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Use of Active Heading Stabilization (AHS) in MTi

Active Heading Stability (AHS) is an algorithm that estimates the gyro bias in the horizontal plane, enabling a better heading tracking performance. In different products, AHS is activated in different situations.

 

It is advised to read the introduction to AHS on xsens.com/ahs

 

MTi 1-series, 10-series and MTi 100-series with VRU_general filter profile

By default, AHS is off, also in the VRU_general filter profile. Activate it by setting the flag in SetOptionFlags (see documentation.xsens.com/mt_low-level_communication_protocol). AHS estimates the gyro bias when there is a prolonged period of undisturbed magnetic field. The statistics on this is the major function of the algorithm. The best performance is most likely to be reached when the MTi is not moving with engines off. If the MTi is warmed up sufficiently (>10 minutes), the estimated gyro bias accuracy will degrade only slowly so that a gyro bias estimation is required only several times per hour. 

MTi 1-series, 10-series and MTi 100-series with filter profiles that use magnetic field as a reference

By default, AHS is off. Activate it by setting the flag in SetOptionFlags (see documentation.xsens.com/mt_low-level_communication_protocol). When AHS is enabled, this feature will override magnetic reference tracking. This means that the accelerometer parameters in e.g. the dynamic filter profile are preserved, but that AHS is used for heading tracking. AHS estimates the gyro bias when there is a prolonged period of undisturbed magnetic field. The statistics on this is the major function of the algorithm. The best performance is most likely to be reached when the MTi is not moving with engines off. If the MTi is warmed up sufficiently (>10 minutes), the estimated gyro bias accuracy will degrade only slowly so that a gyro bias estimation is required only several times per hour. 

Heading (tracking) information in MTi 1-, 10-, 100-series

VRU_general

Filter profiles with mag reference
Gyroscope integration (heading tracking) Yes Yes
Magnetic reference (heading reference)

No

AHS off: Yes

AHS on: No

AHS (heading tracking)

AHS off: No

AHS on: Yes

AHS off: No

AHS on: Yes

 

 

MTi-G-700/710

By default, AHS is off. Activate it by setting the flag in SetOptionFlags (see documentation.xsens.com/mt_low-level_communication_protocol). When AHS is enabled, this feature will override magnetic reference tracking (for the MTi-G-700/710, this is the GeneralMag filter profile). However, heading reference with GNSS/accelerometer comparison still functions when there is GNSS visibility. When there is movement, heading from GNSS/accelerometer comparison is the most accurate heading source of the MTi-G-700/710. AHS estimates the gyro bias when there is a prolonged period of undisturbed magnetic field. The statistics on this is the major function of the algorithm. The best performance is most likely to be reached when the MTi is not moving with engines off. If the MTi is warmed up sufficiently (>10 minutes), the estimated gyro bias accuracy based on AHS will degrade only slowly so that a gyro bias estimation is required only several times per hour. However in the MTi-G-700/710, gyro bias is also estimated using the GNSS/accelerometer comparison next to AHS. This makes that the gyro bias can actually always be estimated and that heading drift in the MTi-G-700/710 is minimal.

 

Heading (tracking) information in MTi-G-700/710 Filter profiles with mag reference Filter profiles without mag reference Automotive filter profiles
Gyroscope integration (heading tracking) Yes Yes Yes
Magnetic reference (heading reference)

AHS off: Yes

AHS on: No

No

No 
GNSS/accelerometer comparison (heading reference) Yes, when accelerating or making turns when there is a GNSS fix Yes, when accelerating or making turns when there is a GNSS fix Yes, when accelerating or making turns when there is a GNSS fix
Holonomic constraints (heading tracking, GNSS course = heading) No  No Yes 
AHS (heading tracking)

AHS off: No

AHS on: Yes

AHS off: No

AHS on: Yes 

AHS: No

AHS: Yes

 

 

 

 

 

 

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