# US 10,119,819 B2 · Method and system for compensating for soft iron magnetic disturbances in a heading reference system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,119,819 B2 - Document ID: US10119819B2 - Status: Granted - Kind: B2 - Application number: 15/488,098 - Filed: 2017-04-14 - Published: 2017-08-03 - Granted: 2018-11-06 - Earliest claimed: 2012-06-21 - Assignees: Innovative Solutions & Support, Inc. - Applicants: Innovative Solutions & Support, Inc. - Inventors: Shahram Askarpour - Web page: https://patentgrep.com/patent/US10119819B2 ## CPC - G01C 17/38: Testing, calibrating, or compensating of compasses - G01C 19/36: with north-seeking action by magnetic means, e.g. gyromagnetic compasses - G01C 21/1654: {with electromagnetic compass} - G01C 23/00: Combined instruments indicating more than one navigational value, e.g. for aircraft; Combined measuring devices for measuring two or more variables of movement, e.g. distance, speed or acceleration - G01C 23/005: {Flight directors (indicating arrangements specially adapted for rotary gyroscopes G01C19/32)} - G01C 25/005: {initial alignment, calibration or starting-up of inertial devices} - G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S) ## Abstract A method and system for compensating for significant soft iron magnetic disturbances in a heading reference system, such as an aircraft heading reference system, such as an integrated standby unit; or a vehicle inertial system, provides a heading correction signal to the heading reference system when a detected difference in value between a gyro heading relative to magnetic north and a magnetometer reading during a defined measurement period exceeds a predetermined acceptable threshold value of change, such as one based on the expected gyro drift over that period. Upon receipt of the heading correction signal, the gyro heading is adjusted to maintain an accurate heading relative to true magnetic north. If this threshold value is not exceeded, then the magnetometer reading is used for the heading value. This method is iteratively repeated in order to continually maintain an accurate heading and may be employed for each heading measurement axis. ## Claims ### Claim 1 A system for compensating for soft iron magnetic disturbances in a heading reference system, the system comprising: a magnetometer; a gyroscope; and a processor configured to: receive a first measurement value associated with the magnetometer; receive a second measurement value associated with the gyroscope; determine a first rate of change for magnetometer readings over a time period using the first measurement value and one or more magnetometer measurement values received prior to the first measurement value; determine a second rate of change for gyroscope readings over the time period using the second measurement value; determine a differential rate of change by subtracting the first rate of change from the second rate of change; and compensate for soft iron effects on the magnetometer based on a gyroscope reading, if the magnitude of the differential rate of change is greater than a maximum expected drift for the gyroscope. ### Claim 2 (depends on 1) The system of claim 1, wherein the processor is configured to calculate an estimate of attitude and heading. ### Claim 3 (depends on 2) The system of claim 2, wherein the estimate of attitude and heading is calculated using a magnetometer reading, if the magnitude of the differential rate of change is less than a maximum expected drift for the gyroscope. ### Claim 4 (depends on 2) The system of claim 2, wherein the estimate of attitude and heading is calculated using a gyroscope reading and a prior heading, if the magnitude of the differential rate of change is greater than a maximum expected drift for the gyroscope. ### Claim 5 (depends on 1) The system of claim 1, wherein the processor is configured to compensate for gyroscope sensor drift using a magnetometer reading, if the magnitude of the differential rate of change is less than the maximum expected drift for the gyroscope. ### Claim 6 (depends on 5) The system of claim 5, wherein compensating for gyroscope sensor drift includes applying an extended Kalman filter to gyroscope and magnetometer readings. ### Claim 7 (depends on 1) The system of claim 1, wherein the processor is configured to blend magnetometer and gyroscope readings based on their corresponding error covariances. ### Claim 8 A method for compensating for soft iron magnetic disturbances in a heading reference system, the method comprising the steps of: receiving a first measurement value associated with a magnetometer; receiving a second measurement value associated with a gyroscope; determining a first rate of change for magnetometer readings over a time period using the first measurement value and one or more magnetometer measurement values received prior to the first measurement value; determining a second rate of change for gyroscope readings over the time period using the second measurement value; determining a differential rate of change by subtracting the first rate of change from the second rate of change; and compensating for soft iron effects on the magnetometer based on a gyroscope reading, if the magnitude of the differential rate of change is greater than a maximum expected drift for the gyroscope. ### Claim 9 (depends on 8) The method of claim 8, further comprising calculating an estimate of attitude and heading. ### Claim 10 (depends on 9) The method of claim 9, wherein the estimate of attitude and heading is calculated using a magnetometer reading, if the magnitude of the differential rate of change is less than a maximum expected drift for the gyroscope. ### Claim 11 (depends on 9) The method of claim 9, wherein the estimate of attitude and heading is calculated using a gyroscope reading and a prior heading, if the magnitude of the differential rate of change is greater than a maximum expected drift for the gyroscope. ### Claim 12 (depends on 8) The method of claim 8, further comprising compensating for gyroscope sensor drift using a magnetometer reading, if the magnitude of the differential rate of change is less than the maximum expected drift for the gyroscope. ### Claim 13 (depends on 12) The method of claim 12, wherein compensating for gyroscope sensor drift includes applying an extended Kalman filter to gyroscope and magnetometer readings. ### Claim 14 (depends on 8) The method of claim 8, further comprising blending magnetometer and gyroscope readings based on their corresponding error covariances. ### Claim 15 A system for compensating for soft iron magnetic disturbances in a heading reference system, the system comprising: a magnetometer; a gyroscope; and a processor configured to: receive a first measurement value associated with the magnetometer; receive a second measurement value associated with the gyroscope; determine a first rate of change for magnetometer readings over a time period using the first measurement value and one or more magnetometer measurement values received prior to the first measurement value; determine a second rate of change for gyroscope readings over the time period using the second measurement value; determine a differential rate of change by subtracting the first rate of change from the second rate of change; calculate an estimate of attitude and heading using a magnetometer reading, if the magnitude of the differential rate of change is less than a maximum expected drift for the gyroscope; and calculate an estimate of attitude and heading using a gyroscope reading and a prior heading, if the magnitude of the differential rate of change is greater than the maximum expected drift for the gyroscope. ### Claim 16 (depends on 15) The system of claim 15, wherein the processor is configured to: compensate for soft iron effects on the magnetometer using a gyroscope reading, if the magnitude of the differential rate of change is greater than the maximum expected drift for the gyroscope. ### Claim 17 (depends on 15) The system of claim 15, wherein the processor is configured to: compensate for gyroscope sensor drift using a magnetometer reading, if the magnitude of the differential rate of change is less than the maximum expected drift for the gyroscope. ### Claim 18 (depends on 17) The system of claim 17, wherein compensating for gyroscope sensor drift includes applying an extended Kalman filter to gyroscope and magnetometer readings. ### Claim 19 A method for compensating for soft iron magnetic disturbances in a heading reference system, the method comprising the steps of: receiving a first measurement value associated with a magnetometer; receiving a second measurement value associated with a gyroscope; determining a first rate of change for magnetometer readings over a time period using the first measurement value and one or more magnetometer measurement values received prior to the first measurement value; determining a second rate of change for gyroscope readings over the time period using the second measurement value; determining a differential rate of change by subtracting the first rate of change from the second rate of change; calculating an estimate of attitude and heading using a magnetometer reading, if the magnitude of the differential rate of change is less than a maximum expected drift for the gyroscope; and calculating an estimate of attitude and heading using a gyroscope reading and a prior heading, if the magnitude of the differential rate of change is greater than the maximum expected drift for the gyroscope. ### Claim 20 (depends on 19) The method of claim 19, further comprising: compensating for soft iron effects on the magnetometer using a gyroscope reading, if the magnitude of the differential rate of change is greater than the maximum expected drift for the gyroscope. ### Claim 21 (depends on 19) The method of claim 19, further comprising: compensating for gyroscope sensor drift using a magnetometer reading, if the magnitude of the differential rate of change is less than the maximum expected drift for the gyroscope. ### Claim 22 (depends on 21) The method of claim 21, wherein compensating for gyroscope sensor drift includes applying an extended Kalman filter to gyroscope and magnetometer readings.