presence of flaws or contamination
    • G01N21/94Investigating contamination, e.g. dust
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24JPRODUCING OR USE OF HEAT NOT OTHERWISE PROVIDED FOR
    • F24J2/00Use of solar heat, e.g. solar heat collectors
    • F24J2/46Component parts, details or accessories of solar heat collectors
    • F24J2/4607Safety or protection arrangements; Arrangements for preventing malfunction; Auxiliary devices, e.g. means for testing
    • F24J2/461Means for cleaning or for removing snow
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24JPRODUCING OR USE OF HEAT NOT OTHERWISE PROVIDED FOR
    • F24J2/00Use of solar heat, e.g. solar heat collectors
    • F24J2/40Control arrangements
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/84Systems specially adapted for particular applications
    • G01N21/88Investigating the presence of flaws or contamination
    • G01N21/94Investigating contamination, e.g. dust
    • G01N2021/945Liquid or solid deposits of macroscopic size on surfaces, e.g. drops, films, or clustered contaminants
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GASES [GHG] EMISSION, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/40Solar thermal energy

Abstract

The invention relates to a sensor (20) for detecting the amount of dirt on a surface, said sensor comprising: a transparent surface (21) exposed to dirt; a light emitter (22) for emitting a beam towards the transparent surface; a first light receiver (23) and a second light receiver (25); means (24) disposed between the light emitter (22) and the transparent surface (21) and configured to allow part of the light from the emitter to pass towards the transparent surface (21) and to re-direct the rest of the light towards the second receiver (25); acquisition and processing means (26). The first light receiver (23) is configured to receive light diffused upon impact with dirt on the external face (21e) of the transparent surface (21). The acquisition and processing means (26) are configured to calculate a percentage measurement of the degree of dirt on said transparent surface (21).

Description

A DIRT SENSOR AND METHOD FOR DETECTING THE AMOUNT OF DIRT ON A SURFACE

Field of the Invention

The present invention belongs to the field of sensors of dirt or dust, and more particularly, to the field of sensors dirt on surfaces, whether flat, curved, or other rough features. An application of dirt of the invention sensor is measuring dirt concentrating mirrors solar power plants.

BACKGROUND OF THE INVENTION

There is currently a great interest in making large solar power plants to generate energy. One of the most advanced technologies is based tower technology plants. The technique uses a set of mirrors or reflective surfaces (called heliostats) that track the sun and concentrate solar radiation in one or more receptors found in the top of a tower. From the receiver or receivers heat is transferred to a heat transfer fluid, for example water, which will be vapor source to turn produce electricity. This technology is very efficient due to the high temperatures that can be operated. Also noteworthy are the parabolic trough technology, based on a set of mirrors parabolic (parabolic concentrators, CCP) placed on a structure so that they can follow the movement of the sun. Solar radiation collected is concentrated on a receiver tube leading inside a fluid capable of absorbing heat. The fluid thus reaches high temperatures and transmits the heat energy to steam, which will be vapor source to turn generate electricity. Especially in the case of reflective surfaces intended for use in solar plants for generating power, the mirror interested take 100%. In this application, the heliostats are designed to be virtually flat. Possible defects that may occur are edge defects or corners, for example.

A key element in these plants are reflective surfaces that concentrate solar radiation, also called solar thermal concentrators. A control aspect in these reflective surfaces resides in the geometry, since the surfaces to concentrate the solar radiation in the region of interest, its shape should be adequate. Another fundamental aspect is its cleanliness, because any dust particles impairs the solar concentrator performance.

To determine dirt mirrors (generally in the reflective surfaces of the type mentioned in the previous paragraph), they are known reflectometers called commercial equipment, which allow to measure the loss of reflectivity of a mirror with high accuracy. Their main problem is that they are very expensive, partially interfere with the light to be reflected in the mirror, require precise mechanical adjustment to the surface and are susceptible to its optical capture dirt, which distorts the measure. US Patent US8323421 B2 describes an automatic cleaning system for solar panels comprising, among other elements, a sensing device capable of determining whether the solar panels need to be cleaned.

The international patent application WO2012 / 089485A1 describes a photovoltaic module that generates electricity from solar energy, which can detect dirt from its surface. The photovoltaic module is formed by a solar panel and detection means indicating the amount of dust and dirt accumulated on the solar panel. Detection occurs by a receptacle with a line parallel to the solar cell surface, a light source outside the receptacle, a sensor assembly inside the receptacle and a control unit to monitor the amount of light reaching the sensors and generate a distorted signal when the quantity of light is below a certain threshold.

DESCRIPTION OF THE INVENTION

The present invention provides a device and method capable of determining the amount of dust or dirt on its sensitive surface.

In a first aspect of the invention, a sensor is provided for detecting the quantity of dirt from a surface. The sensor comprises: a transparent surface which is exposed to dirt on its outer face; a light emitter configured to emit a light beam in a certain frequency range to the transparent whose dirt on its outside surface to be measured; a first light receiver configured to detect light in said predetermined frequency range; a second receiver configured to detect light in said light determined frequency range; means located between the light transmitter and the transparent surface, these being configured to pass a portion of the light from the light emitter toward the transparent surface and to redirect the rest of light from the light emitter to the second receiver means light; acquisition and processing means. The first light receiver is configured to receive said portion of the light from the light emitter that reaches the transparent surface, the diffused light striking the dirt of the outer face of the transparent surface. The acquisition and processing means are configured to calculate, from the light detected by the second light receiver and the light detected by the first light receiver, a percentage measure of the degree of soiling of the transparent surface.

Preferably, the means positioned between the light emitter and the transparent surface is a beamsplitter.

Preferably the light emitter is located in a plane forming an angle of α degrees to the plane in which is located the transparent surface, where the angle α varies between 30 and 60 and.

Preferably the first light receiver comprises a photodiode array.

Preferably, the means positioned between the light emitter and the transparent surface are located in a plane forming an angle of β degrees with the plane in which is located the light emitter, wherein said β angle varies between 30 and 60 and.

Preferably the light emitter is configured to emit a beam of light in the range of infrared light and the first and second light receivers are configured to detect light in the infrared light range. Preferably the means comprises acquisition and processing means for adjusting the extent depending on the temperature. Preferably the transparent surface is a glass.

In one possible embodiment, light dimmer before the second receiver is disposed. In another possible embodiment, the use of the sensor described above is provided for detecting the quantity of dirt from a concentrator mirror of thermal energy.

In another possible embodiment, a method is provided for detecting the quantity of dirt from a surface. The method has the steps of: emitting a beam of light in a given frequency range to a transparent surface which is exposed to dirt on its outer face; capture in a first light receiving scattered light striking the transparent surface dirt; diverting a portion of the emitted light before reaching the transparent surface to grasp a second light receiver to make said light deflected by reference; calculating from the light detected by the second light receiver and the light detected by the first light receiver a percentage measure of the degree of soiling of the transparent surface.

Finally, a computer program comprising code instructions computer program to perform the above method is provided.

Further advantages and features of the invention will be apparent from the following detailed description and pointed out in particular in the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

To complete the description and in order to aid a better understanding of the characteristics of the invention according to a practical embodiment thereof, accompanying as an integral part of the description, a set of drawings in which with character illustration and not restrictively, the following has been represented: figure 1 illustrates the operating principle of the sensor of the invention.

2A illustrates a schematic of the elements forming a device according to a possible embodiment of the invention. 2B shows a front exterior view of the device according to a possible embodiment of the invention. 2C shows a detail of the diagram of Figure 2A, which shows how the angle of reflection of the light reflected by the beamsplitter is equal to the angle of incidence of the beam incident on the beam splitter.

3 shows a block diagram of the electronic acquisition and processing according to a possible embodiment of the invention.

4 shows in detail the processing block signals provided by the receivers and reference measurement.

Description of an embodiment of the invention Figure 1 illustrates the operating principle of the sensor of the invention: by illuminating with a light source 12 dirt particles 1 1 deposited on a transparent surface 10, the light is diffused in various directions, increasing the amount of scattered light 13 in proportion to the amount of dust deposited on that surface. The light is emitted to the inside of the surface 10 (e.g., glass), so that the scattered light 13 by the dirt particles on January 1 deposited on the outside surface 10 is projected (dispersed) to an optical transducer (eg, a photodetector array) 14. The amount of light collected by these is proportional to the number of particles deposited on January 1. The optical transducer, controlled by a processing unit and signal processing (not shown), provides a measure corresponding to that amount.

The sensor of the invention, based on the principle of previous operation, is able to optimize a number of properties, namely: minimize interference from light sources (natural or artificial); minimize reliance on measurements with temperature; and maximize sensitivity.

2A illustrates a schematic of a device according to a possible embodiment of the invention. This is a sensor 20 for detecting dirt amount of dirt (dust or other particles) of a transparent surface 21 is exposed, on its outer face 21 and, dirt. The transparent surface 21 is preferably a transparent glass. In the scheme of Figure 2, the transparent surface 21 is substantially planar, but need not be so. By contrast, the surface 21 may be curved, rough or any other characteristic. The surface 21 acts as a dirt trap. In use of the device 20 as dirt sensor, the device can be placed beside a surface of interest, either flat, curved, rough, etc. The device 20 will indicate the amount of dust deposited on the surface presumably of interest, considering that is next to the sensor (and thus both will capture a similar amount of dust or dirt). Therefore, the device 20 serves to indicate that in the sensitive area (outer face 21 and surface 21) has captured a certain amount of dirt.

As generally it is shown Figure 2A, the sensor 20 comprises a transparent dirt surface 21 that is the sensitive area whose captured dirt to be detected, emulating what happens in an area whose dirt is to be controlled. One possible example of surface dirt which is to emulate, for which the device 20 is positioned close to the surface, is a mirror concentrator power. Thus, if dust deposits on the mirror, substantially the same as dust will be deposited on the transparent surface 21 of the sensor 20. By measuring the dust on the surface 21 of the sensor 20, it is extrapolated that approximately the same amount will be deposited in the concentrator mirror.

The dirt sensor 20 also comprises a light emitter 22, preferably infrared. Alternatively, the light emitter 22 may emit a different frequency or frequencies of the spectral range infrared, such as the visible spectrum, or other non-visible spectrum frequencies. This emitter 22 emits a light beam towards the inner surface 21 i of the transparent surface 21 whose dirt is to be measured. Preferably, the transmitter 22 is located in a plane forming an angle of α degrees relative to the sample plane (transparent surface 21). That is, the emitter 22 preferably not emitted from a flat surface parallel to the plane 21 .Preferentemente the α angle ranges between 30 and 60 and. In the exemplary implementation, we have chosen α = 45 e. Alternatively, the emitter 22 can emit its light beam substantially perpendicular to the transparent surface 21. In this case, the transmitter 22 is located in a plane substantially parallel to the transparent surface 21 (implementation not shown) plane.

The sensor 20 also comprises a light receiver or photodetector 23 configured to collect light in the same spectral range of the emitter 22. That is, if the emitter 22 emits a beam of infrared light, the receiver 23 is a receiver of infrared light. The light receiver 23 should be placed in that place / position to collect the maximum light scattered by dust / dirt deposited on the outside of the transparent surface 21. In one possible embodiment, illustrated in Figure 2A, the light receiver 23 is placed in a plane substantially parallel to the sample (transparent surface 21), the inner side 21 i in the same plane. The receiver 23 may be located alternatively in other positions, as long as it can substantially grasp therefrom the quantity of light diffused by the powder according to the sensitivity required for the particular sensor 21. This receiver 23 is preferably formed by a photodiode array. In a particular implementation, receiver 23 is implemented with an array of four photodiodes. The inventors have observed that the four photodetectors, whose effects are added, distributed over part of the area to which the scattered light is directed, provide high sensitivity for the particular geometry tested. The sensor 20 also comprises a beam splitter 24 (in English, beam splitter), located between the emitter 22 and the transparent surface 21 whose dirt is to be measured. The beamsplitter 24 must be placed in such a position that the light beam emitted by the emitter 22 to the surface 21 in its path to the beamsplitter 24.

The sensor 20 also comprises a receiver (photodetector) 25. Optionally the reference sensor 20 may have a dimmer 27 located ahead of the reference receiver 25 and preferably substantially parallel thereto. The attenuator 27 is used if necessary to avoid saturating the reference photodetector 25. The sensor 20 also has means 26 acquisition and processing, to interpret and process steps, as detailed in connection with Figures 3 and 4.

The operation of the sensor 20 is as follows: the emitter 22 projects light emitted on the inner face 21 i (protected for contamination outside) of the transparent surface 21 whose dirt is to be measured. The light emitted by the emitter 22 is on its way to the beam splitter 24, which must therefore be disposed between the emitter 22 and the transparent surface 21, so that the light beam emitted by the emitter 22 reaches the beam splitter 24. the splitter 24 passes to the flat surface a percentage of the emitted power, while redirects (deflects) the rest of the emitted power. 2C shows a detail of the diagram of Figure 2A, in which it is observed, as a skilled person knows, how the angle of incidence p, with respect to the perpendicular divider 24- incident beam from the emitter 22 is equal to reflection angle p of the light reflected or deflected by the beamsplitter 24. This power offset is detected by the reference photodetector 25. therefore, the reference photodetector 25 could be placed in any position, provided it is able to capture radiation deflected by the beamsplitter 24. This achieves obtaining a sample of the light signal emitted by the transmitter 22. the amount (percentage) of light passing through without deviating the beam splitter 24 to the transparent surface 21 and the amount (percentage) of light passing through without deviating the beam splitter 24 to the transparent surface 21 are dependent on the geometry of the beams and the concrete elements used in the sensor. For example, it can be designed sensor 20 so that the percentage of light passing through without deviating the beam splitter 24 to the transparent surface 21 is between 50% and 90%, while the percentage of light that is diverted to the reference photodetector 25 is between 50% and 10%. The reference photodetector 25 thus provides a measure of the actual intensity of the light generated by the emitter 22.

The light (the percentage of light that has passed up, without departing from the beam splitter 24) received at the transparent surface 21 (on its inner face 21 i) passing through said surface 21. If there is dirt on the outer surface 21 and the light colliding with dirt, diffuses toward the inner face 21 i, reaching photodetector array or measuring receiver 23. For this reason, the measuring receiver 23 must be placed in any position to capture the diffused radiation to hit the dirt. In the ideal that there was nothing of dirt on the outer face 21 case and there would be no light scattering and therefore all the light that came to the flat surface 21 of the traverse outward. However, in practice, even if the outer face 21 and were completely clean, the inner face 21 of the transparent surface i reflect a small part of the light into the sensor, behaving like a mirror. The amount of light reflected by this effect depends on the type of surface. The sensor 20 of the invention eliminates this effect using a parameter obtained in the calibration of the sensor. The arrangement of the emitter 22, beam splitter 24, sample surface 21 and the reference receiver 25 should be chosen so that a sufficient amount of power of the transmitter 22 reaches the sample surface 21 (eg, between 50% and 90%), a sufficient amount of power of the transmitter 22 arrives, redirected by the beam splitter 24, the receiver 25 (for example, between 50% and 10%) and that interferences are minimized between elements internal sensor 20. in a preferred embodiment, the beam splitter 24 is preferably located in a plane forming an angle of β degrees with respect to the plane in which is located the light emitter 22. preferably the angle β ranges from 30 and 60 e. In the exemplary implementation, it was chosen and β = 45. Given that, in the exemplary implementation, the reference receiver 25 is located at 90 and with the main beam emitted by emitter 22, this β = 45 and minimizes interference between the sensor elements.

In the exemplary implementation, it is selected a transparent substantially flat surface 21, but other surface could alternatively be chosen. In addition, the transparent surface is, in this example, of rectangular shape, as shown in Figure 2B. Also in the exemplary implementation, as transparent surface 21 has been chosen a substrate is used to manufacture parabolic concentrators, because an outstanding application of the invention sensor is detecting dirt in parabolic concentrators. It has chosen the same substrate to have the same level of grip.

Acquisition means and processing (electronic acquisition and processing) 26 controls first light emission (emitter 22) by a signal of sinusoidal current controlled which is generated digitally by a software component (for example, but in a non limited, executed at 4 kHz). As detailed in connection with Figures 3 and 4, electronic acquisition and processing acquires signals of the photodetectors measuring 23 and reference 25 and processed in a software component (in an example, but not limited to, is also executed at a frequency of 4kHz).

As noted above, sensor 20 minimizes interference from light sources (natural or artificial); minimizes dependence measures temperature; and maximizes sensitivity.

Interference sources external to the sensor (eg, sunlight) are minimized as explained below: First, the light source 22 is chosen within the spectrum so that its intensity exceeds the amount of light received from the sun in the same band of spectrum. Preferably, a source of infrared light is chosen. Second, the photodetectors 23 25 incorporate selective filters (infrared in the case that the emitter emits infrared light). Finally, the light source 22 is modulated with a relatively high frequency (for example, between 80 and 150 Hz). In one example, a modulated signal at 135 Hz is selected. This frequency is chosen that is high enough to reject possible sources of natural or artificial oscillating light, but at all times avoiding harmonics of 50Hz and 60Hz networks power, and so that is generated with a high resolution taking into account the sampling frequency of the generator. Since the light source 22 is modulated at a particular frequency, the part of the light scattered by dirt also oscillates at the same frequency. For this reason, the detection means 23 comprise a selective bandpass filter which allows only collect scattered light caused by the emitter 22 and not by other light sources. Measuring diffused light is thus always provided to the light itself emitted by the emitter 22 of sensor 20.

Regarding the effect on the measurements of the temperature change, it affects the sensor 20 in many aspects, including both the own electronic structure as the opto-mechanical assembly and emitting devices and infrared receivers. Therefore, the sensor 20 comprises means and techniques for thermal compensation. In particular, the sensor 20 comprises means for thermal compensation in the sending and receiving devices infrared, where these thermal effects are particularly relevant. Infrared emitters have a high variation with temperature of the relationship between emitted light intensity and the applied current (gain variation around 0.5% / and C or higher). This variation also differs between different units of the same series of devices with the same product number. Also photodetectors exhibit gain variation with temperature, but to a lesser degree, and this is different entity different units of the same component. In addition, the photodetectors having a signal level in the dark or offset that varies with temperature. This "offset" is also different between different units of the same component.

Preferably, the sensor 20 minimizes the effect of the offset signal from the photodetectors 23 25 by art cited modulation and by means of demodulation and bandpass filtering which removes all contributions receiving continuous light in the received signal at all photodetectors 23 25.

Furthermore, the effect of gain variation in the emission source of light 22 is preferably minimized by a technique of differential photodetection: continuously measuring the emitted light (in the transmitter 22) and the diffuse light received (in the receiver is weighted 23) with respect to the emitted light. This technique also removes the variation component common gain of the two receivers (reference 25 and measure 23), but does not eliminate the difference in gain between the various components photodetectors. Preferably the effect of the gain difference between the photodetectors is minimized by a temperature transducer and a compensation algorithm.

Finally, the sensitivity is preferably maximized through selection and control of a light source 22, preferably infrared, high intensity and photodetection by a matrix of four photodetectors which add the current obtained in each of them and are also exposed to different detection areas diffuse light, thus adding light energy uptake in a greater area than a single photodetector. 3 shows a block diagram of a possible implementation of the acquisition and processing electronics 26. A Calib_Gain parameter allows the measuring range of the sensor. This parameter is obtained by the calibration process. Another parameter Calib_Bias eliminates the effects of diffusion of the emitted light generated by the own internal walls of the sensor 20 and the reflection effect of the inner face 21 of the surface 21 i. This parameter is also obtained by the calibration process. A processing block 261 performs demodulation of the two signals provided by photodiodes 23 measure (signal 2623) and 25 (signal 2625) and provides the equivalent measurement / reference ratio out_261 weighted information. A block 262 converts the values ​​of both 1 to 100 using the thus Calib_Gain parameter. A block 263 to modify the extent a function of temperature using an interpolation algorithm. Therefore enables correcting the gain difference with the temperature between photodetectors and other thermal drift, for involving a subsystem 265. Finally, block 264 performs statistical calculations of the extent a given period (averaged measured, maximum value, minimum value and standard deviation).

4 shows in detail a part of the processing block 261 of the signals provided by the measuring receivers 23 and 25. On the two reference signals 2623 2625 (from the two receivers 23 25) the same processing is performed: First the received signal by a retainer 2623 2625 or zero sampler 261 is 1 order. The resulting signal is processed by a bandpass filter 2612, preferably of order 8, and cutoff frequency centered on a frequency preferably ranging between 80 and 150 Hz (for example, 135 Hz). The signal thus obtained is rectified 2613 and subsequently treated by a lowpass 2614 preferably second order (eg 2 Hz cutoff frequency) filter. The result of this processing is the value of the amplitude of the measurement signals and 2614r 2614m reference. 2615 performing division between both the measurement / out_261 reference ratio corresponding therefore to a differential measurement (in which thermal influences disappear indicated above) is obtained. The processing block 261 further comprises other elements for detecting whether the measurement is incorrect. For simplicity, these additional blocks not shown in the diagram of Figure 4.

As has been seen, the dirt sensor 20 provides a percentage measure of the degree of cleaning (or debris) from the sample surface 21 exposed. This measure thus has a value of 0 when dirt is maximum and a value of 100 when dirt is minimal. The minimum dirt dirt maximalist terms set out in the calibration of the device, whereas the minimum is reached after cleaning dirt as much as possible the surface 21, while for maximum dirt can be considered different patterns of dirt or dissemination of light. Detecting dirt of any surface, for example a solar thermal concentrator mirror center, should the sensor 20 adjacent to the surface of interest. Whereas, due to proximity, the sample surface 21 of the sensor 20 will capture substantially the same amount of dirt that the surface of interest, the device 20 will indicate the amount of dust deposited on the surface presumably of interest.

The measurement process establishes an initial period of stabilization programmable from which the computer performs measures cyclically or periodically. The period between measurements is also programmable and is limited by the minimum time of acquisition and processing of measurement data. In a possible embodiment, this minimum period has been established in 10 seconds (optimized after experimental tests), while the measurement result of the sensor corresponds to averaging of the calculated measures the stationary time. Preferably, the measurement result of the sensor corresponds to averaging of the calculated measures in the second half of the acquisition period, when the demodulated signals reach stability.

Preferably, the calibration process involves two steps that define the dynamic range of the sensor. With the substrate (the transparent surface 21) completely clean, the first reference measurement which defines the maximum degree of cleaning identified with the 100% value is performed. For the second measurement, which is used as reference minimum cleaning, is deposited on the substrate the degree of contamination is identified with the value 0%. The end result of the process is a relative measure of dirt with a ranging between 0 and 100 so that the maximum value corresponds to the maximum relative cleanliness and the minimum value with relative minimal cleaning. To simplify access to measurement and calibration has developed a software application that enables real-time monitoring of the measurement process and modifying internal settings of the device. The application also has support mechanisms that simplify the calibration process.

It has developed a prototype which is fed with a voltage of 5 to 24V and has a MODBUS RTU via RS485 through which can access the measurement result and that allows setting operation parameters remotely.

The sensor described herein has particular application in the measurement and control of dirt concentrating mirrors solar power plants.

In this text, the word "comprises" and its variants (such as "comprising", etc.) should not be interpreted in an exclusive manner, that is, they do not exclude the possibility that what is described includes other elements, steps etc.

Moreover, the invention is not limited to the specific embodiments described but also covers, for example, the variants that can be carried out by a skilled person (for example, the choice of materials, dimensions , components, configuration, etc.), within what is deduced from the claims.

Claims

What is claimed
1 .- A sensor (20) for detecting the quantity of dirt from a surface, characterized by comprising: a transparent surface (21) is exposed to dirt on its outer face (21 e); a light emitter (22) configured to emit a light beam in a certain frequency range to said transparent surface (21) whose dirt on its outer face (21 e) to be measured; a first light receiver (23) configured to detect light in said predetermined frequency range; one second light receiver (25) configured to detect light in said predetermined frequency range; means (24) located between said light emitter (22) and said transparent surface (21), said means (24) being configured to pass a portion of light from said light emitter (22) to said transparent surface ( 21) and to redirect the rest of light from said light emitter (22) to said second light receiver (25); means acquisition and processing (26); first light receiver (23) configured to receive said portion of the light from the light emitter (22) that reaches the transparent surface (21), the light being said diffused striking the dirt on the outer side ( 21 e) said transparent surface (21); and said means of acquisition and processing (26) configured to calculate, from the light detected by said second light receiver (25) and the light detected by said first light receiver (23), a percentage measure of the degree being dirt of said transparent surface (21).
2. - The sensor (20) of claim 1, wherein said means (24) located between said light emitter (22) and said transparent surface (21) is a beam splitter.
3. -The sensor of any of claims 1 or 2, wherein said light emitter (22) is located in a plane forming an angle of α degrees to the plane in which is located the transparent surface (21), where said angle α varies between 30 and 60 and.
4. -ei sensor of any of the preceding claims, wherein said first light receiver (23) comprises a photodiode array.
5. -ei sensor of any of the preceding claims, wherein said means (24) located between said light emitter (22) and said transparent surface (21) are located in a plane forming an angle of β degrees with the plane on which it is located the light emitter (22), wherein said angle β varies from 30 to 60 e.
6. -ei sensor of any of the preceding claims, wherein said light emitter (22) is configured to emit a light beam in the range of infrared light and said first (23) and second (25) light receivers are configured to detect light in the range of infrared light.
7. ei sensor of any of the preceding claims, wherein said means of acquisition and processing (26) comprises means for adjusting the extent depending on the temperature.
8. EI-sensor of any of the preceding claims, wherein said transparent surface (21) is a crystal.
9. -The sensor of any of the preceding claims, further comprising a dimmer (27) disposed in front of the second receiver (25).
10. - Use of any of the preceding claims for detecting the amount of dirt from a concentrator mirror thermal energy sensor.
eleven . -A method for detecting the quantity of dirt from a surface, characterized by the steps of:
- emitting a beam of light in a given frequency range to a transparent surface (21) is exposed to dirt on its outer face (21 e);
- capturing a first light receiver (23) light scattered by colliding against dirt said transparent surface (21);
- diverting a portion of the emitted light before it reaches said transparent surface (21) to grasp a second light receiver (25), to make said light deflected by reference;
-Calculate, from the light detected by said second light receiver (25) and the light detected by said first light receiver (23), a percentage measure of the degree of contamination of said transparent surface (21).
12. Computer program comprising code instructions computer program for performing the method of claim 1 January.
PCT/ES2015/070308 2014-04-24 2015-04-17 A dirt sensor and method for detecting the amount of dirt on a surface WO2015162322A1 (en)

Priority Applications (2)

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ESP201430605 2014-04-24
ES201430605A ES2549395B1 (en) 2014-04-24 2014-04-24 Dirtiness sensor and method for detecting the quantity of dirt from a surface

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WO2015162322A1 true true WO2015162322A1 (en) 2015-10-29

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US5343290A (en) * 1992-06-11 1994-08-30 International Business Machines Corporation Surface particle detection using heterodyne interferometer
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