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--- resources:eval:user-guides:inertial-mems:imu-overview [21 Jul 2021 01:18] – [Angular Random Walk (ARW)] Chas Frick
+++ resources:eval:user-guides:inertial-mems:imu-overview [31 Aug 2021 22:00] (current) – [Linear Acceleration Effect (Linear-g), Linear Acceleration Effect on Bias, Linear-g Rejection (Linear-g Sensitivity)] Chas Frick
@@ Line 1: / Line 1: @@
 ====== ADI MEMS IMUs Glossary: Performance Characteristics, Measurement Setups and Applications ======
 This page is intended to introduce and discuss common characteristics of MEMS IMUs, how to measure those performance metrics and finally some applications where those metrics matter.
+====== Bias Repeatability ======
+Measured in °/hour.
 ====== Bias Error ======
-Offset error in MEMs output on a particular axis. Fixed error typically.
+Offset error in MEMs output on a particular axis. Fixed error typically. Measured in °/hour.
 ====== Sensitivity Error ======
@@ Line 14: / Line 17: @@
 This can be thought of as the sensor resolution in an "ideal case." It is also found as the minimum of the AVAR plot.
-====== Angular Random Walk (ARW) ======
+====== Angle Random Walk (ARW) ======
-Applies to gyroscopes. It is the "close-in" (small τ) on the AVAR curve and is noise that comes from the quantization process. Taken at Τ = 1 second.
+Measured in °/hour/√Hz or °/√hour.
-====== (Angular) Rate Random Walk (ARRW) ======
+Applies to gyroscopes. It is the "close-in" (small τ) on the AVAR curve and is noise that comes from the quantization process. Taken at Τ = 1 second. In order to calculate the ARW, take the value of the square-root of the AllanVariance and divide by 60 [iMAR].
+For an example consider the ADIS16153, with datasheet here: [[adi>media/en/technical-documentation/data-sheets/ADIS16135.pdf#Page=08]]. The graph of the AllanVariance is this:
+{{ :resources:eval:user-guides:inertial-mems:2021-07-22_09_29_19-adis16135_rev._f_.png |}}
+Additional notes: [[http://home.engineering.iastate.edu/~shermanp/AERE432/lectures/Rate%20Gyros/Rate%20Gyro%20Explanations.pdf|iMAR Research Background]]
+====== Rate Random Walk (ARRW) ======
 Applies to gyroscopes and is the "far out" (large Τ) on the Allan Variance (AVAR) curve.
 This quantity represents long-term stability of the sensor measurement.
@@ Line 29: / Line 43: @@
 Can be approximated with the formula: ND ≅ ARW/60* √2
-====== Linear Acceleration Effect (Linear-g) ======
-Measured in degrees/sec/g.
 ====== Vibration Rectification Error (VRE) ======
 Measured in degrees/sec/g².
+====== Cross-Axis Sensitivity ======
+Unintended effect where rotation/acceleration from one axis is detected on another axis.
+Can be calculated from axis to axis misalignment error for accels/gyros: sin(axis to axis misalignment) in %
+Example: For the ADIS16448, the accel axis to axis misalignment is 0.2 degrees. Therefore Cross-axis sensitivity accel is sin(0.2) = 0.197%. Gyro is sin(0.05) = 0.09%. Magnetometer: sin(0.25) = 0.247%
+====== Linear Acceleration Effect (Linear-g), Linear Acceleration Effect on Bias, Linear-g Rejection (Linear-g Sensitivity) ======
+Unintended effect where linear acceleration is detected as rotation. Measured in degrees/sec/g.
+====== Vibration Rejection (Gyros) ======
+A combination of Linear-g and Vibration Rectification (VRE) specs.
+Vibration response of a gyro = Linear-g X-Axis Acceleration + (VRE X-Axis Acceleration)^2
+====== Additional Resources! ======
+* Information on Allan Variance for Gyros: http://www.alexandertrusov.com/uploads/pdf/2011-UCI-trusov-whitepaper-noise.pdf

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