# Calibrate Sensors that are sensitive to changes in the operating environment produce inappropriate output values due to factors, such as temperature variations, mechanical wear, or shift in the operating range. Sensor calibration is the process to adjust or fine-tune the sensor hardware to ensure accuracy and minimize the errors. Calibration involves comparing the expected output based on the theoretical models or standards with the actual measured output from the sensor. By precise adjustments, the sensor calibration enhances performance, accuracy, and reliability, which ensures that the sensor provides reliable data. On successful calibration and associated registry update (as described in the following sections), the value of ver registry item increments. For example, if the bias offset in registry item has ver value of 0, then on a successful calibration and registry update, the registry item is updated with the new bias offset and the ver value increments to 1. Note The <registry\_path> referred in the following sections should be considered as one of the existing paths on the device: /etc/sensors/registry/registry/ or /var/cache/sensors/registry/registry/. ## Factory sensor calibration The factory sensor calibration is a process to adjust or fine-tune the sensors during the manufacturing phase. ### Accelerometer The following table lists the accelerometer calibration procedure: Table : Accelerometer calibration | Command | Procedure | Bias values | | --- | --- | --- | | ssc_drva_test -sensor=accel -factory_test=2 -duration=10
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Note


A test result (PASS or FAIL) indicates only the test execution status whether the test is completed or not. | Run the command, while keeping the device stationary on a flat surface. | The following is the example of the QCS6490 device (ICM42688 sensor): The


`/qcs6490_rbx_icm4x6xx_0.json.icm4x6xx_0_platform.accel.fac_cal.bias`


file is created/updated automatically, and stores the bias offset after the calibration. | ### Magnetometer The following table lists the magnetometer calibration procedure: Table : Magnetometer calibration | Command | Procedure | Bias values | | --- | --- | --- | | NA | 1 Get /calculate corr_matrix and bias scale values (if applicable) for your device with the help of the sensor vendor.


2 Set the values into the corr\_matrix section in the platform-specific magnetometer JSON file of the sensor. | The following is an example of the QCS6490 device (AK09915 sensor):


The `/qcs6490_rbx_navmez_ak991x_0.json.ak0991x_0_platform.mag.fac_cal.corr_mat` file is created/updated automatically, and stores the bias offset after the calibration. | ### Proximity The following table lists the proximity calibration procedure: Table : Proximity calibration | Command | Procedure | Bias values | | --- | --- | --- | | ssc_drva_test -sensor=prox -factory_test=2 -duration=10
Copy to clipboard | 1 Keep an obstacle/object at a required distance (for example, 5cm or as mentioned in the specification) from the proximity sensor and run the command.


2 Verify that the test returns a PASS result.


3 This procedure uses 5cm as the threshold and the distance within the threshold is considered as near and the distance more than the threshold is considered as far. | The following is an example of the TMD3702 sensor:


The `/tmd3702_platform.prox.fac_cal`
file is created/updated automatically, and stores the bias offset after the calibration. | ### Ambient light The following table lists the ambient light calibration procedure: Table : Ambient light calibration | Command | Procedure | Bias values | | --- | --- | --- | | ssc_drva_test -sensor=als -factory_test=2 -duration=10
Copy to clipboard | Confirm the test procedure specified by the sensor vendor and run the command. | The following is an example of the TMD3702 sensor: The


`/tmd3702_platform.als.fac_cal`
file is created/updated automatically, and stores the bias offset after the calibration. | ## Runtime sensor calibration Runtime sensor calibration is a process to adjust or fine-tune the sensors during their operational phase, rather than during the manufacturing phase. It occurs dynamically while the sensor actively collects the data in the real-world scenarios. ### Gyroscope The gyroscope calibration sensor `gyro_cal` is used for gyroscope runtime calibration. The following table lists the gyroscope calibration procedure: Table : Gyroscope calibration | Command | Procedure | Bias values | | --- | --- | --- | | Use `see_workhorse` to enable a gyroscope calibration sensor (`gyro_cal`).


see_workhorse -sensor=gyro_cal -on_change=1 -duration=120 -display_events=1
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  • While keeping the device stationary, request the gyroscope calibration sensor gyro_cal data for more than 120sec and then stop.


  • After the command is executed, check the status field in the received event for the calibration accuracy status.




Note


The gyroscope sensor always produces noncalibrated values. Hence, for the client/algorithm that needs the calibrated gyroscope values run the `gyro_cal` sensor to generate and provide calibration offset/bias. The bias received from the `gyro_cal` sensor can then be subtracted as shown in the following pseudocode:


calibrated_gyro_x_val = (gyro_data.x_val - gyro_cal.x_bias);
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calibrated_gyro_y_val = (gyro_data.y_val - gyro_cal.y_bias);
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calibrated_gyro_z_val = (gyro_data.z_val - gyro_cal.z_bias);
Copy to clipboard | The `/sns_gyro_cal_persist_sX.bias` file (where, X = sensor index) is created/updated automatically, and stores the bias offset after the calibration:


Note


Gyroscope calibration runs approximately for every 60sec. The gyroscope bias is stored into the registry only after the existing streaming clients for the gyroscope are disabled. | ### Magnetometer The magnetometer calibration sensor `mag_cal` is used for the magnetometer runtime calibration. The following table lists the magnetometer calibration procedure: Table : Magnetometer calibration | Command | Procedure | Bias values | | --- | --- | --- | | Use `see_workhorse` to enable the magnetometer calibration sensor `mag_cal`.


see_workhorse -sensor=mag_cal -on_change=1 -duration=500 -display_events=1``
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  • Bring the device to an open area where there is no magnetic field interference.


  • Stream the magnetometer data and move the device in motion 8 for more than 60sec. Moving the device in motion 8 is mandatory.


  • After the command is executed, check the status field in the received event for the calibration accuracy status.


| The `/sns_mag_cal_persist_sXmY.bias` file (where, X = sensor index and Y = device mode index) is created/updated automatically, and stores the bias offset after the calibration. | Last Published: Dec 24, 2024 [Previous Topic Tools](https://docs.qualcomm.com/bundle/publicresource/80-70017-7/topics/test_tools.md) [Next Topic Verify](https://docs.qualcomm.com/bundle/publicresource/80-70017-7/topics/verify.md)