Does anyone have any opinions on rate tables for calibration of the mems gyro/accelerometers on Shimmer? Has anyone worked with IXMotion or Aerotech? Any information on the best product for this work? Do you recommend the use of a strobe to accurately measure the period of rotation? Is a single axis rate table sufficient, or do you introduce too much error calibrating for each axis separately when you go to position the device?
-james -----Original Message----- From: Jonathan Lin [mailto:[email protected]] Sent: Friday, August 12, 2011 5:52 PM To: [email protected] Subject: [Shimmer-users] Accel/gyro calibration questions Hi everyone, I've been trying to figure out accelerometer and gyroscope calibrations, and am a bit confused at what I've been reading. I have a set of SHIMMER2R with gyroscope board, so the MEMS that are onboard should be the accelerometer MMA7361L and the gyroscope IDG500, right? A few questions: 1) I was reading though the Shimmer_AccelCalibration document, and the document cites the datasheet for the MMA7260Q, which is different than the ones on the SHIMMER2R. Does the scaling values cited in this document, particularly 744 (for sensitivity) and 372 (conversion to g) still apply to the MMA7361? 2) The equation provided in Shimmer_AccelCalibration, to convert ADC units to units of g, is: [1] sensitivity_error * (measured_value - calculated_midpoint) / 372 In an ideal case, this equation would be (measured_value - 2048)/372 However, looking at Section 9.1 of Shimmer User Manual 2Rc, for 1.5g, my ideal equation is [2] (measured_value - 2048) / 993 Evidently, these two equations would return different values. Which equation should I be following? I was using the eq'n [2], which appears to be correct, and just assuming my system is ideal, but now would like to account for the calibration errors in my devices. Should I just take eq'n [1] and replace 372 with 993? 3) Looking at the tables in the MMA7361 and MMA7260, the sensitivity values are different than that reported in the table in Section 9.1. I can see that the Section 9.1 table is just the reported table rescaled from 3.3V to 3.0V. Can we assume that the SHIMMER2R is able to provide a constant 3.0V? Though, I suppose the calibration techniques outlined here would correct for the voltage scaling. 4) Lastly, I was wondering if there are documented methods on gyroscope calibration? A search online tells me that the best way to do this is to find a turntable and basically do the same +g/-g procedure as is with the accelerometer. Are there other methodologies out there, or should I just focus on obtaining a turntable or a motor of some sort? Thanks in advance. -Jonathan _______________________________________________ Shimmer-users mailing list [email protected] https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
