Disclaimer: AHS is still in beta for MTi-G-700/710 and MTi-7. Although the feature is available, it was not designed or extensively tested for these devices.
Active Heading Stabilization (AHS) is a software component within the sensor fusion engine designed to give a low-drift unreferenced (not North-referenced) yaw solution even in a disturbed magnetic environment. It is aimed to tackle magnetic distortions that do not move with the sensor, i.e. temporary or spatial distortions. The magnetic norm can be used to identify these magnetic distortions.
AHS is available in all products and filter profiles. Therefore, the user can get a stable yaw solution even with a VRU product. When AHS is applied to a filter profile that uses the magnetic field as a reference, the magnetic field will no longer be used as a reference. The yaw output will be referenced with respect to startup heading orientation, instead of North-referenced. Upon initialization of the sensor, the yaw estimate will therefore be 0 degrees. With AHS enabled, the drift in yaw can be as low as 1 degree after 60 minutes for the MTi 100-series and 3 degrees after 60 minutes for the MTi 10-series. When enabling AHS, there are several considerations to keep in mind. First, during initialization of the sensor, AHS requires the MTi to be motionless for a short period of time. Depending on your configuration, this initialization process may take between 10 and 30 seconds.
When the application expects that either the MTi or the magnetic field rotates very slowly, it is recommended to not enable AHS.
How to enable AHS
AHS is off by default from firmware version 1.4.12, also when using the VRU_general filter profile. The user can enable AHS through Low Level Communication, XDA or simply using MT Manager:
|Low Level Communication||
Configure the device at Low Level Communication. See SetOptionFlags section in MT Low Level Communication Protocol Documentation.
Use the setDeviceOptionFlags function. Refer to the XDA library (found in your MT SDK Documentation folder) for more information.
This method is not available for GNSS/INS devices (MTi-7 or MTi-G-710).