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Electronic compass design Principles of azimuth measurement and compass operation

Military University of Technology Warsaw, Poland. Faculty of Electronics Institute of Radioelectronics. Electronic compass design Principles of azimuth measurement and compass operation. Author: Jakub Kazubek Tutor: Lt. Col. Piotr Kaniewski , PhD. Earth’s magnetic field.

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Electronic compass design Principles of azimuth measurement and compass operation

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  1. Military University of Technology Warsaw, Poland Faculty of Electronics Institute of Radioelectronics Electronic compass designPrinciples of azimuth measurement and compass operation Author: Jakub Kazubek Tutor: Lt.Col. Piotr Kaniewski, PhD

  2. Earth’s magnetic field • Positions of the magnetic poles do not match the positions of geographic poles • The magnetic poles change their position with time • Earth’s field varies from less than 30µT to over 60µT

  3. The azimuth angle • The direction parallel, to Earth’s surface, component aligns with magnetic S-N direction • The azimuth can be calculated as:

  4. Magnetic field sensorsKMZ51 sensor • The compensation coil allows to compensate the external constant magnetic field • The flipping coil allows to flip internal magnetization vector sense

  5. Sensor offset voltage • Characteristics of the sensor depend on internal magnetization sense (a and b) • The offset voltage does not depend on the internal magnetization direction • The offset voltage depends on supply voltage and can change with time Assuming Earth’s field strength of 15 A/m, supply voltage +5V and maximum temperature differences of 100K: The offset voltage equals: 9mV The voltage caused by the external field is:1,2mV

  6. Offset measurement • Assume a constant external field Hx • Measure Vn voltage • Flip internal magnetization vector • Measure Vp voltage • The offset equals:

  7. Tilt error Transformation between two coordinate systems is needed: Xk Yk Zk =>Xz Yz Zz

  8. Tilt error Tilt error ε depends on: - tilt angle τ - magnetic inclination δ

  9. Tilt correction Horizontal components independent on tilt angle: • Additional elements that have to be measured: • Vertical component Hz – third sensor • Pitch and roll angles – two axis accelerometer

  10. Block diagram

  11. Oscillograms • Voltage across flip coils • Trigger for flip current generator

  12. The compass module

  13. Electronic compass advantages • No mechanical parts • Digital or analogue (PWM) data output • Possibility of Hard Iron Calibration • Possibility of the True North calibration

  14. Project development • Noise elimination • Implementation of the True North algorithm • Gyro correction • Software development

  15. Thank you for your attention

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