Design Of A Compass Based On TMR Sensor

Electronic compass is a directional navigation equipment to achieve the measurementof azimuth through using the geomagnetic field. Electronic compass is provided with theadvantages of small volume, flexible operation, high accuracy and low power, which haswide range of applications in the aerospace, marine surveying, navigation, aircraft controland many other fields, and has major impacts in the development of national economy andthe military, so in recent years, it has been a hot topic at home and abroad.Currently, the geomagnetic detection of electronic compass uses the sensors of HALL,AMR and GMR effects or flux gate technology, which possess the shortcomings of lowsensitivity, poor linearity, complex circuit and great volume and so on. As thefourth-generation magnetoresistive sensor, to some extent, TMR sensor makes up for thelacks of the above effects with the features of high sensitivity, good linearity and widedynamic ranges and so on. The design is the application of TMR that is in electroniccompass against this background.The measurement principle of common reluctance electronic compass is first discussedin the paper. On this basis, the effects and the advantages of the TMR sensor used isrespectively described and analyzed. Then, the software and hardware design, dataprocessing and algorithms to compensate, system calibration and other contents arediscussed in the electronic compass system design.In the hardware design, the sensor and conditioning circuit, system control, datatransmission and other circuit unit in the compass system are focused discussed in thedevice selection and circuit design according to the performance goals and indicatorparameters of the system; In the software design, the data acquisition control of ADC, theerror data processing and compensation, the azimuth solver, the data transmission and othercontents are designed respectively according to the system function; Finally, the systemprototyping is finished. For data processing and algorithm compensating, first of all, the compass systemcalibration experiment was carried out to obtain the compensation parameters. Then thecommon error sources of compass system are analyzed. In view of the main error source ofmanufacture, installation, compass deviation, and on the basis of comparing a variety ofcommon compensation methods, the ellipsoid or ellipse fitting and the least squaresalgorithm are selected and adopted for data correction and error compensation.In the aspect of experiment, the sensor performance of the three magnetic resistanceeffect with AMR, GMR, TMR are tested, the experimental results show that: the linearity ofthe TMR sensor is good, up to0.64%, and the measurement sensitivity is7.59mv/v/Gs,which is obviously several times or even one order of magnitude higher than that of AMRsensor (0.43mV/V/Gs) and GMR sensor (2.83mV/V/Gs). In the azimuth testing experiment,the test results through ellipsoid fitting, the parameter is acquired, which the sensor andaccelerometer can be corrected; Through ellipse fitting, the magnetic interference errorparameters are obtained, and the azimuth accuracy is improved up to0.69°; and throughleast square method, the azimuth eventually reach to0.435°.The project achieves the prototype of principle by studying, and the experimentalresults verify the feasibility of the TMR effect in electronic compass, which has significanceto study further a new generation of tunneling magnetoresistive electronic compass.