[1] A Hall effect sensor (HES) (or a Hall sensor/Hall probe) is any sensor based on the Hall effect (named after physicist Edwin Hall), in which a voltage is produced proportional to one axial component of the magnetic field vector B.
[1] Fig.1. a wheel with 2 magnets passing by a Hall effect sensor. The voltage from the sensor peaks twice per revolution. This arrangement is used to measure and regulate rotating objects' speed, like disk drives.
[3] A HES consists of a thing rectangular p-type semiconductor (like gallium arsenide GaAs, indium antimonide InSb or indium arsnide InAs) passing a continuous current throuhg itlsef. If the sensor is
[2] A Hall effect sensor, like the A3144, is a unipolar open-collector digital HES. Its pins are the VCC, for (4.5-24V) power input, ground, and output (which connects to ground). It works like a switch that activates based on a magnet's proximity.
It specifically works by connecting/shorting the output to ground when the magnet's south side approaches the sensor's front side - same response when the magnet's south side approaches its back side. Since the sensor can only pull the output down to ground, an external pull-up resistor connects to between the output and VCC pin.
[2] [3] A standard HES is normally off-state and turns on in a magnetic field's presence from a certain polarity or subjected to a magnetic field of enough strength.
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[2] The A3144 has a built-in Schmitt trigger, making it more stable by only switching on/off if magnetic field changes significantly, thus avoiding false triggers caused by small magnetic field changes or small fluctuations.
A common use of this is a tacometer where a magnet trigger points on a wheel to count rotation/speed.
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As current flows in a straight line while generating an electromagnetic fiel, in a HES, it flows through its VCC and GND pin.
Introducing an electromagnet device or magnet at the sensor, it interacts with the flowing current's electromagnetic field, deflecting (curve) its flow path, causing a charge imbalance across the circuit (one of the sensor's side has more charge than the other one.
This is the Hall effect and the force causing the electron deflection is the Lorentz force.
[3] The Hall effect specifically occurs by generating a measurable voltage via a magnetic field. For the a potential difference across the device to occur, the magnetic flux lines must be perpendicular, to the current flow and be of the correct polarity (often a south pole).
[2] The Hall effect provides info regarding on the magnetic pole type and the magnetic field size.
E.g., a south pole can cause the sensor to produce a voltage output while a north pole has no effect.
[4] Furthermore, by being in a magnetic field, the magnetic flux lines exert a force on the sensor's semiconductor material which deflects the charge carriers, electrons and holes, to either side of the semiconductor slab. This charge carrier movement is due to the magnetic force they experience passing through the semiconductor material.
A stronger magnetic fields causes more electron deflection in the HES and higher voltage deflection. Thus, HES can not only detect a magnetic presence, but also to what degree the magnetic force it detects is at.
[2] Unlike reed switches, which are electromagnetical devices activating in the presence of a magnet but can only open/close, HES have an analog measurement.
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[2] The HES below connects via wire leads to the 2 power terminals. The 2 orange pieces are soft iron flux concentrators that help increase the device sensitivity.
Note that iron's electricity and magnetism has an extremely high relative permeability rating, i.e., it causes flux lines to bunch together tightly.
[2] Placing a magnet is placed near the sensor makes the magnetic flux to concentrate and focus on flowing through the hull chip around in a continuous loop producing either a positive/negative voltage.
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[2] Placing the magnet on the other side makes the sensor to produce the opposite voltage polarity
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[2] The HES uses an internal amplifier to further increase the output signal's intensity.
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Analog and digital Hall sensors [2] In digital output sensors, after the amplifier the signal passes through a Schmitt trigger prior being output these use hysteresis to prevent contact bounce digital sensors are bistable devices that only either turn on/off.
[3] An analog HES' output signal is taken directly from the operational amplifier (output voltage proportional to the magnetic field through the sensor). The output Hall voltage is defined as:
VH = RH(I/t x B)
VH = Hall Voltage (in volts)
RH = Hall Effect coefficient
I = current flow through sensor (in amps)
t = sensor thickness (in mm)
B = magnetic flux density (in Teslas)
The formula calculates the voltage generated across a conductor placed in a magnetic field.
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Hall voltage formula derivation By applying a magnetic field, moving charges experience a magnetic force, the Lorentz force, which deflects them to one side, this charge separation creates a transverse electric field (EH). At equilibrium, the electric force (FE) balances the magnetic forces (FB).
qEB = qvdB
q = carrier charge (electron)
Canceling the charge (q) results in the Hall electric field: EH = vdB
vd = charge carrier's drift velocity
Relate electric field to the Hall voltage: The Hall voltage is defined as the electric field multiplied by the conductor width: VH = EHw
Substituting EH = vdB results in:
VH = vdBw
Relate the drift velocity to current: Know that electric current flowing through a conductor's cross-sectional area (A) is defined as: I = nqvdA
Since the cross-sectional area is the width multiplied area by the thickness (A = w*t):
I = nqvdwt
Solving for the drift velocity (vd):
vd = 1/(nqwt)
Substituting vd = 1/(nqwt) into VH = vdBw:
Bw1/(nqwt)
Solving this for VH: VH = (1/nq) (I/t x B) → VH = RH(I/t x B)
[2] Analog HESs use 2 preset values to show at what magnetic flux level the device will switch to high/low given these set thresholds A certain air gap distance can be determined for sensor activation linear or analog sensors have an output voltage that is directly proportional to the magnetic.
[2] Fig. 4
Gemini output:
[2] Fig. 4
[2] [3] A HES' output voltage, the Hall voltage (VH) is directly proportional to the magnetic field's strength (H) passing through the semiconductor material (VH ∝ H).
[3] This also allows the HES to work at wider ranges of power supplies and magnetic field conditions.
[2] IO having a digital output, the output can range from a 0 to a saturation point determined by the supplied voltage.
[2] Fig. 2. Digital (left) and digital output type (right)
HESs are mainly classified as either analog (linear), which output a continuous voltage proportional to magnetic field strength or digital, which output a binary high/low signal by crossing a magnetic threshold (Fig. 2).
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Note: In both rotational and head-on sensors, the magnet always faces directly at the sensor's head, to ensure max sensitivity. This is due to the flux must always be perpendicular where the magnet's pole is the highest.
[2] They can also be either unipolar or bipolar.
Unipolar HESs work like momentary switches, turning off in the presence of a magnetic (positive) south pole and turns off without the magnet. Such sensors are often unaffected by the (negative) north pole.
Bipolar HES work like latch switches, also turning on/off in a south pole's presence. It stays on it's removed, but turns off if a north pole approaches.
[2] Fig. 3
[2] HESs can also be either 2 detection configuration.
It can either detect a magnet moving in/out (back and forth) or a sideway detection with the magnet moving left/right in front of it.
Sideway detection are used in motors, where it can detect its number of rotation or speed by having the motor's each end to pass by each of the sensor.