Question about NULL_CNFG for IMU device

Question

I have some questions about NULL_CNFG(Continous bias estimation) for IMU devices. 
 #1, what's the function of NULL_CNFG? If you have some material to explain this function, please let me know. 
 #2, About ADIS16480, Table3 says mention &ldquo;NULL_CNFG&rdquo; stall times, but I can&rsquo;t find &ldquo;NULL_CNFG" on the register of USE REGISTERS map. Is it possible to use NULL_CFG on ADIS16480? (It looks like ADIS16489 has the NULL_CFG register on the user reg map) 
 https://www.analog.com/media/en/technical-documentation/data-sheets/ADIS16480.pdf 
 
 Best, 
 Tarzan2

ADIApproved · Accepted Answer

Hello Tarzan2, 
 I have a correction from what I previously wrote. The ADIS16480 has auto-nulling function, and it's in the GLOB_CMD register labeled as a Tare command. "NULL_CFG" in Table 3 of the datasheet is the amount of time required to complete this command. 
 The goal of this command is the orient the IMUs x/y/z axes to East/North/Up (ENU) by using the reference transformation matrix as described on Page 30 of the datasheet. After the tare function, assuming the local navigation frame is selected, the IMU will report 0 deg pitch, and 0 deg roll, and the accelerometers will read x=0g, y=0g, and z=1g, even though the IMU wasn't necessarily laying flat during execution of the Tare command. If you want to see what the accelerometers read relative to the orientation of the IMU, set the Body Frame bit in the EKF_CONFIG register to 1. 
 I hope this helps, and I apologize for the confusion. 
 -Paul Kern)

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Question about NULL_CNFG for IMU device