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The unipolar Hall-effect switch is characterized by the magnetic operate threshold (Bop). If the Hall cell is exposed to a magnetic flux density greater than the operate threshold, the output transistor is switched on; by dropping below the threshold (Brp), the transistor is switched off. The hysteresis (Bhys) is the difference between the two thresholds (Bop-Brp). This built in hysteresis allows clean switching of the output even in the presence of external mechanical vibration and electrical noise. The digital output from a unipolar Hall-effect can be adapted to various logic systems. These devices are ideal for use with simple bar or rod magnets. Allegro offers a variety of unipolar Hall-effect switches that each have a different operate threshold and hysteresis with respect to the south pole of a magnet.

• Applications Note: Unipolar Hall-Effect Sensors