Vehicle heading estimation of INS/magnetometer integrated system based on constant hard iron interference calibration

The integrated INS/magnetometer measurement is widely used in low-cost navigation systems. The integration has proven more effective in suppressing the divergence of heading than relying solely on a magnetometer because this is susceptible to local magnetic field interference, reducing heading accuracy. Magnetometers sense the local magnetic field that may be interfered by the nearby ferromagnetic material or strong electric currents. Hence, the magnetometer must be calibrated in the vehicle before use. When a magnetometer is installed near power components (engines, etc.), soft iron interference can be ignored. In the vehicle’s external environment, the time-varying hard iron interference can reach 100 times the strength of the geomagnetic field, meaning that a magnetometer cannot function efficiently because its accuracy is so reduced. Hence, the constant hard magnetic interference inside the vehicle is mainly concerned in this paper. An INS/Magnetometer heading estimation algorithm based on a two-stage Kalman filter is proposed to solve the problem by combining inertial sensor and magnetometer with attitude information. In the first stage filter, the constant hard iron interference is estimated by setting upward standing the three IMU axes. In the second stage filter, the INS/Magnetometer heading estimation is implemented. Finally, the results show that the algorithm improves the accuracy of vehicle heading calculations.

A SIMPLE METHOD FOR THE DETERMINATION OF NITRATE IN ACIDIC SOLUTIONS WITH HIGH IRON CONTENT BASED ON THE TRADITIONAL CADMIUM REDUCTION TECHNIQUE

A simple and unexpensive method based on traditional cadmium column technique is proposed for determination of nitrate in acidic aqueous mixtures with high iron load. Solutions are alkalinized and centrifuged, subsequently the supernatant is withdrawn for nitrate analysis. By this procedure two effects are accomplished, on the one hand, pH is adjusted to a suitable value and, on the other hand, iron interference is removed by precipitation. The obtained mixture is passed through a copperized cadmium column to reduce nitrate to nitrite which is quantified spectrophometrically. This method is suitable to measure nitrate concentrations even lower than the maximum accepted limit, in artificial solution.

Twelve-Position Calibrating Method without North Using for Three-Axis Magnetic Sensor

In allusion to the compensation of environmental magnetic field for using three-axis magnetic sensor, a twelve-position calibrating method without north is designed. The equations of three-axis bias, scale factor error and install alignment error are deduced in the proposed method which is totally based on the magnetic field of up direction. According to the effect of hard iron and soft iron is equaled to the variation of three-axis bias, scale factor error and install alignment error, comparison experiments are completed in natural conditions and in conditions that the effect of hard iron and soft iron is artificially imposed. The experiment shows that this method can solve the compensation of hard iron and soft iron interference effectively for the application of up direction tumbling test.