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Bias repeatability of gyroscopes

Every MTi is factory-calibrated at Xsens. When an MTi does not meet the quality requirements, it will be rejected. This happens for example, when the bias is too large or when the gain is not in the expected range. These units may still be accurate, but we reject these MTi's to deliver only the highest quality to customers. 

Bias repeatability (or turn-on to turn-on bias stability) however is a parameter that cannot be calibrated. Every time when the MTi is powered, the initial bias of the gyroscopes and accelerometers may be a little bit different. Possible causes are the relaxation of the mass in the spring system, temperature distribution that is not yet homogeneous during the warm-up phase etc. 

This bias repeatability is +/- 0.5 º/s within one year. Luckily, this offset value will be estimated by the sensor fusion algorithm when the MTi is used. There are several ways in which the MTi estimates the bias:

  • For roll and pitch the gravity is used to estimate the gyro bias. A manual estimation (NoRotation Update) can also be achieved by choosing the Gyro Bias estimation from the MT Settings menu in MT Manager or by using the command SetNoRotation. Note that gyro bias may change during the warm up period. It is therefore important to properly warm up the MTi before applying the NoRotation Update (at least 5 minutes, preferably 10 minutes or more). 

  • For heading of the MTi-20, MTi-200, MTi-30 or MTi-300, the bias estimation depends on the filter profile:
    • General: magnetometer or NoRotation update
    • High_mag_dep: magnetometer or NoRotation update
    • Dynamic: magnetometer or NoRotation update
    • Low_mag_dep: magnetometer or NoRotation update
    • VRU_general: AHS or NoRotation update

  • For heading of the MTi-G-700, the bias estimation depends on the filter profile:
    • General: NoRotation update and accelerometer/GPS comparison
    • GeneralNoBaro: NoRotation update and accelerometer/GPS comparison
    • GeneralMag: magnetometer, NoRotation update and accelerometer/GPS comparison
    • Automotive: NoRotation update, accelerometer/GPS comparison and holonomic constraints
    • AutomotiveUrbanCanyon: NoRotation update, accelerometer/GPS comparison and holonomic constraints


 

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