Development of a low cost sun sensor using quadphotodiode

This paper describes about the design and hardware implementation of a low cost model of a two axis sun sensor using a quad photo diode, which can determine the azimuth and elevation angles of Sun in sensor's body frame of reference. The sensor uses quad photodiode to obtain angular information of Sun. It weighs less than 100g (which can be further reduced by optimizing the housing design). The relevant software requires 50K bytes of memory and little processing. We have also developed sensor calibration test bed (SCTB) which will also be the part of this paper. SCTB is used to calibrate the developed Sun Senor; during calibration the whole surface of sun sensor (quad photodiode) is scanned for a field of view (FOV) equal to 60 × 60. Step size during calibration is set to one degree so we get elevation and azimuth matrices each having 3721 values. The calibration process is fully automated with the help of algorithms written in Matlab. The step size used in calibration is adjustable and we can calibrate the sensor even less than one degree using this SCTB. Azimuth and elevation matrices generated during calibration are used as error correcting tables during real-time measurements taken by the sun sensor. Sun sensor is calibrated in front of Sun simulator made by the Optical Energy Technologies USA.