Specification of Sensor class

1. Overview

1. Functions

The Sensor class is a base class to provide common features for sensors.
This class adds the following noises and output limits.
- Constant offset noise
- Normal random noise
- Random Walk noise
- Scale factor noise and cross-talk between axes

2. Related files

Main file: sensor_base.cpp, .hpp
Used Libraries: vector.hpp, matrix.hpp, normal_randomization.hpp, random_walk.hpp

3. How to use

Inherit this class by your sensor class.
The GyroSensor and Magnetometer in S2E_CORE are useful as usage examples.

2. Explanation of Algorithm

1. Constructor

1. overview

Users can set sensor noise parameters by using the Constructor.

2. inputs

scale_factor: Scale factor matrix to express scale factor noise and cross-talk
Range related parameters
- range_to_const_c: The output value cannot over this value
- range_to_zero_c: The output is set as zero when the true value is larger than this value.
- This feature is optional. If you don't want to use the value, please set this huge value.
- range_to_zero_c should be larger than range_to_const_c.
bias_noise_c: Constant offset noise
normal_random_standard_deviation_c: Standard deviation for normal random noise
Random Walk noise parameters
- random_walk_step_width_s: Step width for Random Walk propagation (unit: sec)
  - It should be the same as the update frequency of the sensor.
- random_walk_standard_deviation_c: Standard deviation for Random Walk
- random_walk_limit_c: Soft limit of Random Walk
Note: The number of elements for all parameters can be set by using the template feature.
Note: All parameters are defined in the component frame.
Note: Normally, the unit of the parameters is the same as the unit of true value. Users also can change the unit by using the scale factor matrix.

3. algorithm

The values of the range_to_const_c and range_to_zero_c are checked here with the RangeCheck function.

4. note

N/A

2. Measure

1. overview

This function adds all noises, and the output is clipped by the Clip function not to over the ranges.

2. inputs and outputs

input: True value on the component frame
output: Measured value on the component frame

3. algorithm

N/A

4. note

N/A

3. Results of verifications

We verified the Sensor class with the following parameters.
Default parameters
- scale_factor = Unit matrix
- range_to_const_c = 5
- range_to_zero_c = 10
- bias_noise_c = 0.0
- normal_random_standard_deviation_c = 0.0
- random_walk_step_width_s= 0.1 sec
- random_walk_standard_deviation_c = 0.0
- random_walk_limit_c = 0.0
- input value: 0.0
Case 1: bias_noise_c = 1.0, others = default
- The bottom figure shows the result of the output data.
- We verified the constant offset noise calculation is correct according to the data.
Result of constant offset noise (bias_noise_c = 1.0).
Case 2: normal_random_standard_deviation_c = 1.0, others = default
- The simulation time is 1000sec, and the log output period is 0.1sec.
- The bottom figure shows the result of the output data.
- The calculated average and standard deviation from the output data are shown as follows.
  - Average = 0.012
  - Standard Deviation = 1.000
- We verified the normal random noise calculation is correct according to the data.
Result of normal random noise (normal_random_standard_deviation_c = 1.0).
Case 3: random_walk_standard_deviation_c = 0.3, random_walk_limit_c = 0.05, others = default
- The simulation time is 200sec, and the log output period is 0.5sec.
- The bottom figure shows the result of the output data.
- The output data randomly varies inside the limit value.
  - Note: The limit is not hard.
- We verified the normal random noise calculation is correct according to the data.
Result of Random Walk noise (random_walk_standard_deviation_c = 0.3, random_walk_limit_c = 0.05).

4. References

N/A