How does the magnetometer exactly work?

[Bartolomeo Rizzo]

Hello! 

I am a student and we used the app for a physics lab experiment. We measured Earth's magnetic field with the magnetometer.

With your group we were wondering how the magnetometer exactly works: does it only measure the absolute value of the magnetic field and then it derives the various components or, what we think is more likely, does it measure the three components and the absolute value is the vectorial sum of them?

Or maybe it measures all four of them?

We need to understand this for error propagation specifically.

Thankyou in advance!

[Jens Noriʇzsɔɥ]

The magnetometer measures the three components individually. For an analysis of uncertainties in your measurement, you should keep in mind a number of things
– first and foremost: unless you switched to “raw data” in the three dots menu, the data is calibrated in order to compensate for magnetic fields that are fixed to the smart device‘s orientation like internal currents,
– the calibration process typically involves data from the gyroscope (rotation rate sensor) and the accelerometer,
– the data is provided by the smartphone and/or sensor firmware, so we cannot definitely say that it is not averaged, for instance.

You could obtain accuracy information from the sensor‘s technical specification. On Android, you find the sensor identification by tapping the encircled “i” in the menu and “Device Info”. For Apple devices, you might find details on tear-down sites like iFixit or others. Then you need to search for details by the sensor manufacturer – if public. The sensors are driven in different modes, though, and you cannot be entirely sure which of these is used.