Hall effect sensors are miniature monolithic CMOS ICs (Integrated Circuits) which are designed to sense changing magnetic fields at close proximities and toggle its output accordingly. The theory was fundamentally discovered by the scientist Edwin Herbert Hall way back in the year 1879.
The main areas of applications of these devices mostly include speed measurements as in speedometers, frequency meters, tachometers etc.
A Hall effect sensor may primarily comprise of a temperature regulated Hall-plate along with a comparator stage, an active compensation network and an open drain output transistor.
To make the IC sense a magnetic field, it becomes important that the magnetic lines of flux strike perpendicular to its surface and is not beyond 5mm from the IC.
The above magnetic field is sensed by the Hall plate and a “Hall" voltage is developed across the biased Hall plate proportional to the induced magnetic flux. This voltage is compared with the internally set threshold of the IC in the comparator stage. If the applied magnetic flux is at optimal levels and exceeds the set threshold point, the open drain output transistor instantly switches, changes state and toggles the output.
The IC also incorporates an internal hysteresis control stage which monitors the threshold transitions and makes sure the output does not oscillate during the transition points.
Electronic devices usually may be quite prone to ambient temperature fluctuations which may drastically affect their output consistency. An internal temperature compensator inside Hall effect ICs is specially employed to tackle this problem. In case the ambient temperature tends to increase, the temperature-dependant bias stage raises the supply voltage of the Hall plate appropriately and compensates the falling induction of the magnetic field under the influence of high temperatures.
An internal active offset compensation system ensures constant magnetic response characteristics of the IC irrespective of voltage and temperature fluctuations.
All in all these ICs are reasonably robust by design and exhibit outstanding resistance against mechanical stresses.