DE102009045031A1 - Radiation sensor for solar panels - Google Patents

Abstract

A radiation sensor for detecting the position of the sun comprises a sensor housing with several bores arranged at an angle to one another, in which LEDs are fixed. Due to their very narrow beam bundling, the LEDs can be used as extremely precise position sensors. In addition, soiling of a cover of the sensor can be easily recognized. For this purpose, one LED is operated as a light source, while the other LEDs measure the reflected light. With this sensor, solar collectors can be aligned extremely precisely.

Description

Technical area

The invention relates to a radiation sensor, in particular a light sensor for determining the position of a radiation source. In particular, it relates to a sun sensor with which the exact position of the sun can be determined. By such a sensor, for example, solar systems can be optimally aligned with the sun.

State of the art

In the US 5,117,744 a sun sensor is disclosed, as it can be used for example for controlling the air conditioning of motor vehicles. The sunlight falls through an aperture on an area of solar cells divided into four partial areas. Depending on the position of the sun, different solar cells or parts thereof are illuminated. The electricity generated from the solar cells can also be used to determine the intensity of solar radiation.

The US 4,711,998 discloses another sensor with which the position of the sun can be determined with higher accuracy. Here are three solar cells, which are each shaded by mirror surfaces of each other, used and evaluated their signals mathematically to calculate the sun's position.

The US 7,378,628 B2 discloses another solar sensor in which four optical sensor elements are separated from each other by shading surfaces.

A disadvantage of the aforementioned sensors is that they each require a high outlay on production. Thus, in order to obtain sufficient sensor accuracy, the positioning of the individual sensor elements and the shading elements must be carried out with high precision. In order to achieve a high angular resolution, high shading elements are necessary, resulting in a relatively large design of the sensor. Furthermore, these sensors are not able to detect contamination on the sensor surface.

Presentation of the invention

The invention has for its object to provide a radiation sensor, in particular a light sensor, which has a high precision and at the same time cost manufacturable. Furthermore, the sensor should be able to detect contamination on the surface of a sensor cover and, if necessary, to correct the measured values accordingly.

This object is achieved by a device according to one of the independent claims. Advantageous embodiments of the invention are specified in the subclaims.

A radiation sensor according to the invention serves to detect the position of a light source or heat source. In particular, the position of the sun should be detected with such a sensor. Solar collectors, optional photoelectric collectors such as solar cells or thermal collectors or optical collectors have the best efficiency when they are aligned with the sun. In particular, in optical collectors in which sunlight is bundled by lens systems in optical fibers and passed through them for further use, are relatively sensitive to deviations from the direction of the sun to the optical axis of the system. Therefore, particularly precise sensors for detecting the position of the sun are necessary here.

A radiation sensor according to the invention has a sensor housing 10 with holes 11a . 11b . 11c . 11d . 11z for receiving LEDs 20a . 20b . 20c . 20d . 20z , These holes are arranged at an angle to each other and have a diameter so that LEDs in a standard housing, for example, with 3 mm or 5 mm in diameter can be used in this. A basic idea of the invention is that LEDs can basically also be operated as photosensors. Like photodiodes, they can emit a low photo voltage when exposed to light. Alternatively, upon exposure of the LED in the reverse direction, a radiation-dependent photocurrent will flow through the LED. Both effects can be used to generate a measurement signal. Compared to photodiodes, the efficiency and sensitivity of LEDs is much lower. However, this does not matter because with a sun sensor, a light source with relatively high radiation intensity must be detected. Furthermore, in contrast to conventional photodiodes, which are usually designed for a wide light entrance angle, LEDs are often also available for extremely small radiation angles. These are then used for example to a point-like lighting. By using such LEDs with a narrow light exit exit angle, a very narrow bundling of the characteristic is achieved during operation as a light sensor. In order to obtain a precise sensor, these strongly focusing LEDs have to be installed extremely precisely in a sensor arrangement. This is done by fixing the LEDs in holes of the sensor housing. As these LEDs are available inexpensively in precise standard housings, the sensor housing requires only a correspondingly positioned, precise hole to accept an LED. The LED can now easily in used the hole, for example, pressed and / or also be glued, for example, with epoxy resin. To achieve a very high precision, you can adjust the LED before gluing.

It achieves a very precise arrangement of the LEDs with respect to the housing and thus also a precise optical design of the light sensor with minimal manufacturing effort. In order to increase the precision even further, the reception characteristic of individual LEDs or the entire sensor can be measured and corresponding correction values can be stored for later correction of the sensor measured values. With such sensors angle resolutions of better than 0.1 degrees could be achieved.

According to the invention, at least two LEDs are now arranged at an angle to each other, so that they can never stand at the same time with their central axis to the sun. The two LEDs must therefore not be arranged in parallel. Now always delivers that LED, which is closer to the sun, the larger signal. Because of these signals, it is now easy to control a servomotor or other positioning device for positioning of the solar collector, so that both LEDs emit the same signal and thus both are equidistant from the sun, because then the sun is exactly in the middle between the LEDs.

Furthermore, a control unit is provided according to the invention, which evaluates the signals of the LEDs and / or optionally controls the LEDs, so that they emit light. It is obvious that an LED which is being driven to emit light can not be used simultaneously for the detection of light. However, it is possible to switch the LEDs in a clocked operation between light emission and light detection. Alternatively, different LEDs may emit light while other LEDs simultaneously detect light.

The main task of the radiation sensor according to the invention is to generate a control signal for the adjustment of a solar collector. In this case, the radiation sensor is preferably adjusted or aligned synchronously with the solar collector, so that the direction of incidence of the sunlight on the radiation sensor is parallel to the direction of incidence on the solar collector. For this purpose, the radiation sensor according to the invention has the maximum resolution in a central axis of the sensor, which preferably identical to the housing center axis 13 is. In principle, however, such a sensor can also be used for position determination relative to its central axis.

Radiation sensors according to the invention optionally have two, three or even four LEDs. In principle, more LEDs are possible. A sensor with two LEDs allows the tracking of a solar collector in one axis. With a sensor with three or four LEDs, tracking in two axes is possible. In the case of a sensor with three LEDs, these are preferably arranged around the housing center axis, offset by 120 ° relative to each other, at a constant distance from the housing center axis. In the case of a radiation sensor with four LEDs, however, these are arranged offset from each other by only an angle of 90 °, as in the arrangement with three LEDs.

In order to achieve the highest possible angular resolution of the sensor, the LEDs have a correspondingly small radiation angle. This should be less than 30 °, preferably less than 10 °. By selecting suitable LEDs, the sensor can be easily adapted to different resolutions with the same mechanical structure.

In a further advantageous embodiment of the invention, the central axes of the LED relative to the housing center axis tilted by a certain angle to the outside. This angle preferably corresponds to half the radiation angle of the individual LEDs. It would also be conceivable to tilt inwards so that the radiation lobes of the LEDs intersect.

In a further advantageous embodiment of the invention, the radiation sensor has at least one darkened LED. This LED is preferably permanently darkened, for example in a dark housing interior 12 integrated. The output signal of this LED is used to increase the measuring accuracy. Thus, for example, a dark current generated by this LED can be subtracted from the signal currents of the LEDs used for the measurement. This makes it easy to achieve a temperature compensation of the device. Such temperature compensation is particularly important because solar panels and thus the radiation sensor is exposed to direct sunlight and thus will heat up significantly during operation. In order to reduce the heating, preferably the part of the sensor housing facing the sun is reflective coated or mirrored.

In a further embodiment of the invention, a fine sensor with high angular resolution is provided for precise positioning. Here, LEDs are preferably used with low radiation angles. Furthermore, a coarse alignment coarse sensor is provided. Here LEDs are preferably used with large radiation angles. First, the coarse position of the radiation source with the Coarse sensor determined, then switched to the fine sensor to exact positioning. Instead of or in addition to the coarse sensor, a calculation of the position of the sun based on the location coordinates and the time can be done. If necessary, this information can be determined via satellite navigation, such as GPS (Global Positioning System). By comparing with the desired sun position from these values, a calibration of the sensor can also be carried out in a simple manner.

In a further advantageous embodiment of the invention, an additional photodiode and / or LED for day / night detection is provided. By a day / night detection, for example, at night the control unit 30 be deactivated to reduce the power consumption of the entire arrangement. Likewise, the solar collector can be driven into a sheltered night position.

According to a further embodiment of the invention is an additional LED 20z provided as a cloud sensor. This LED 20z is aimed directly at the sun. Accordingly, it is arranged parallel to the sensor central axis. By evaluating the ratios of the radiation intensity between the LED 20z as a cloud sensor and the other LEDs ( 20a . 20b . 20c . 20d ) can be determined whether the radiation is received diffused or strongly directed. In direct sunlight without clouds, the LED 20z As a cloud sensor generate a much higher signal than the other LEDs. With diffuse radiation, the differences in the signals are much lower.

In a further embodiment of the invention is a control unit 30 provided which measuring amplifier 34a . 34b and further means for measuring or evaluating the signals of the LED has. Furthermore, optionally at least one power source 35a . 35b provided for applying at least one LED with power. As a result, at least one LED for light emission can be specifically controlled.

By controlling the LEDs for light emission, various operating states can also be signaled. Thus, for example, an LED, which just receives the maximum sun intensity, in intermittent operation (flashing) signal this. Alternatively, one or more LEDs with others, for example the lowest intensities, can be triggered for emitting light. This allows a simple adjustment of the entire device or a troubleshooting.

An inventive sensor is preferred for detecting the position of the sun, but can also be used for position detection of the moon and other, even artificial, light sources.

Another aspect of the invention relates to a method for calibrating a radiation sensor according to one of the preceding claims.

In a first step, at least one of the LEDs is turned on 20a . 20b . 20c . 20d a current is fed so that the at least one LED imitates light. It is particularly favorable if light is actually only fed into a single LED here. In a subsequent step, the signal from at least one of the other LEDs is measured. Thus, light which is imitated by one of the LEDs is at least partially reflected by contaminants on the surface of the sensor or a further overlying cover and can then be detected by the other LEDs which do not imitate light. According to pollution, more or less light is reflected and correspondingly large is the signal amplitude in the other LEDs.

In a further process step, which can be carried out after this or before the first step, the dark current, i. H. without light emission by an LED, measured.

In a concluding evaluation step, the difference between the measured signal with light emission of an LED and the measured signal without light emission of that LED is then evaluated. This difference is a measure of the contamination of the sensor. To carry out such a measurement, preferably only one LED is excited to emit light. In further measuring sequences, different LEDs for light emission can be excited and the corresponding signals of the other LEDs can be evaluated. Thus, even a localization of pollution is possible. Based on these measured values of the contamination, a correction of the sensor measured values can now take place. Alternatively or additionally, an error message can also be issued if the sensor is heavily contaminated.

This method is preferably carried out in a dark environment (night), since otherwise the radiated from the outside basic light intensity is too high.

An inventive sensor can advantageously be calibrated with the aid of a collector signal from the solar collector. This collector signal can be derived, for example, by measuring the energy, current or voltage delivered by a solar collector. Thus, in a first step, the rough sun position due to the calculated position of the sun and / or the uncalibrated sensors can be approached. Thereafter, the area around the sun can be scanned to determine the position of the maximum collector signal and thus the maximum efficiency of the collector. This position will then be considered the new one Center position of the sensor defined. The scanning of the Sun's environment can be controlled on a helical path, or also by an algorithm that seeks a local or global maximum, for example, by calculating the first and second derivative of the collector signal by location. At the point of the maximum, the sensor values are measured and calibration data is obtained therefrom. This calibration also compensates for tolerances in the mounting of the sensor with respect to the collector and tolerances in an optical system of the collector. Since the tolerances of the collector tracking, for example by mechanical play are often position-dependent, the calibration is preferably carried out at different positions in different positions of the sun. After the sensor has been calibrated, an optimal sun position can be quickly controlled by evaluating the sensor signals. A frequent adjustment of the solar collector as for calibration is then no longer necessary.

Another application of the sensor is in the application as a vibration or motion sensor. The sensor is mounted on a movable or stationary base. This can be, for example, a bridge or building or the vibrating part of an engine. The light source is located in a stationary or movable part of the arrangement. The light source should preferably be a laser or a light source with a small opening angle and fully illuminate the sensor. In the rest position of the arrangement, the sensor provides a zero signal. If the surface begins to oscillate or move with the sensor, a signal is to be measured at the sensor output. The sensor should always be completely in the light cone of the light source in order to visualize the vibration or movement well. The distance from the sensor to the light source can be arbitrarily large.

Description of the drawings

The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawings.

1 shows a device according to the invention in section.

2 shows a perspective view of a device according to the invention with four LEDs.

3 shows an arrangement like 2 , but with an additional LED as a cloud sensor.

4 shows the radiation patterns of LEDs of the sensor.

5 shows a sensor arrangement with lower sunk LEDs.

6 shows a plan view of a sensor with 2 LEDs.

7 shows a plan view of a sensor with 3 LEDs.

8th shows a plan view of a sensor with 4 LEDs.

9 shows a plan view of a sensor with 4 LEDs and cloud sensor.

10 shows the block diagram of a complete sensor assembly with control unit.

In 1 a radiation sensor according to the invention is shown in section.

The sensor housing 10 includes the holes 11a and 11b for receiving the LEDs 20a and 20b , The LEDs are designed here in the typical 5 mm LED housing. The holes have a diameter so that the LEDs can just be pressed into them. The central axes 21a . 21b the LED 20a . 20b are at an angle to the housing center axis 13 arranged. For contacting the LED is located in the housing interior 12 another circuit board 14 , Of course, the LEDs can also be connected directly with cables or wires. Advantageously, on this circuit board 14 also the control unit or at least a part thereof arranged.

In 2 is shown a perspective view of the radiation sensor according to the invention. In the sensor housing 10 are four LEDs 20a . 20b . 20c . 20d in the holes 11a . 11b . 11c . 11d arranged.

In 3 is a radiation sensor with an additional LED 20z represented as a cloud sensor. This LED 20z is with its central axis 21z parallel to the central axis 13 of the sensor housing 10 arranged.

In 4 are the radiation patterns 22a . 22b the LEDs 20a . 20b shown. The emission angle is defined as the angle at which the radiation power is compared to the radiation power on the central axis 21a . 21b has dropped to half. The central axes 21a . 21b are opposite the housing center axis 13 tilted outwards. In these examples, the sensor center axis lies on the housing center axis. Therefore, in the presentation between these two terms is often not distinguished. Essential here, however, is the sensor centerline.

In 5 a further embodiment of a radiation sensor according to the invention is shown. Due to the good bundling by the LEDs shading, as known from the prior art, is not necessary. However, side lobes may appear on two LEDs in the radiation pattern. In order to prevent or at least reduce undesirable radiation entry through these side lobes here, the LEDs can penetrate deeper into the holes 11a . 11b of the housing 10 be sunk. This results in a simple way, a further shading.

In 6 is still a plan view of the radiation sensor, according to the invention in one embodiment, shown with two LEDs.

In 7 another embodiment of the invention is shown with three LEDs. These LEDs 20a . 20b and 20c are at a constant distance from the housing center axis 13 , Each offset by an angle of 120 ° to each other.

In 8th another embodiment of the invention is shown with four LEDs. These LEDs 20a . 20b . 20c and 20d are at a constant distance from the housing center axis 13 , Each offset by an angle of 90 ° to each other.

In 9 another embodiment is shown with a cloud sensor. The LED 20z as a cloud sensor is mounted here in the middle of the arrangement and has thus aligned with optimal orientation of the sensor their beam axis directly to the sun.

In 10 is still a control unit 30 shown to which LEDs 20a . 20b are connected. For evaluation of the signals of the LEDs 20a and 20b are measuring amplifiers 34a . 34b intended. These amplify the signals to a level that can be converted and processed by a microcontroller or an upstream analog / digital converter. Furthermore, there are power sources 35a . 35b for charging the LEDs 20a . 20b provided with a current for light emission. These power sources are controlled by the microcontroller 31 driven. Here is basically a control by digital signals, so that the LED can be switched on or off or even a control by analog signals, for example via a digital / analog converter possible. It is also not mandatory that each LED can be powered by a power source. However, it is very advantageous if this is possible at least for one LED. In principle, separate LEDs for light emission could also be used to detect contamination of the sensor from the measuring LEDs. For storing measurement data, which indicate contamination or on further calibration data, is still a calibration data memory 32 intended. This can either be integrated directly into the microcontroller or be implemented as an external memory chip. The output signal of the microcontroller 36 can then be used to control the solar collector.

LIST OF REFERENCE NUMBERS

10

sensor housing

11a, b, c, d

Bore for LED

12

Housing interior

13

Housing center axis

14

circuit board

20a, b, c, d, z

LED

21a, b, z

Central axis of the LED

22a, b

lobe

30

control unit

31

microcontrollers

32

calibration data

34a, b

measuring amplifiers

35a, b

power source

36

output

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5117744 [0002]
• US 4711998 [0003]
• US 7378628 B2 [0004]

Claims (17)

Radiation sensor for detecting the position of a light source comprising - a sensor housing ( 10 ) with at least two at an angle to each other arranged holes ( 11a . 11b . 11c . 11d ), - at least two LEDs ( 20a . 20b . 20c . 20d . 20z ), which are fixed in each case one of the holes, - a control unit ( 30 ) for controlling the LED ( 20a . 20b . 20c . 20d . 20z ) and / or evaluation of the signals of the LED ( 20a . 20b . 20c . 20d . 20z ). Radiation sensor according to claim 1, characterized in that the radiation sensor 3 LED ( 20a . 20b . 20c ), which are arranged offset by 120 degrees relative to each other about the housing center axis. Radiation sensor according to claim 1, characterized in that the radiation sensor 4 LED ( 20a . 20b . 20c . 20d ), which are arranged offset by 90 degrees relative to each other about the housing center axis. Radiation sensor according to one of the preceding claims, characterized in that the LEDs have a radiation angle of less than 30 degrees, preferably 10 degrees. Radiation sensor according to one of the preceding claims, characterized in that the central axes ( 21a . 21b ) of the LED ( 20a . 20b ) with respect to the housing center axis ( 13 ) at an angle corresponding to half the beam angle of the LED ( 20a . 20b ) are tilted. Radiation sensor according to one of the preceding claims, characterized in that the radiation sensor comprises at least one darkened LED whose output signal is used by the control unit to increase the measurement accuracy. Radiation sensor according to one of the preceding claims, characterized in that at least the light source facing part of the sensor housing radiation reflective, preferably mirrored. Radiation sensor according to one of the preceding claims, characterized in that a first radiation sensor is provided with low angular resolution for approximate position determination and a second radiation sensor with high angular resolution for exact position determination. Radiation sensor according to one of the preceding claims, characterized in that an additional comparison of the sensor values with reference data of the light source, in particular the sun or the moon is carried out, which were preferably determined from local and time information or by means of satellite navigation. Radiation sensor according to one of the preceding claims, characterized in that an additional photodiode for day / night detection is provided. Radiation sensor according to one of the preceding claims, characterized in that an additional LED ( 20z ) is provided as a cloud or obscuration sensor. Radiation sensor according to one of the preceding claims, characterized in that at least one of the LEDs ( 20a . 20b . 20c . 20d . 20z ) can be charged with a current and thereby excited to emit light. Radiation sensor according to one of the preceding claims, characterized in that the control unit ( 30 ) Measuring amplifier ( 34a . 34b ) as well as further means for measuring and evaluating the signals of the LED ( 20a . 20b . 20c . 20d . 20z ) and / or at least one power source ( 35a . 35b ) has for energizing at least one LED with power. Radiation sensor according to one of the preceding claims, characterized in that it is operated as a vibration or motion sensor with a separate light source. Radiation sensor according to one of the preceding claims, characterized in that the light source for the radiation sensor has a small opening angle and preferably fully illuminates the radiation sensor. Method for calibrating a radiation sensor according to one of the preceding claims, comprising the steps: - feeding a current into at least one of the LEDs ( 20a . 20b . 20c . 20d . 20z ) so that the at least one LED emits light; - Measuring the signal from at least one of the other LED, which has not been subjected to a current for the emission of light; - Evaluation of the difference of the signals from at least one of the other LED with and without light emission of the light emitting LED. Method for calibrating a radiation sensor according to one of the preceding claims by evaluating the collector signal of a solar collector connected to the sensor, comprising the steps of: - coarse positioning of the solar collector; Iteratively measuring the collector signal and changing the position of the solar collector until the collector signal has reached a maximum; - Measuring the sensor values and generating calibration data.

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