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# 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. Measured in °/hour.

# Sensitivity Error

An error in the gain of the response. Non-uniformity that affects measurement output.

# Allan Variance (AVAR)

A plot of noise versus averaging time.

# In-run Bias Stability (IRBS)

This can be thought of as the sensor resolution in an “ideal case.” It is also found as the minimum of the AVAR plot.

# Angle Random Walk (ARW)

Measured in °/hour/√Hz or °/√hour.

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: media/en/technical-documentation/data-sheets/ADIS16135.pdf#Page=08. The graph of the AllanVariance is this:

# 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.

# Velocity Random Walk (VRW)

Similar to the angular random walk (ARW) for gyroscopes. Noise from quantization of the axes.

# Noise Density

Similar to amplifier noise density. RMS noise per unit of BW. 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

# Linear-g Rejection (Linear-g Sensitivity)

Unintended effect where linear acceleration is detected as rotation