Sun sensor
As a solar sensor are sensors indicated that the direction of the sun determine or the strength or duration of solar radiation.
House technic
In modern houses, shading is often automated via roller shutters or external venetian blinds depending on the amount of sunlight. Otherwise there is a risk of overheating in summer, especially with passive houses .
Photovoltaics
In photovoltaic systems can indeed be very beneficial over the calculated time and date Sun set the optimal orientation to the sun, but there are also solutions in which the panels are rotated through a solar sensor in the sun. The bandwidth ranges from simple analog differential controls to solutions with slit / point masks and CMOS image sensors .
automobile
Sun sensors are most widespread in cars - there, the cooling capacity of the air conditioning system can be individually pre-controlled for the occupants (driver / front passenger) depending on the position (and intensity) of the sun relative to the vehicle. Such a sun sensor usually consists of at least two light-sensitive sensors ( LDR , photodiode ) that are oriented in different directions - or are sensitive in different directions via optics. The difference between the two output signals gives a measure of the deviation of the sun's position from the center line of the sensors, the mean value of the signals gives a measure of the sun's intensity. The sensor is usually placed in the middle of the dashboard in the cover of the center speaker or the windshield air outlet under an infrared- permeable cover.
Space travel
In space travel , sun sensors are very often used individually or in groups (e.g. six for Mariner 1 and 2 and 16 for the Mars Reconnaissance Orbiter ) as position sensors for position control of satellites or their solar cell booms . You determine the position of a satellite relative to the sun . In principle, this is only possible if the sun is in the field of view (FOV ) of the sensor, but this only restricts its use in satellite orbits close to the planet. In this case, measures must also be taken to suppress interference from the reflection of sunlight by the planet.
A distinction is made between digital and analog sun sensors.
Analog sun sensors are mostly used for coarse control (e.g. shortly after take-off) or as a backup system for the satellite. They are characterized by their simple structure, quick detection and large detection range (45 to 180 °). A disadvantage is the relatively poor accuracy (depending on the functional principle) (e.g. 10 ° for the GOCE satellite ). Simple thermal radiation measuring devices (e.g. based on temperature-dependent resistances) or photo sensors are usually used as the measuring system. These are attached to all three sides (spatial directions) of the satellite and only determine (by comparing the values of the sensors) the direction of the greatest light irradiation. Sensors that work with two photo elements per sensor and perform a differential measurement between the two photo elements to determine the direction are somewhat more complicated. For this purpose, the mechanical-optical structure enables directional determination. This can e.g. B. a right-angled arrangement of the photo elements or an arrangement side by side with a vertical partition or a similar element casting shadows. With an even more complicated (more precise) structure, however, analog position sensitive devices or digital sensors with AD conversion are also possible.
In principle, digital sun sensors are based on digital position sensitive devices or image recognition systems, i.e. the detection of the sun with the help of line or matrix sensors (CCD or CMOS camera sensors), which allows a much more precise position determination (e.g. 0.02 ° at 128 ° detection range for the GOCE satellite ).
So-called slot sensors are often used for line sensors and for some analog sun sensors. With them, the sunlight falls through a narrow slit (the detection area depends on the length of the slit) onto the sensor arrangement, which is aligned perpendicular to it. With the line sensors, mostly several lines with increasing resolution (binary or gray code ) of the photosensors in the direction of the slot are used. Since the line sensors only determine one axis, at least two of them must be available, or a V-shaped slot with special evaluation software is used.
The fundamental disadvantage of all sun sensors is that only a two-dimensional determination of the position of the satellites is possible. The third spatial direction (angle to the earth) must be determined by additional sensors (e.g. earth sensors , horizon sensors or magnetic field sensors ). Their advantages are their high reliability and their low weight (<0.5 kg) and dimensions.
meteorology
In meteorology , sun sensors based on photo elements are used to determine the duration and intensity of sunshine .
Web links
- NASA: Spacecraft Sun Sensors (PDF; 2.6 MB)
- Free Patents Online: Three-axis-stabilized earth satellite and corresponding sun and earth acquisition maneuvers
Individual evidence
- ↑ Instructions for sun followers with LEDs as sensors on redrok.com (accessed on March 12, 2010)
- ↑ Paper ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 798 kB) on the construction of a sun position sensor with CMOS image sensor (accessed on March 12, 2010)
- ↑ Bernd Leitenberger: Mariner 1 and 2
- ↑ GOCE project page: Earth and sun sensor
- ↑ GOCE project page: Sun sensors
- ↑ Institute of Atmospheric Physics: Low cost Sun-Sensor (PDF; 11 kB)
- ↑ Cubesat: Cubesat Sun Sensor (PDF; 950 kB)
- ↑ TU Berlin - Institute of Aerospace: Position control of satellites ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
