Overview
Many systems need to know where something is: a valve that opens to a set position, a stage that moves to a coordinate, a control knob that turns to an angle or a door that closes to a limit. A contactless position sensor measures it without a wear part, and the linear Hall-effect sensor from Allegro MicroSystems is a simple, robust way to do it. BeiLuo supplies these sensors with genuine traceability and FAE support.
The Linear Hall-Effect Principle
A linear Hall-effect sensor contains a Hall element that produces a small voltage proportional to the magnetic field passing through it. A target magnet moves with the object being measured, and the field at the sensor changes with the position, so the output voltage tracks the position. The Allegro A1324/5/6 family integrates the Hall element, the temperature compensation, a high-gain amplifier and a clamped output stage on one die, so the designer gets a clean analog signal with very little external circuitry.
Ratiometric Output
The output is ratiometric, which means it scales with the supply voltage, so a reading stays consistent even if the supply moves and it matches an ADC that shares the same reference. At zero field the output sits at half the supply, so a positive or negative field moves it above or below the midpoint, which makes a bidirectional measurement straightforward.
Choosing the Sensitivity
The sensitivity sets the output change per gauss, so it must match the field at the sensor. A high sensitivity such as 5.0 mV/G (the A1324) gives the largest output for a small field and a short air gap, while a lower sensitivity such as 2.5 mV/G (the A1326) keeps the output in range for a large field or a generous gap. Choosing the wrong sensitivity either wastes resolution or saturates the output.
Matching the Magnetic Circuit
The field at the sensor depends on the magnet, the air gap and the geometry, so the sensitivity is chosen together with the magnetic circuit. Model or measure the field across the travel range, then pick the sensitivity that keeps the output within its linear span at both ends while giving a good signal in the middle. Because the parts share a package, a prototype can be tuned by swapping the sensitivity.
The Magnetic Circuit and Air Gap
A consistent air gap is the key to a repeatable measurement. A mechanical stop or a bushing that fixes the gap keeps the reading stable, and a magnet with a stable temperature coefficient keeps the field stable over temperature. For a rotary measurement, two sensors placed in quadrature give the angle and the direction, and the field should vary smoothly and sinusoidally with the angle for the best accuracy.
Accuracy, Noise and Temperature
The device uses a proprietary dynamic offset cancellation technique to remove the offset drift and the low-frequency noise, which gives a low-noise output, a stable offset and precise recoverability after temperature cycling. The sensitivity is trimmed at the factory and is temperature-stable, and the device operates over -40 °C to +150 °C and is immune to mechanical stress for solid-state reliability.
Offset Cancellation
The chopper-stabilized front end removes the offset that would otherwise shift the reading, so a zero-field reading stays near half the supply over temperature. This is what makes the device suitable for a precise position measurement without a periodic recalibration.
Layout and Supply
Keep the supply clean and add the recommended bypass capacitor across the supply pins to realize the low-noise performance, keep the output trace short and away from switching nodes, and keep the sensor away from stray magnetic fields such as a nearby inductor or motor. Use the SIP package for a through-hole prototype and the SOT-23 package for a compact production board.
Getting Help
Send your travel or angle range, the magnet and the air gap, the supply and the accuracy target to our FAE team and we will propose a sensor and a sensitivity, help model the magnetic circuit and review the layout. BeiLuo holds mainstream Allegro magnetic sensors in regional warehouses and ships every order with an import declaration, a certificate of origin and a RoHS compliance file, so a position sensing design can move from prototype to production without a supply gap.