A Hall sensor integrated into a ferrite ring (as shown) can reduce the detection of stray fields by a factor of 100 or better (as the external magnetic fields cancel across the ring, giving no residual magnetic flux).
The ability for the Hall device to be shielded from stray magnetic forces (even the Earth's magnetic field can seriously impair an unshielded Hall device thus rendering it useless for accurate current measurement purposes) can be very effectively achieved by integrating the Hall device into a ferrite ring, an improvement of 100:1 is not unusual. This configuration also provides an improvement in signal to noise ratio and drift effects of over 20 times that of a 'bare' Hall device.
({{cc-by-sa-2.5}}—The ability for the Hall device to be shielded from stray magnetic forces (even the Earth's magentic field can seriously impair an unshielded Hall device thus rendering it useless for accurrate crrent measurement purposes) can be very e)