One external magnetic source that is unavoidable in most operating settings is the Earth’s magnetic field, which ranges in magnitude from 22 µT to 67 µT at the Earth's surface depending on location and orientation. This error source can be quite important to consider, especially if the end equipment using the Hall-effect sensor is expected to capture precision measurements, and is traveling to multiple locations. Earth's Magnetic Field Diagram provides a simplified illustration of how the flux lines emanate out of the Earth. In reality, these flux lines will be slightly distorted. On a grand scale this may be due to variation in the material makeup of the Earth, while on a smaller scale this might be due to the materials of the building or structure in which the measurement device is housed.

As Earth's magnetic field is a vector quantity, the impact in design is influenced not only by the magnitude of the field, but also by the orientation of the device, which is important to consider if precision measurements are needed inside an end equipment that does not remain stationary.

As an example, Local Observations of Earth's Magnetic Field on TMCS1100A2, V_REF = 2.5 V provides measurements that were captured for x, y, and z axes respectively for a TMCS1100EVM locally in the magnetics lab in Tucson, AZ, to show the potential skew in output as the device orientation changes. Note that yaw rotation resulted in no change to the output, which is expected: the orientation of the device against the B vector does not change for this rotation.

As mentioned previously, however, this data is meant as an example only, and a similar test such as this may be required locally to quantify this impact for a given area, as the magnitude, as well as vector orientation, of the earth's field changes by location.