The Ørsted Satellite Project

A Danish Microsatellite With a High Scientific Profile

Papers and reports


MAGNETIC CALIBRATION OF VECTOR MAGNETOMETERS: LINEARITY, THERMAL EFFECTS AND STABILITY

 

Brauer, P. (1), J.M.G. Merayo (1), T. Risbo (2), and F. Primdahl (1,3)

 

  1. Technical University of Denmark, Department of Automation, Building 327, DK-2800 Lyngby, Denmark. Phone: +45 4525 3593, Fax: +45 4588 7188, E-mail: pb@iau.dtu.dk
  2. Copenhagen University, Niels Bohr Institute, Department of Geophysics, Juliane Maries Vej 30, DK-2100 Copenhagen Ø., Denmark.
  3. Danish Space Research Institute, Juliane Maries Vej 30, DK-2100 Copenhagen Ø., Denmark.

 

Abstract. The two fluxgate-sensors for the German "CHAMP" satellite have been calibrated in the high precision coilfacility "Magnestrode" of the Technical University of Braunschweig. The aim of this calibration was mainly to verify the linearity and stability of the instruments and to find the variation of the calibration coefficients as a function of temperature. A linear calibration method is used to find the linear coefficients (scale factors, offsets and non-orthogonalities) as well as the inline non-linearities of the instrument. A thin shell calibration exceeding 8 hours and with more than 680 different coil settings shows a long-time stability of the instrument/coil-facility in the order of 0.15 nTrms. This result is obtained in spite of an insufficient adjustment of the ADC's, giving rise to a relatively large non-linearity. Using the thermal chamber of the "Magnestrode" facility, a set of thin shell calibrations was performed, while the temperature of the sensor was changed. The sensor was cooled down to -40°C with dry ice placed above the sensor. The sensor was then passively heated to room temperature and two heat-blankets heated the sensor further up to +30°C. Applying processes from digital signal analysis, the calibration method is extended to resolve the time evolution of the calibration coefficients. In determining the coefficients vs. temperature, the importance of correcting for thermal gradients is addressed. From the result of the thermal analysis the non-orthogonality angles of the magnetometer is found to vary less than 5 arcsec in a span of 70 degrees and the offset stability is better than 0.5 nT. The scale factors of the sensor change with approximately -30 ppm/°C, and the deviation from this linear trend is less than 10 ppm when carefully correcting for the thermal gradient in the sensor.