Jun 26 2013
A sun sensor is a device that senses the direction to the Sun to measure the position of the sun or other light sources with respect to the sensor position.
Sun sensors are usually classified into three types:
- Analog sensor whose output signal is a continuous function of Sun angle.
- Sun presence sensor which provides a constant output signal when the sun is in field of view.
- Digital sensor that produces encoded discrete output that is measured by the sun angle function.
The sun sensor is operated based on the entry of light into a thin slit on top of a rectangular chamber whose bottom part is lined with a group of light-sensitive cells. The chamber casts an image of a thin line on the chamber bottom. The cells at the bottom measure the distance of the image from a centerline and determine the refraction angle by using the chamber height.
The cells are operated based on the photoelectric effect. They convert the incoming photons into electrons and hence voltages which are in turn converted into a digital signal. When two sensors are placed perpendicular to each other, the direction of the sun with reference to the sensor axes can be calculated.
Sun sensors are widely used in spacecraft altitude determination systems for measuring the sun vector in spacecraft coordinates. They are also used for or orbit control and attitude control of spacecraft.
Other major uses of sun sensors include:
- Meteorological systems such as photovoltaic plant management, weather platforms, etc.
- Tracking systems such as parabolic trough, solar trackers, heliostats, etc.
- Navigations systems like observation balloon, unmanned vehicles, etc.
Products on Market
Some of the sun sensors that are currently available in market include the following:
Sun Sensor ISS-AX (Analog)
ISS-AX Sun Sensor developed by Solar MEMS has been designed with a novel technology based MEMS fabrication processes to measure incident angle of a sun ray by providing analog outputs. High reliability and low power consumption characteristics of this sensor have made it suitable for highly accurate sun-tracking and positioning systems.
Coarse Bi-Axis Sun Sensor
Astrium’s Bi-axis Sun Sensor is a simple analog sensor that measures sun’s angle by comparing intensities of two silicon solar cells within the sensor. It features four pairs of solar cells, a printed circuit board and an aluminum support block. The equipment body provides ±90° field of view (FOV) on each measurement axis, and the FOV can be reduced by the addition of specific external baffles to protect from straylight.
The key benefits of Bi-axis sun sensor include:
- Low cost
- High strength
- High temperature range
- Standard FOV.