Inertial sensor models#

Inertial sensor models: white noise, a drifting bias and a sample rate.

A Sensor measures the acceleration along one axis as a + bias + noise. The bias follows a random walk. These are the standard first-order error terms of an accelerometer (Allan-variance noise terms: velocity random walk and bias instability); the two presets differ in exactly the way that matters for fusion: a MEMS accelerometer is fast and drifts, a cold-atom interferometer is slow and almost drift-free.

The preset values are illustrative assumptions, not measurements of any product. The atom-interferometer noise is derived from the quantum limit (quantum_mind.sensing.atom_interferometer_sensitivity()) for the atom number and interrogation time you pass; its bias walk is an assumption. Set every number for the sensors you care about.

Classes

Sensor

One accelerometer.

Functions

mems_accelerometer

A MEMS accelerometer: fast, noisy, with a drifting bias (illustrative values).

atom_interferometer_accelerometer

A cold-atom interferometer accelerometer: slow, very sensitive, almost drift-free (illustrative values).
class Sensor(name, rate_hz, noise_std, bias_walk, bias_std0)[source]#

Bases: object

One accelerometer.

Variables:

  • name (str)

  • rate_hz (float) – Samples per second.

  • noise_std (float) – Standard deviation of the white noise of one sample, in m/s^2.

  • bias_walk (float) – Bias random-walk density in (m/s^2)/sqrt(s).

  • bias_std0 (float) – Standard deviation of the initial bias in m/s^2.

Parameters:
mems_accelerometer(rate_hz=100.0, noise_density_ug=100.0, bias_walk=0.0002, bias_std0=0.02)[source]#

A MEMS accelerometer: fast, noisy, with a drifting bias (illustrative values).

Parameters:

  • rate_hz (float, optional) – Output rate.

  • noise_density_ug (float, optional) – Velocity random walk expressed as an acceleration noise density in micro-g per root hertz.

  • bias_walk (float, optional) – Bias random-walk density in (m/s^2)/sqrt(s).

  • bias_std0 (float, optional) – Initial bias spread in m/s^2.

Returns:

Sensor

atom_interferometer_accelerometer(n_atoms=1000000.0, interrogation_time=0.1, cycle_time=1.0, contrast=0.5, bias_walk=1e-08, bias_std0=1e-06)[source]#

A cold-atom interferometer accelerometer: slow, very sensitive, almost drift-free (illustrative values).

The per-shot noise comes from the standard quantum limit for n_atoms and interrogation_time; the rate is one sample per cycle_time (atom preparation and detection dominate it). The bias walk and initial bias are assumptions.

Returns:

Sensor