Prepared by: Brian Moss Dept. of Mechanical and Aerospace Engineering Utah State University

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Fluxgate Magnetometer Sensors Prepared by: Brian Moss Dept. of Mechanical and Aerospace Engineering Utah State University 3/2/2009

2. Outline • Reference list • To probe further • Major applications • Basic working principle illustrated • A typical sample configuration in application • Digital v Analog • Major specifications • Limitations • Other options to consider ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • www.geo.ucalgary.ca/~wu/Goph547/MagneticMeasurement.pdf • http://www3.imperial.ac.uk/spat/research/areas/space_magnetometer_laboratory • http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THG-4G4MMHY-1&_user=464852&_rdoc • http://www.igpp.ucla.edu/public/THEMIS/SCI/Pubs/2008_Refereed/auster_fulltext.pdf • http://www.iop.org/EJ/article/0022-3735/12/4/001/jev12i4p241.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. Reference List • http://www-ssc.igpp.ucla.edu/st5/design.html • http://en.wikipedia.org/wiki/Magnetometer • http://129.128.241.207/carismaweb/content/view/72/1/ • http://cse.ssl.berkeley.edu/SegwayEd/lessons/exploring_magnetism/background/guide_chapter5.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major applications • Fluxgate Magnetometers sense the intensity and orientation of magnetic fields • Originally designed to detect submarines in WWII • Now measure fluxuations in earth’s magnetic field due to solar winds and tectonic plate shifts • Many space applications to detect planet’s and moon’s gravitational fields and their orientation • Prospecting for minerals and artifacts underneath earth’s surface • Used extensively in directional drilling ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Basic Working Principles • 2 highly ferromagnetic cores are placed in close proximity to each other symmetrically opposed • Each core is wound with a primary coil, the primary windings are reversed of each other • An alternating current is applied to the primary windings producing a variable mag field in both cores • The induced mag fields in the cores are equal and opposite cancelling each other out when no external mag field is present ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Basic Working Principles ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Basic Working Principles • When an external mag field is present the core generating a field opposite to its direction will come out of saturation sooner while the core in line with its direction will come out of saturation later • During this time the fields do not cancel out and there is a net change in flux • This change in flux induces a voltage across the secondary windings which can be measured ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Basic Working Principles ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Basic Working Principles • It is important that the two cores reach magnetic saturation so that the differences in the fields can be readily known, the greater the susceptibility of the cores the less current needed. • Often to increase sensitivity the core is one ring which can be thought of as two halves still working in opposite directions as the rod cores ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Basic Working Principles ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Typical Fluxgate Magnetometer Configurations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Typical Fluxgate Magnetometer Configurations • The tuning capacitor is often necessary to ensure that the induced voltage from the sense winding is twice the frequency of the input signal • The synchronous detector compares the phase of the reference block input signal to the received ‘2f’ signal from the sense winding to determine the sign of the measured field • The analog signal is most often converted to digital so that the results can be displayed on an LCD • The sensed voltage is fed back and converted to current that is adequate to cancel out the external field ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Typical Fluxgate Magnetometer Configurations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Typical Fluxgate Magnetometer Configurations • In digital fluxgate magnetometers the analog signal is converted to digital before integration, phase comparison, and display. It is then converted back to analog through low-pass filters and amplifiers to supply the feedback voltage that is converted to current to cancel out the external field. • To do this digitally the instruments employ Field-programmable gate arrays (FPGA) or Application-specific integrated circuits (ASIC) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Digital v Analog • Digital fluxgate magnetometers are generally lighter, consume less power, show less drift, and better resolution • Digital fluxgate magnetometers however introduce DAC non-linearity into the feedback signal influencing non-linearity into the whole sensor • Analog fluxgate magnetometers generally can operate over a greater bandwidth ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Major Specifications ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Limitations • All fluxgate magnetometers are relative vector instruments that must be calibrated in known magnetic fields and oriented correctly to gain accurate results ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Limitations • Ability to maintain consistent knowledge and stability of sensor axes • The “susceptibility” of the cores to magnetic saturation • Severe temperature changes result in large drifts • All fluxgate magnetometer’s are considered most reliable between 0 to 60 Hz ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Manufacturers and Cost • Applied Physics Systems • ASC Scientific • Bartington Instruments • Billingsley Aerospace • MEDA • THEMIS • Stefan Mayer Instruments • Watson Industries ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Other Options to Consider and Explore • Hall Effect Sensors – often a reliable cheaper substitute in many lab applications • Proton Precession Magnetometer – very accurate sensor that senses the alignment of protons due to a magnetic field, they are less reliant on stable and precise orientation, however they are considerably more expensive ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators